Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Forest Ecology and Management 158 (2002) 195±221 Physiological ecology of natural regeneration of harvested and disturbed forest stands: implications for forest management T.T. Kozlowski* Department of Environmental Science, Policy, and Management, University of California, Berkeley, CA 94720, USA Received 24 July 2000; accepted 26 November 2000 Abstract Forests are indispensable as sources of harvested products and a variety of services. Unfortunately forests throughout the world, and especially in the tropics, are threatened by natural and human-induced disturbances. Regeneration of harvested or otherwise severely disturbed forest stands typically occurs in four stages: (1) stand initiation and regeneration stage, (2) thinning or stem exclusion stage, (3) transition or understory regeneration stage, and (4) steady-state or old-growth stage. Blocks to stand regeneration may occur in each of these stages. Revegetation of severely-disturbed forests often is very slow and unpredictable because of complex interactions among propagules as well as site and climatic conditions. Stand regeneration depends on an abundant and viable seed supply, a suitable medium for seed germination, favorable environmental conditions, and capacity for sprouting or layering of some species. Massive losses of seeds in seed banks occur because of seed aging, failure of seed germination, predation, diseases, and death of seeds. Mortality of seedlings also is high, especially in the cotyledon stage of development, because of low reserves of carbohydrates and mineral nutrients. Growth of older seedlings, saplings, and mature trees is inhibited by air and soil pollution, drought, ¯ooding, soil compaction, insect attacks, and diseases. After canopy closure occurs in a developing forest stand changes in species composition are traceable to competition among plants for light, water, and mineral nutrients. Following severe disturbance of a multi-aged, mixed forest, a mixed-species stand of fast growing, generally short-lived trees typically occupies a site and is succeeded by species that dominated the stand before the disturbance occurred. After a minor disturbance gaps form in the canopy and are recolonized. If plant succession in a developing stand runs its full course the resulting old-growth forest is impacted by frequent minor disturbances and is maintained in an oscillating steady-state in which stand establishment, thinning, gap formation, and colonization recur. In some regions frequent ®res maintain forest stands in a subclimax stage of development. Natural regeneration of harvested or otherwise severely disturbed stands likely will be too slow and unpredictable to provide all the forest products and services required by increasing population growth. Hence, greater emphasis on several concurrent strategies will be needed, including heavy emphasis on arti®cial regeneration of disturbed forests; conservation of the remaining tropical forests; expansion of plantations, agroforestry systems, and forest reserves; expansion of tree improvement programs; more intensive and improved forest management; and expanded research with particular emphasis on seed biology, responses of tree species and genotypes to environmental stresses, tradeoffs between bene®cial and harmful effects of environmental stresses on tree species and genotypes, genetic engineering, potential effects of global warming on forests, agroforestry systems, models of stand productivity; and appraisal by remote sensing of injury to forest ecosystems. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Stand regeneration; Seed production; Seed germination; Competition; Succession; Management strategies * Present address: 2855 Carlsbad Blvd., S-326 Carlsbad, CA 92008, USA. 0378-1127/02/$ ± see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 8 - 1 1 2 7 ( 0 0 ) 0 0 7 1 2 - X 196 T.T. Kozlowski / Forest Ecology and Management 158 (2002) 195±221 1. Introduction Forests are enormously important to mankind. They not only supply essential harvestable products (e.g. wood, food, medicines, oils, gums, resins, and tannins), but also ornament landscapes; regulate climate, hydrology, mineral cycling, and soil erosion; create wildlife habitats; and purify the air and water (Gordon, 1996; Ferguson, 1996; Chapin et al., 1998; Kaufman et al., 1999). Unfortunately, the goods and services that forests can supply are threatened by a wide range of abiotic and biotic stresses. For example, disturbances of forests by excessive harvesting, insects, diseases, drought, ¯ooding, pollution, ®re, and soil compaction often result in catastrophic losses of both forest products and services (Kozlowski and Pallardy, 1997b; Kozlowski, 2000). There is particular world-wide concern about the high rate of loss of tropical forests, largely for wood, farming, and ranching (Ramakrishnan, 1995; Potter, 1999). Skole and Tucker (1993) estimated current deforestation in the Amazon Basin alone to be 380,000 km2 per year. About half of the destruction of tropical forests has been attributed to farming and one-fourth to cutting for lumber (Myers, 1996). Estimates of changes in the world's forested areas show a net loss of 56.3 million ha during 1990±1995. This value re¯ects a decrease of 65.1 million ha of forest in developing countries and an increase of 8.8 million ha in developed countries (FAO, 1997). In contrast to temperate forests most of the mineral pool in tropical forests is stored in the trees rather than in the soil (White, 1983; Jordan, 1985). Hence, ``slash and burn'' agriculture in the tropics inevitably leads to serious losses of nutrient capital. During repeated cultivation of cutover tropical forest lands nutrient pools are progressively depleted in harvested food plants and by leaching and volatilization. As a result, these previously-forested lands rapidly become unproductive, degraded, eroded, and waterlogged. Conversion of tropical forests to pastures also adversely affects the nutrient capital of these lands (Jordan, 1985; Medina, 1991). Several investigators have con®rmed that extensive deforestation in the tropics is followed by soil erosion, reduction in rainfall, lowering of the water-holding capacity of soil, increased ¯ooding, siltation of streams, and emission of CO2 to the atmosphere, with the latter effect contributing to potential global warming (Ramakrishnan, 1995; Houghton, 1995, 1998; Salati, 1997). Once a tropical forest is cleared of trees regeneration to primary forest may take many decades (Kozlowski, 1979). Temperate-zone forests are much more resilient than tropical forests to disturbance. When only some of the trees in a temperate forest are harvested, mineral losses typically are replaced by decomposing organic matter, weathering of soil minerals, N ®xation, and atmospheric deposits. Even clear-cutting of temperate forests on long rotations and with slash left behind may not seriously deplete the nutrient capital of a site (Kozlowski et al., 1991; Kozlowski and Pallardy, 1997a). Plantations of forest trees can appreciably compensate for losses of harvestable products from disturbed natural forests (Dekker-Robertson and Libby, 1998). Nevertheless, as the world's population grows, plantations alone are unlikely to satisfy human needs for all the bene®ts that forest ecosystems will be expected to supply. For example, there is concern about potential decreases in biomass production by second and subsequent rotations of plantations in Europe (Wormald, 1992), Australia (Keeves, 1996), and China (Ding and Chen, 1995; Sun Cuiling et al., 1997). Plantations often lead to reduced energy ¯ow through ecosystems, less nutrient cycling than in natural forests, and loss of mineral nutrients (Springett, 1976; Feller, 1978; Ewel et al., 1991). Short rotations of fast-growing trees in plantations often result in loss of soil fertility (Boyle, 1975; Evans, 1992). Plantations also provide conditions for spread of insect pests and diseases (Speight and Speechly, 1982; Zobel and Talbert, 1984; Zobel et al., 1987; Day and Leather, 1997; Dick, 1998). Moreover, most plantations lack the biodiversity needed for providing the raw materials that are essential for human activities (Pimental et al., 1992, 1997; Old®eld, 1995; Solbrig et al., 1996; Reaka-Kudla et al., 1997). Loss of biodiversity will lead to current or potential irreplaceable losses of foods, ®bers, and medicinal plants. Environmental stresses imposed on mixed-species forests may decrease biodiversity if they (1) alter genetic diversity within populations, (2) decrease reproductive potentials of species, (3) reduce crop yields or products of natural vegetation, or (4) adversely affect ecosystem structure and function (Barker and Tingey, 1992). There is a compelling need for establishing more forest reserves on productive sites in order to protect T.T. Kozlowski / Forest Ecology and Management 158 (2002) 195±221 wild genetic resources (Noss and Cooperrider, 1994; McNeely, 1994). Unfortunately many forest reserves have been and are being eliminated from unreserved lands. Furthermore, many existing reserves were established on unproductive sites characterized by low diversity and with relatively few important species of forest trees (Lindenmayer and Franklin, 1997). Hence, serious questions have been raised about reliance on existing forest reserves for conserving the important values of forest ecosystems (Franklin, 1993). Combinations of herbaceous and woody plants in agroforestry systems are important, especially in the tropics, for increasing yields of forest products, thus relieving pressure for harvesting of natural forests (Torres, 1983; Nair, 1989). Although approximately 2000 species of woody plants have shown some promise in agroforestry systems (Von Carlowitz, 1985) much needs to be learned about selection of appropriate species and genotype mixtures as well as management practices for agroforestry systems. Because of the foregoing considerations this review will emphasize that (1) natural regeneration of disturbed forest ecosystems is very slow and fraught with problems, and (2) impending increases in population growth will mandate a variety of concurrent managerial initiatives to supply the essential products and services that will be expected of forest ecosystems. 2. Stages of stand regeneration Natural revegetation of harvested or otherwise disturbed forest stands typically occurs in four sequential stages, including (1) a stand initiation and regeneration stage, (2) a thinning or stem exclusion stage, (3) a transition or understory regeneration stage, and (4) a steady-state or old-growth stage (Oliver, 1981; Oliver and Larson, 1996). Each of these stages exhibits some unique characteristics. Disturbances during any of these stages may induce physiological dysfunctions in trees and result in failure of adequate stand regeneration. 2.1. Stand initiation and regeneration stage Following tree harvesting or disturbances forest stands regenerate through interactions among propagules, including seeds in seed banks and those 197 dispersed into a site as well as sprouting or layering of residual trees, and soil and climatic conditions (Kozlowski, 1971). 2.1.1. Seed banks Regeneration of forest stands may occur from seeds stored in the soil, or in serotinous (late-to-open) cones in forest canopies. Some species (e.g. Pinus contorta, P. banksiana, P. rigida, P. clausa, P. attenuata, and Picea mariana) store viable seeds in cones that remain unopened while still attached to trees for many years. When the resinous material on serotinous cones is destroyed by forest ®res the cone scales open and the seeds are dispersed (Kozlowski et al., 1991; Kozlowski and Pallardy, 1997b). Both wind and animals play variable roles in establishing seed banks in disturbed forest stands. In temperate deciduous forests the seeds of Acer are dispersed by wind; those of Fagus by mammals or birds. In tropical forests dispersal of seeds of lianas depends more on wind than does dispersal of tree seeds. Dissemination of seeds by wind also occurs more commonly in dry tropical forests than in wet tropical forests (Leck, 1995). Most of the winddispersed seeds in forests are those of canopy trees or vines (Keay, 1957). Wind-dispersal distances vary greatly among seeds of different tree genera in accordance with the weights and structural modi®cations of seeds such as hairs (Salix, Populus, Platanus), wings (certain gymnosperms, Acer, Alnus, Betula, Dalbergia, Erythrina, Liquidambar, and Tilia). Whereas the heavy seeds of Pinus pinea are shed almost vertically, the small, large-winged seeds of Pinus radiata are disseminated for great distances (Wilgen and von Siegfried, 1986). The birds and mammals that carry seeds into disturbed forest stands improve germination capacity by partially digesting the seed coats. As the structural complexity of a forest stand increases, seed dispersal by birds becomes progressively important. Insects and bats also affect seed production by acting as pollinators (Darley-Hill and Johnson, 1981; Crawley, 1983; Leck et al., 1989; Leck, 1995; Waring and Running, 1998; Withgott, 1999). The full potential of seed banks for regenerating cutover and disturbed forest stands is never realized because of massive losses of seeds and young seedlings. Such losses have been attributed to seed aging, failure of 198 T.T. Kozlowski / Forest Ecology and Management 158 (2002) 195±221 seeds to germinate, predators, pathogens, seed redispersal, and seed and seedling mortality (Leck, 1995). After a heavy seed rain vast numbers of seedlings often emerge but most of them are desti-ned to die shortly. Forest trees face their greatest mortality risk in the ungerminated embryo stage of the seed or cotyledon stage of seedling development. Many seeds fail to germinate because of dormancy; others because of unfavorable environmental conditions. Mortality of seedlings in the cotyledon stage is particularly high because of their low reserves of carbohydrates and mineral nutrients. Hence, even mild environmental stresses often lead to seedling mortality (Kozlowski, 1976, 1979). Extremely high seedling mortality (up to 90%) during the ®rst year after emergence has been reported for Pseudotsuga menziesii (Gashwiler, 1967; Tappeiner and Helms, 1971), Eucalyptus spp. (Jacobs, 1955), Pinus thunbergii (Tazaki et al., 1980), and Acer saccharum (Hett and Loucks, 1971). 2.1.2. Seed production Greatest success in regeneration of forest stands almost always occurs after years of unusually heavy seed production (Smith, 1995). Accumulation of seeds in seed banks varies appreciably depending on the size of the seed crop and regularity of seed production by different species of plants. For example, Abies grandis and Pinus monticola produce relatively small seed crops, whereas Tsuga heterophylla produces large crops. Some species (e.g. Juglans nigra and Liriodendron tulipifera) have large seed crops at irregular intervals; others (e.g. A. saccharum and Fraxinus americana) at fairly regular intervals. In Alaska Betula papyrifera produces large seed crops once every 4 years on average; Picea glauca once every 10± 12 years (Perry, 1995). Some species (e.g. Magnolia grandi¯ora) produce good seed crops annually. To assist regeneration of cutover stands a few seed trees often are left behind. Seed trees are selected for high seed production by having large crowns, a high live-crown ratio (percent of length of stem with large branches) and strongly tapering stems (Kozlowski et al., 1991). 2.1.3. Seed longevity The life span of seeds of different species, which varies from a few days to years, in¯uences their potential for stand regeneration. Relatively short-lived seeds of temperate zone woody plants include those of Aesculus, Betuia, Carya, Populus, Quercus, Salix, Taxus, and Ulmus. Quercus acorns and Liquidambar seeds typically do not remain viable in the soil for more than 1 year, whereas Liriodendron seeds retain viability for up to 8 years (Little, 1974). Seeds of many tropical woody plants are very short-lived, including those of Cinchona, Cocos, Coffea, Erythroxylum, Hevea, Macadamia, and Thea (Kozlowski and Pallardy, 1997b). By comparison Albizia and Hovea seeds may remain viable for over 100 years (Osborne, 1980). It has been estimated that seeds of the chaparral plant, Ceanothus velutinus, may retain viability in forest litter for over 500 years. On sites where chaparral shrubs have died, because of shading or old age, C. velutinus stimulates the dormant seeds to germinate (Zavitkovski and Newton, 1968). During seed aging an initial decrease in germination capacity is followed by susceptibility to attacks by microorganisms, progressively shorter emerging radicles, and failure of cotyledon emergence as preludes to seed cling mortality. As seeds senesce their capacity for synthesizing proteins, lipids, RNA, enzymes, and repair systems declines, and injury to cell membranes and chromosomes increases (Harrington, 1972; Osborne, 1980; Roos, 1982; DeCastro and Martinez-Honduvilla, 1984; Priestley, 1986; Pukachka and Kuiper, 1988). 2.1.4. Seed germination The germination of seeds involves resumption of embryo growth and seed coat rupture, followed by seedling emergence. During germination the radicle typically elongates ®rst and enters the soil. The thin seed leaves (cotyledons) of most gymnosperms and angiosperms emerge above ground (epigeous germination). Exceptions are the ¯eshy cotyledons of some angiosperms (e.g. Quercus, Juglans, Hevea) which remain below ground (hypogeous germination). Epigeous cotyledons are important largely as photosynthetic organs and sometimes also for food storage. However, their storage function varies appreciably among species. Whereas the cotyledons of Acer negundo and Robinia pseudoacacia store large amounts of carbohydrates, those of Ailanthus altissima and Fraxinus pennsylvanica store only small amounts of carbohydrates but large amounts of lipids (Marshall and Kozlowski, 1976b). T.T. Kozlowski / Forest Ecology and Management 158 (2002) 195±221 Seed germination is characterized by cell division and expansion in the growing points of the embryo as well as intense physiological activity. An increase in seed hydration is accompanied by accelerated respiration (Vertucci and Leopold, 1987) and release of hormones that stimulate synthesis of enzymes involved in digestion of foods in storage tissues. Starches are hydrolyzed to sugars; fats to glycerol and fatty acids, with most of the latter converted to sugars by way of acetyl coenzyme A. Reserve proteins are broken down by proteolytic enzymes to soluble N compounds. The products of hydrolysis are then translocated to growing points where existing tissues expand and new tissues are produced. Simple carbohydrates are converted into cellulose; pectic compounds and lignin into new cell walls; amino acids and amides into the protein framework and enzymes of new protoplasm (Kozlowski and Pallardy, 1997a,b). 2.1.5. Seed dormancy Because seeds of most species of woody plants exhibit some degree of dormancy they may not germinate promptly under ostensibly favorable environmental conditions. Long postponement of seed germination often accounts for failure of adequate regeneration of forest stands. Seeds may be dormant for a variety of reasons, including (1) seed immaturity, (2) seed coat impermeability to water and/or oxygen, (3) seed coat resistance to embryo growth, (4) metabolic blocks in the embryo, and (5) various combinations of these. Sometimes viable seeds without primary dormancy lapse into a state of secondary dormancy when exposed to unfavorable environmental regimes (Mayer and PoljakoffMayber, 1989). Physiological maturity of seeds is associated with maximum germination capacity. Seeds usually are physiologically mature when resources from the mother plant have stopped moving into seeds. A variety of indicators have been used to judge maturity of seeds and fruits. These include color changes in fruits and cones (Schopmeyer, 1974), critical embryo size (Ching and Ching, 1962; Mercier and Langlois, 1992), amounts of stored seed sugars or fats (Rediske and Nicholson, 1965), and conductivity of seed leachates (Sahlen and Gjelsvik, 1993). Dormancy associated with impermeability of seed coats is common in many legumes (e.g. Robinia spp., 199 Gleditsia spp.) and some non-legumes (e.g. Tilia spp., Malus spp., and Pinus strohus). Examples of tropical species with impermeable seed coats include Podocarpus spp., Parkia javanica and Sindora coriacea (Sasaki, 1980a,b). Seed dormancy is most commonly physiological and involves failure of morphologically mature embryos to germinate. Embryo dormancy appears to be regulated by complex interactions of hormonal and other internal factors in the embryo and surrounding tissues. These interactions are in¯uenced by availability of light, water, and suitable temperature (Khan and Samimy, 1982; Battaglia, 1989). Physiological embryo dormancy often cannot be reversed by the same environmental conditions that induced it. In some species failure of seeds to germinate results from both restriction of a thick pericarp on expansion of the embryo and also on physiological embryo dormancy. Such double dormancy may occur in Ilex spp., Rosa spp., Taxus spp., Tilia spp., Cladrastis lutea, Pinus sabiniana, P. cembra, and P. albicaulis (Jackson and Blundell, 1963; Kozlowski and Pallardy, 1997b). In seeds of some species of Acer, including A. ginnala, A. negundo, A. pseudoplatanus, and A velutinurn, seed dormancy has been attributed to hard seed coats; in other species (A. platanoides, A. saccharum, and A. tataricum) to embryo dormancy (Pin®eld and Dungey, 1985; Pin®eld et al., 1987; Pin®eld and Stutchbury, 1990). Dormancy of Quercus nigra acorns was caused by mechanical strength of the pericarp, chemical inhibition of embryo growth by the pericarp, and slow imbibition of water (Peterson, 1983). 2.1.6. Seedling development During the earliest phases of seed germination cell division occurs throughout the embryo. Shortly thereafter cell division becomes localized in the apices of shoots and roots of young seedlings. A system of branches soon forms by development of leaves, nodes, and internodes from shoot apical growing points. Additional branches are produced later as a result of expansion of apical meristems in the lateral buds of bud clusters located at stem and branch apices, and also from elongation of adventitious and dormant buds distributed over the stem and branches. A taproot or primary root develops from the root apical meristem. The ®rst root either elongates and branches profusely 200 T.T. Kozlowski / Forest Ecology and Management 158 (2002) 195±221 or dies back. Many lateral roots arise from a deep pericycle layer (Kozlowski and Pallardy, 1997a,b). Reserve foods in the seed (which may include variable amounts of carbohydrates, fats, and proteins) sustain the growing embryo until epigeous cotyledons and/or foliage leaves develop suf®ciently to provide photosynthetic products to meristematic sites. Heavy seeds usually store large amounts of carbohydrates and sustain young seedlings better during environmental stresses than do small seeds (Buckley, 1982; Jones et al., 1994). 2.1.7. Vegetative propagation Revegetation of some species in cutover or disturbed stands occurs by sprouting from stumps or roots (Kozlowski and Pallardy, 1997a; Hoffmann et al., 2000). The sprouts that arise from root collars and lower parts of stems emanate from dormant buds that grow outward just under the bark. They typically develop into shoots only when growth of the tree crown is disturbed. Such sprouts account almost entirely for reproduction of some broad-leaved forests (e.g. Quercus spp.) in the eastern US (Braun, 1950). In Australia recruitment of seedlings after ®re was closely correlated with sprouting capacity (Benwell, 1998). Most chaparral species produce many stump sprouts. Not all do, however, and various species grow in combinations of intermixed sprouting and non-sprouting species (Biswell, 1974). Some species of broad-leaved trees regenerate largely by root sprouts (root suckers) that emanate from adventitious buds on roots. Such buds arise anew from cambial tissues. Both B. papyrifera and Populus tremuloides sprout abundantly after ®re and grow much faster than seed-producing conifers during the ®rst few years (Ahlgren, 1974; Dickmann and Stuart, 1983). Reproduction by root suckers also may occur in Fagus, Ailanthus, Liquidambar, Robinia, and Nyssa (Kozlowski et al., 1991). Although regeneration by sprouting is relatively unimportant in gymnosperms, a few species (e.g. Sequoia sempervirens, Pinus rigida, P. echinata, P. serotina, and Taxodium distichum) may sprout proli®cally, especially after ®re (Kozlowski et al., 1991). On some sites the capacity to form adventitious roots or reproduce by root suckers enables early successional species to tolerate the sedimentation that accompanies ¯ooding (Yarie et al., 1998). Some species regenerate by both sexual and vegetative reproduction. In the Mediterranean region many woody plants survive ®re by sprouting from dormant buds on the root crown and also from adventitious buds on lateral roots, stems, and old shoots. Regeneration also is supplemented by ®restimulated seed germination. Naveh (1974) classi®ed woody plants of Israel into (1) obligatory resprouters that depend entirely on vegetative propagation (e.g. Quercus coccifera, Q. calliprinos, and Pistacea lentiscus), (2) facultative resprouters that regenerate by both sprouting and seed germination (e.g. Calycotome villosa, Poterium spinosum, Erica arborea, Arbutus andrachne, and A. unedo). Some species are propagated by formation of roots on branches (layering). Although not very common, layering has been described for a number of genera of woody plants including Abies, Acer, Chamaecyparis, Cornus, Clethra, Picea, Taxus, and Viburnum (Lutz, 1939). Layering also is common in chaparral shrubs at high elevations where the weight of snow forces branches and stems down to the ground. Important shrubs that layer readily include Ceanothus cordulatus, Arctostaphylos patula, C. velutinus, and Quercus vaccinifolia (Biswell, 1974). In the Rocky Mountains dwarfed Picea engelmannii trees near the timber line reproduce by layering of their lower branches (Wardle, 1968). P. mariana and Thuja occidentalis in peat swamps may also reproduce by layering. 2.1.8. Environmental regulation of stand regeneration 2.1.8.1. Site characteristics. Wide differences among seedbeds in physical characteristics, supplies of water and mineral nutrients, and temperature often account for variations in regeneration of disturbed forest stands. When revegetation occurs from seeds the species that appear depend heavily on physical characteristics of the surface on which the seeds land. The most important determinants of success in reestablishment are the capacity of the surface medium to supply water and the amount of light that reaches the young seedlings. The denser the soil medium the better is its capacity to supply water to both seeds and germinants (Smith, 1995). Mineral soil generally is a good seedbed because of its high water in®ltration capacity, favorable aeration, and good hydraulic contact between soil particles and seeds (Winget and Kozlowski, 1965). Litter and duff T.T. Kozlowski / Forest Ecology and Management 158 (2002) 195±221 usually are less suitable because they do not warm rapidly and impede penetration of radicles, thereby preventing contact with mineral soil (Facelli and Pickett, 1991). Sphagnum moss and decayed wood usually are good seedbeds because of their high waterholding capacity (Place, 1955). Although P. menziesii seeds germinated readily on a variety of seedbeds if adequate moisture was available, only those seedlings with roots that rapidly contacted the mineral soil and were exposed to direct solar radiation survived (Weaver, 1974). Bumper seed crops of Pinus strobus in Minnesota forests every 3±5 years were followed by emergence of very many young seedlings. However, most of these seedlings died because their roots could not penetrate the thick dry humus to the wet mineral soil and because of their intolerance of heavy shade (Ahlgren, 1974). Mild compaction of soil may bene®t stand regeneration by improving capillary movement of water to seeds. Severe compaction, which is much more common, inhibits both seed germination and seedling growth, and also induces early seedling mortality. Compaction of soil is common in recreation areas such as picnic sites, timber harvesting sites, fruit orchards, agroforestry systems, and tree nurseries (Kozlowski, 1999, 2000). Compaction induces a variety of changes in soil structure and hydrology. It increases soil bulk density (mass per unit volume) (Purser and Cundy, 1992; Jim, 1993; Miller et al., 1996), decreases total pore volume (Currie, 1984) and the proportion of macropore space (Willatt and Pullar, 1983; Huang et al., 1996; Cassel, 1983; Malmer and Grip, 1990; Kramer and Boyer, 1995), increases water runoff (Kang and Lal, 1981; Nortcliff et al., 1990; Anderson and Spencer, 1991), and decreases soil aeration (Greacen and Sands, 1980; Wolkowski, 1990; Stepniewski et al., 1994; Horn et al., 1995). The many changes in soil structure and hydrology associated with compaction often lead to severe physiological dysfunctions in both seeds and seedlings. Water absorption usually is inhibited by plants and leaf water de®cits follow. The rate of photosynthesis is reduced by both stomatal and nonstomatal inhibition (Kozlowski, 1999). 2.1.8.2. Drought. The initial requirement for seed germination is imbibition of enough water to catalyze essential physiological processes in the embryo. Very 201 small amounts of water, usually only two to three times the weight of the seed, are necessary to soften seed coats and stimulate metabolic processes. After germination is completed, progressively greater amounts of water must be absorbed as the amount of foliage and transpirational water loss increase (Koller, 1972). Most viable seeds (except those with impermeable seed coats or impermeable layers under the seed coats) can imbibe enough water for germination from soil at ®eld capacity (Kaufmann, 1969). However, water absorption and germination capacity of seeds generally decrease rapidly as the soil dries below ®eld capacity (Satoo, 1966). Nevertheless, the tolerance of tree seeds to desiccation varies widely. Seeds of Quercus spp., Salix spp., Taxodium spp., and Ulmus spp. are more intolerant of desiccation than seeds of Pinus spp., Liquidambar spp., or Eucalyptus spp. (Kozlowski et al., 1991). The effect of drought on seed germination also varies with the temperature regime (Scifres and Brock, 1969). On most sites the majority of young tree seedlings die from desiccation during periodic droughts. 2.1.8.3. Flooding. Inundation of soil deprives seeds of the oxygen necessary for respiration. Hence, seed germination of many species is postponed or prevented by flooding (Kozlowski, 1985a; Kozlowski and Pallardy, 1997b). However, the germination capacity of flooded seeds varies appreciably among species and genotypes. Usually soaking of seeds of many upland species for hours to a few days stimulates germination; soaking for longer periods inhibits germination (Kozlowski, 1997). Seeds of some wetland species (e.g. Salix nigra) germinate readily under water (DeBell and Naylor, 1984). The seeds of Nyssa aquatica and T. distichum may retain viability when submerged for as much as 2 years. Seeds of these species typically germinate during dry periods when the soil surface is exposed (Smith and Linnartz, 1980). Once seedlings emerge their survival often depends on rapid growth and capacity to protrude above water level. In a ¯oodplain forest species with abundant food reserves in the large cotyledons (e.g. Q. nigra) had high survival rates, whereas seedlings of small-seeded species (e.g. Acer rubrum, Ulmus americana) and low cotyledonous food reserves showed low survival (Streng et al., 1989). 202 T.T. Kozlowski / Forest Ecology and Management 158 (2002) 195±221 2.1.8.4. Temperature. Both breaking of seed dormancy and subsequent germination are very responsive to temperature. In nature embryo dormancy in seeds of most temperate zone woody plants is broken by prolonged exposure to near-freezing temperature. Thereafter, much higher temperature regimes are required to stimulate the metabolic activity necessary for germination (Mayer and Poljakoff-Mayber, 1989). Dormancy of seeds with hard seed coats sometimes can be broken with high temperatures. For example, seed germination of some shrub species depends on fire to rupture the seed coat or melt seed coat waxes. Both heat and the action of fire scarified the seed coats of Ceanothus integerrimus, thereby increas-ing the capacity of the seeds to imbibe water (Biswell, 1974). A portion of the seed crop of some shrubland species (e.g. Adenostoma fasciculatum) germinated after a short period of ripening while the rest of the crop required heat to germinate (Christensen, 1995). Optimal temperatures for germination vary appreciably for seeds of different species. They are much higher for seeds of tropical species than those of temperate zone species (Bradbeer, 1988; Bewley, 1994). Seeds of many species will germinate over a wide temperature range (above a critical lower level). Examples are seeds of P. contorta (Critch®eld, 1957) and Picea engelmannil (Kaufmann and Eckard, 1977). However, there are exceptions and seeds of some species (e.g. Acer platanoides) germinate over only a narrow temperature range (Roe, 1941). 2.1.8.5. Solar radiation. Both seed germination and early seedling development are variously influenced by light intensity, light quality, and photoperiod. Seeds of most temperate-zone woody plants do not have a rigid light intensity requirement for germination, but a few do. For example, seeds of Betula and Pinus require very low illumination for germination. In forests dominated by Tsuga canadensis availability of light influenced seedling regeneration. Betula spp. seedlings were particularly sensitive, with low light reducing emergence by 43%, decreasing seedling growth by 99% and survival by 94%. Shading had less effect on performance of T. canadensis and P. strobus (Catovsky and Bazzaz, 2000). The seeds of many tropical species also require some light for germination (Hall and Swaine, 1980; Whitmore, 1983; Orozco-Segovia et al., 1993). Hence, seeds buried in soil or seeds in litter of these species may undergo enough shading to impede their germination. Seed germination of some species is also in¯uenced by photoperiod. Whereas earliest and greatest total germination of most light-sensitive seeds occurred in daily light periods of 8±12 h, germination of Eucalyptus sp. seeds was especially high in 8 h days and of Betula sp. seeds in 20 h days (Olson et al., 1959; Jones, 1961). Wavelength also has some effect on germination of seeds of several species including Betula pubescens, Pinus palustris, P. strobus, P. thunbergii, and P. virginiana. The effect of wavelength is regulated by the phytochrome pigment system, with germination stimulated by red light and inhibited by far-red light. Both metabolism and cell division in embryos are accelerated by red light and arrested by far-red light (Nyman, 1961; Taylorson and Hendricks, 1976; Hart, 1988). Seed germination sometimes is inhibited by the low red to far-red ratio of light transmitted by the litter layer on the forest ¯oor. However, stimulation of germination by red light varies considerably with prevailing temperature and seed hydration (Toole et al., 1961). The importance of light intensity for seedling growth is emphasized by the necessity of maintaining high rates of photosynthesis by seedlings very early in their development. Germination of pine seeds is typically followed by sequential development of cotyledons, primary needles, and secondary needles. Development of primary needles depends on cotyledon photosynthesis; development of secondary needles on photosynthate produced by the primary needles (Sasaki and Kozlowski, 1968a,b, 1970). When light intensity was low immediately after Pinus resinosa seeds germinated only few primary needles and no secondary needles emerged. When these shade-stressed seedlings were then exposed to higher light intensities the primary needles readily expanded and were followed by emergence and development of a normal complement of secondary needles. The importance of cotyledon photosynthesis for development of seedlings of broad-leaved trees was shown by suppression of seedling growth after the cotyledons of R. pseudoacacia were excised or cotyledon photosynthesis was inhibited by a chemical such as 3-[3,4-dichlorophenyl] 1-1, dimethylurea T.T. Kozlowski / Forest Ecology and Management 158 (2002) 195±221 (DCMU) (Marshall and Kozlowski, 1974, 1976a, 1977). 2.1.8.6. Pollutants and agricultural chemicals. Regeneration of forest stands often is adversely affected by a wide array of chemicals in the air and soil (Mudd and Kozlowski, 1975; Keller, 1983; Kozlowski, 1985b,c). Such compounds include some gaseous and particulate pollutants, herbicides, pesticides, growth retardants, and antitranspirants. Arrested stand regeneration may be associated with lowered seed production and inhibition of seed germination and plant growth, as well as accelerated plant mortality. These responses often follow injury to plants by chemicals as well as metabolic dysfunctions (Sasaki and Kozlowski, 1968c), with seedlings in the cotyledon stage of development especially vulnerable. Plant growth generally is arrested more by combinations of chemicals than by single chemicals (Kozlowski and Kuntz, 1963; Kozlowski and Torrie, 1965; Waisel et al., 1969; Kozlowski and Clausen, 1970; Wu and Kozlowski, 1972; Constantinidou and Kozlowski, 1979a,b; Suwannapinunt and Kozlowski, 1980; Norby and Kozlowski, 1981a,b,c; Olofinboba and Kozlowski, 1982; Shanklin and Kozlowski, 1984, 1985a,b; Kozlowski, 1985d, 1986c). The major environmental pollutants include sulphur dioxide (SO2), ozone (O3), ¯uorides, oxides of nitrogen (NOx), peroxyacetyl nitrates (PAN), and particulates (e.g. soot, cement-kiln dusts, lead particles, magnesium oxides, foundry dusts, and sulphuric acid aerosols (Mudd and Kozlowski, 1975; Kozlowski, 1980b, 1985c; Kozlowski and Constantinidou, 1986a,b). Pollutants sometimes reduce seed production and inhibit seed germination and plant growth (Constantinidou et al., 1976; Kozlowski, 1986b,c). The size of seed crops often is lowered after leaf injury by pollutants inhibits synthesis of carbohydrates and growth regulators. Pollutants may also alter mechanisms of ¯owering and fruiting and injure reproductive structures (Kozlowski et al., 1991; Kozlowski, 2000). Some pollutants lower the rate of photosynthesis by occluding stomatal pores, inducing stomatal closure, promoting disintegration of chlorophyll, and altering synthesis of photosynthetic enzymes (Mudd and Kozlowski, 1975; Norby and Kozlowski, 1982). In the long term total photosynthesis is lowered by a 203 reduction of leaf surface associated with leaf necrosis, abscission, and inhibition of leaf formation and expansion (Sasaki and Kozlowski, 1966; Barnes, 1972; Carlson, 1979; Lamoreaux and Chaney, 1978a,b; Heath, 1980; Eckert and Houston, 1980; Coyne and Bingham, 1982; Reich, 1983, 1987; Lorenc-Plucinska, 1978, 1982, 1988; Kozlowski and Constantinidou, 1986a,b; Oleksyn and Bialobok, 1986; Reich and Amundson, 1985; Tsukahara et al., 1985; Shanklin and Kozlowski, 1985a). Salinity inhibits seed germination not only by lowering the osmotic potential of the soil solution), thus inhibiting water absorption by seeds, but also by toxicity to the embryo (Khan and Ungar, 1984; Zekri, 1993). Whereas seed germination of nonhalophytes typically is arrested by 0.5% salt solutions, seeds of certain halophytes remain viable when exposed to vary strong salt solutions and germinate after the salt stress is relieved (Kozlowski, 1997). Considerable variation in effects of salinity on germination of seeds of different species of Casuarina was demonstrated by Clemens et al. (1983). Salinity may affect plant succession. Various species have different salt tolerances because salty soils vary in nutrieni balances, and toxic concentrations of different ions can develop, thus adversely in¯uencing the soil processes essential for uptake of N and P (Swanson et al., 1998). Some plants release toxic chemicals (allelochems) to the soil. These compounds may adversely affect seed germination and growth of neighboring plants (HytoÈnen, 1992). Allelocheins include phenolic acids, coumarins, quinones, terpenes, essential oils, alkaloids, and organic cyanides. These potentially toxic compounds are released by exudation, decay of plant tissues, leaching, and volatilization (Rice, 1974, 1984). Water-soluble toxic substances have been found in leaves, ¯owers, fruits, and/or roots of some chaparral species (e.g. Salvia arctostaphylos and Adenostoma fasciculatum). During ensuing rains the toxins are carried into the soil where they inhibit seed germination and growth of plants. After late-summer ®res destroy the toxins, regeneration of herbaceous plants and shrubs typically follows (Biswell, 1974). Although many laboratory experiments have phytotoxicity of allelochems their ecological signi®cance has been debated because accumulation of these compounds in forests is modi®ed by soil moisture as well 204 T.T. Kozlowski / Forest Ecology and Management 158 (2002) 195±221 as their destruction by soil micro¯ora (Kozlowski, 1995). Zackrisson and Nilsson (1992) and Nilsson (1994) demonstrated allelopathic effects of Empetrum hermaphroditum on regeneration of Pinus sylvestris stands in Sweden. Although appreciable amounts of allelochems were found in frozen soil, these compounds were detoxi®ed by microorganisms when ground ice was not present. A number of agricultural chemicals, including some insecticides, fungicides, herbicides, and antitranspirants are useful to indispensable in regenerating forest stands. However, regeneration sometimes is retarded by toxicity of high dosages or incorrectly applied chemicals. Sometimes these chemicals alter plant metabolism, arrest seed germination, and impede seedling growth as a prelude to early seedling mortality (Kozlowski and Kuntz, 1963; Kozlowski and Torrie, 1965; Sasaki and Kozlowski, 1968b; Waisel et al., 1969; Kozlowski and Clausen, 1970; Wu and Kozlowski, 1972; Olo®nboba and Kozlowski, 1982; Kozlowski, 1986a,c). Reduction in the rate of photosynthesis has been attributed to certain insecticides (Ayers and Barden, 1975), fungicides (Kozlowski and Keller, 1966, 1968; Keller, 1983), growth retardants (Roberts and Domir, 1983), and antitranspirants (Olo®nboba et al., 1974; Davies and Kozlowski, 1975). Symptoms of herbicide toxicity include inhibition of seed germination, chlorosis of seedlings, impeded seedling growth, and seedling mortality. Abnormal morphogenic changes such as fusion of cotyledons and swelling of stems often occur. Herbicide toxicity varies greatly with the stage of seedling development; herbicide dosage; method of herbicide application; and environmental conditions before, during and after herbicide application (Kozlowski and Kuntz, 1963; Winget et al., 1963; Kozlowski et al., 1967; Sasaki and Kozlowski, 1968b,c; Sasaki et al., 1968; Kozlowski and Sasaki, 1970; Wu et al., 1971; Wu and Kozlowski, 1972; Kozlowski, 1986a,b). Both ®lm-type and metabolic antitranspirants have been used to conserve water in plants and sometimes to reduce injury from insects, fungi, and salt spray (Kozlowski, 1986b). In some cases ®lm-type antitranspirants (e.g. oil, silicones, plastics, latex and resins) were bene®cial in reducing water loss and increasing plant growth (Davenport et al., 1972; Chalmers et al., 1983). However, some ®lms caused chlorosis, leaf lesions, leaf abscission, and plant mortality. Certain antitranspirants variously lowered the rate of photosynthesis when they accumulated in antestomatal chambers and prevented diffusion of atmospheric CO2 to the leaf mesophyll cells (Davies et al., 1974; Lee and Kozlowski, 1974; Davies and Kozlowski, 1975). Solarova et al. (1981) concluded that ®lm-type antitranspirants reduced transplanting shock in trees but were a problem because they were less permeable to CO2 than to water vapor. Several metabolic antitranspirants (e.g. abscisic acid, succinic acids, phenylmercuric acetate, and atrazine) reduced transpirational water loss by promoting stomatal closure (Davies and Kozlowski, 1975) but some were phytotoxic. For example, decenylsuccinic acid not only injured P. resinosa needles and inhibited bud development but also induced early mortality of seedlings (Kozlowski and Clausen, 1970). Phenylmercuric acetate closed stomata of B. papyrifera leaves but also caused chlorophyll breakdown (Waisel et al., 1969). Furthermore, there is the added danger of releasing mercury compounds into the atmosphere. 2.2. Thinning or stem exclusion stage The most prevalent feature of this stage, beginning with canopy closure, is accelerated mortality of trees and changes in the dominant trees of monocultures or variations in species in mixed-species stands. These changes often have been attributed to competition among plants for solar radiation, water and mineral nutrients. In Costa Rica the poor growth of Cedrela odorata in mixture resulted from early onset of severe competition with Cordia alliodora and Hyeronima alchorneoides (Manalled et al., 1998). 2.2.1. Competition for resources In forest stands the light intensity typically decreases progressively from above the canopy to the forest ¯oor. For example, less than 5% of the light intensity was transmitted to the forest ¯oor in a 150year-old Fagus grandifolia stand (Trapp, 1938). In a 50-year-old L. tulipifera forest most light reached the forest ¯oor in the spring before the leaves begun to expand; the least light during short autumn days while the trees still retained all their leaves (Hutchinson and Matt, 1977). The light intensity that penetrates a forest canopy may be only 10±15% in open, even-aged Pinus T.T. Kozlowski / Forest Ecology and Management 158 (2002) 195±221 stands and less than 1% in some tropical rain forests (Spurr and Barnes, 1980). Understory plants of dense forest stands are exposed to prolonged dim and diffuse irradiance punctuated by short periods of sun¯ecks. The duration of sun¯ecks may vary from seconds to under 2 min in tropical forests to ``sunpatches'' of 1 h or more in open coniferous forests. Sun¯ecks sometimes comprise up to 80% of the total irradiance at the forest ¯oor (Chazdon and Pearcy, 1991). Physiological responses, growth, and survival of many understory plants are appreciably in¯uenced by sun¯ecks (Pearcy, 1983). Examples include Euphorbia forbesii and Claoxylon sp. (Oberbauer et al., 1988). Growth increases due to sun¯ecks may be counteracted by de®cits of water or mineral nutrients, as well as high leaf temperatures (Pearcy et al., 1994). Increased growth of understory plants exposed to sun¯ecks is associated with stimulation of photosynthesis as shown for Fraxinus excelsior, Fagus sylvatica, and Ilex aquifolium (Harbinson and Woodward, 1984) and several rain forest species (Pearcy et al., 1985; Chazdon and Pearcy, 1986). The photosynthetic responses to sun¯ecks are affected by light conditions experienced by plants before a sudden increase in irradiance as well as by the extent of the increase in irradiance. Hence, sun¯ecks exert a carryover stimulation of photosynthesis after it is induced by light (Pearcy et al., 1985). For three understory species (Fagus crenata, Acer ru®nerve, Daphniphyllum humile) in a F. crenata forest in Japan the period of photosynthetic induction was several times longer when irradiance was increased from darkness to 800 mmol m2 s 1 than when irradiance was increased from darkness to 1500 mmol m 2 s 1 (Han et al., 1999). Fluttering of upper canopy leaves of P. tremuloides was followed by an increase in the number of sun¯ecks and in enhanced photosynthesis in the lower canopy (Roden and Pearcy, 1993). The importance of competition for water was emphasized by greater availability of water and higher growth rates of the residual trees following thinning of P. resinosa and P. menziesii stands (Sucoff and Hong, 1974; Aussenac and Granier, 1988). Leaf hydration of P. contorta trees was higher in thinned than in unthinned stands (Donner and Running, 1986). Competition for soil water also was shown between 205 Abies concolor saplings and chaparral shrubs (Conard and Radosevich, 1982), between P. menziesii trees and Ceanothus velutinus shrubs (Petersen et al., 1988), and between Pinus ponderosa seedlings and several species of grasses (Elliott and White, 1987). Competition for mineral nutrients among individual woody plants as well as among woody and herbaceous plants is well documented (Bell, 1968; Atkinson and Johnson, 1979; Haynes and Goh, 1980; Connor, 1983; Van den Driessche, 1984). Both N and P concentrations were lower in closely spaced Pseudotsuga menziesii trees than in widely spaced trees (Cole and Newton, 1986). In F. sylvatica forests both trees and shrubs competed with herbaceous plants for Fe, N, K, and P (Olsen, 1961). As plant competition intensi®es some trees express dominance and grow rapidly while others grow slowly and occupy low canopy positions. The competitive capacity of the more suppressed trees declines progressively and their growth rates decrease accordingly. Between the stem initiation stage and thinning stage growth ef®ciency (stem wood production per unit of leaf area) decreases greatly, sometimes by more than 90% (Waring and Running, 1998). Eventually the most suppressed trees die. The leaf area index of a regenerating forest stand becomes maximal during the thinning stage. Net addition of foliage to the canopy stabilizes and there is a transfer of leaf area from suppressed trees to more dominant ones (Waring and Running, 1998). Competition is especially intense within monocultures (intraspeci®c competition) where resource requirements are more or less similar for all trees. In mixed-species stands the differences among species in depths of rooting and in patterns of absorption of mineral nutrients may account appreciably for variations in availability of resources (Schulze et al., 1994). Because forest stands generally are quite variable the impacts of competition on plant community structure may be in¯uenced to considerable degree by a variety of environmental factors. As emphasized by Perry (1995) (1) species may not need to compete when their growth is largely in¯uenced by predation, disturbance, or climatic perturbation (e.g. when herbivores and pathogens increase biodiversity by lowering the capacity of one species to dominate others), (2) competing species may actually bene®t 206 T.T. Kozlowski / Forest Ecology and Management 158 (2002) 195±221 each other by either decreasing or eliminating the adverse effects of plant competition (e.g. by improving the soil or microclimate, reducing the in¯uence of other competing plants, discouraging predators, catalyzing bene®cial components in the root zone, and attracting pollinators) (Hunter and Aarssen, 1988) (3) trees may avoid competition through specialization. For example, early-colonizing N-®xing plants compete for resources, but later bene®t each other by increasing soil fertility. Much rigid emphasis on the importance of plant competition alone in structuring ecosystems evolved from mathematical models that portrayed interacting plant species as if they lived in a constant environment and were isolated from other species in the system (Perry, 1995). Stone and Roberts (1991) concluded that up to 40% of the interactions among species were advantageous when removed from the community context in which they occurred. Only in a nearly constant environment are species adversely affected by other species. Hence, species often depend on each other in ways that are not always obvious, thus greatly modifying the adverse effects of plant competition. 2.3. Transition or understory regeneration stage Dominant features of this stage are death of some overstory trees, resulting in formation of gaps in the canopy and reintroduction of understory vegetation. Formation of canopy gaps allows more solar radiation to reach the forest ¯oor and enhance growth of trees that were suppressed in the previous (thinning) stage. Gap sizes vary appreciably. Small gaps form often because of death or windthrow of a few trees; the less frequent large gaps are traceable to various disturbances, including ®res, hurricanes, and insect attacks. In temperate forests very small gaps are ®lled by extension of branches of surrounding trees; larger gaps close by growth of saplings and sprouts within a gap. Large gaps very often are colonized by early shadeintolerant species and later replaced by shade-tolerant species. Or species of both groups may colonize a gap more or less concurrently, with the faster-growing, short-lived pioneer species eliminated after a period of dominance (Runkle, 1985). In tropical forests the majority of gaps are small even though most of the total gap area is in a few large gaps. Very small gaps typically are ®lled by growth of branches of adjacent trees; somewhat larger gaps by growth of seedlings that were suppressed prior to canopy opening, and by sprouting; still larger gaps by plants from seeds in soil banks. The largest gaps are ®lled mostly by plants produced from seeds brought in primarily by animals and wind after the gaps formed (Bazzaz, 1984; Swaine and Whitmore, 1988; Whitmore, 1989). Well-constructed models are potentially useful for studying species dynamics and predicting effects of combinations of factors that may in¯uence growth and development of disturbed forest ecosystems (Kaufmann and Linder, 1996; Landsberg and Gower, 1997). Botkin et al. (1972) pioneered in appraising tree mortality and regeneration of gaps in forests by a model that simulated vegetation dynamics. Many modi®ed gap models were subsequently introduced to evaluate such aspects of stand growth dynamics as recruitment of propagules, seed germination, and tree mortality (e.g. Cattelino et al., 1979; Dale et al., 1985; Bonan, 1989; Bossel, 1991; Huston, 1991; Solomon and Bartlein, 1992; Shugart et al., 1992; Friend et al., 1993; Pacala et al., 1993, 1996; Korol et al., 1995, 1996; Roberts, 1996a,b; Keane et al., 1996). Gap models usually incorporate such site variables as species lists and maximum tree sizes, diameter and height growth of trees, entry of young trees into the simulation, mortality data, and growth-limiting potentials of available resources (Waring and Running, 1998). 2.4. Steady-state or old-growth stage Salient characteristics of this stage are continuation of a series of successional stages that began in the previous stage that may culminate in an old-growth climax forest. 2.4.1. Succession Disturbed plant communities tend to regenerate to a previous condition if they are not exposed to additional stresses. Whereas competition among trees in a monoculture does not involve succession, competition in a mixed-species forest stand progresses toward a more-or-less stable climax community with high capacity for tolerating the stresses of competition. However, an old-growth community often is not T.T. Kozlowski / Forest Ecology and Management 158 (2002) 195±221 achieved because of the long time required for succession to run its full course and the strong likelihood of interruption by recurrent disturbances (Kozlowski, 1995; Perry, 1995). Examples of forest succession to old-growth forest are replacements of early-colonizing stands of Pinus taeda and P. echinata of the southeastern US by Quetcus-Carya stands as the overstory Pinus species die when they become overmature in 70±80 years. In the northeastern US fast-growing shade-intolerant Prunus pensylvanica trees dominate forest stands in early succession and are replaced by slower-growing more shade tolerant species. Following early land clearance for agriculture in Massachusetts the abundance of long-lived shade tolerant species (T. canadensis, F. grandifolia, and Betula alleghaniensis) declined sharply. These were replaced by species more tolerant of disturbance (P. strobus, Castanea dentata) which in turn were succeeded by Quercus spp., A. rubrum, and Betula sp. (Fuller et al., 1998). Composition of the early colonists during succession depends on the severity of disturbance of forest stands. Early successional species usually are better represented than late successional species in seed banks (Leck, 1995). Hence, after severe stand disturbance the early-colonizing, fast-growing, usually short-lived species dominate a site and later are replaced by species that were the dominants prior to disturbance. The replacement species may arise from seeds, sprouts, or residual plants that survived the disturbance. After minor disturbances gaps form and are recolonized. In addition to the effect of severity of disturbance the composition of the early-successional species is in¯uenced by the time of year and length of time between disturbances (Perry, 1995). In Alaska most ®res occur in June and July, when ripe seeds of P. tremuloides and P. balsamifera are shed, well before those of B. papyrifera and P. glauca. On a wide variety of sites ®re in midsummer is less likely to be followed by regeneration through abundant sprouting than ®re occurring during the dormant season. Production of stump sprouts and root suckers depends on the level of stored carbohydrates in plants, which typically is much higher in the dormant season than in midsummer when trees have depleted most of their carbohydrate reserves during shoot elongation and leaf expansion (Clark and Liming, 1953; Bachelard and Sands, 1968; Kozlowski, 1992). Sprouting of 207 Miconia albicans and Clidemia sericea after ®re was highly correlated with the amount of root starch (Miyanishi and Kelman, 1986). The sprouting capacity of Eucalyptus viminalis depended on the amount of starch in the sapwood (Bamber and Humphreys, 1965). Abundance of root suckers of P. tremuloides also depended on stored carbohydrates (Schier and Zasada, 1973). The species composition of a pioneer forest community often varies with the time between disturbances. For example, when ®res occur frequently P. contorta precedes establishment of T. heterophylla. However, T. heterophylla may succeed itself if the interval between ®res is so long that P. contorta has already died out (Perry, 1995). Succession in disturbed tropical forests to reestablishment of primary forest is very slow. Following clear-cutting of primary forest a dense growth of weeds, shrubs, vines, and young trees typically emerges. Fast-growing, very-short-lived trees then become dominant and are succeeded by slowergrowing, longer-lived species. Succession progresses slowly until the climax species are reestablished, sometimes only after hundreds of years. If the course of succession is interrupted by additional disturbances, more mineral nutrients are lost from the soil, thus rendering the site unsuitable ®r even the early successional tree species (Kozlowski, 1979; Kozlowski et al., 1991). Many early studies in the tropics gave little attention to the importance of secondary forests (woody revegetation after removal of much or all of a primary forest) in biomass production and carbon ¯ux. It has now been well documented that secondary forests play an important though variable role in carbon sequestration in tropical forest ecosystems. The rate of biomass production differs appreciably with the forest type, age of the secondary forest, history of use of cleared areas, number of times an area has been cleared, and soil fertility (Uhl et al., 1988; Moran et al., 1994; Fearnside, 1996; Nelson et al., 2000). Carbon accumulation rates in tropical moist, seasonal, and open forests (which varied from rain forest types to dry wooded savannas) were about 5, 4, and 3 t ha 1 per year, respectively (Houghton et al., 1991). Accumulation of biomass in a disturbed Belgian Congo forest varied from 19 t ha 1 per year for the ®rst 8 years to only 2.5 t ha 1 per year during 208 T.T. Kozlowski / Forest Ecology and Management 158 (2002) 195±221 the next 9 years (Lugo and Brown, 1982). In Para, Brazil abandoned pastures that had been lightly grazed accumulated biomass at approximately 10 t ha 1 per year whereas pastures that had been moderately grazed produced biomass at about half that rate (Uhl et al., 1988). 2.4.2. Mechanisms of succession Successional trajectories are in¯uenced by two primary factors: (1) the species that comprise the initial colonists on a disturbed site, and (2) the impacts of the initial and succeeding dominants on subsequent conditions and events (Perry, 1995). Regulation of growth and survival of seral plants during succession is complex. It typically includes aspects of facilitation and inhibition and is affected by interactions among resource availability, climate, animals, pathogens, mycorrhizal fungi, and other microbes. Furthermore, the nature of the interactions changes over time (Connell and Slatyer, 1977; Perry, 1995). According to the facilitation model the early successional species modify the site and render it more suitable for establishment and growth of later successional plants. Site modi®cation is accomplished by weathering of rocks, accumulation of mineral nutrients and carbon, and provision of energy that allows plants to build soil and absorb mineral nutrients. An example of facilitation is the ``island effect'' characterized by establishment and growth of plants near nurse trees or shrubs. Nurse trees may shelter seedlings from environmental extremes, act as centers for seed dispersal (e.g. by birds), and provide local sites with enriched soil. Plant islands also may facilitate establishment of late-arriving species by in¯uencing soil chemistry, biology, and structure. Early colonizers also may facilitate colonization of succeeding species by providing a legacy of mycorrhizal fungi (Perry, 1995). The inhibition model is based on changes in availability of resources during plant succession (Tilman, 1985). Once the early colonizing plants obtain space and available resources, they either arrest invasion by subsequent colonists or suppress those present. Sometimes early colonists comprise a dense monoculture that slows or precludes invasion by other species. For example, in South America trees do not readily invade abandoned pastures because of inadequate seed dispersal to grasslands; consumption of tree seeds and seedlings by rodents; competition between grasses and trees for solar radiation, water, and mineral nutrients; and mortality of tree seedlings by recurrent burning of grasslands (Nepstad et al., 1990). 2.4.3. Characteristics of old growth forests Should the course of succession be completed, the resulting old-growth forest has become multi-aged in contrast to the even-aged character of earlier successional communities. The dominant trees of old-growth forests show little height growth, whereas diameter growth continues. As a result live biomass reaches a maximum and stabilizes in the old-growth stage. Species composition, community height, and structural diversity also maximize in the old-growth stage, even though the number of plant and animal species together may be higher in the stand initiation stage (Oliver and Larson, 1996). In general growth ef®ciency of all the trees in an old-growth forest tends to be lower than it was in earlier successional slages. Old-growth forests are impacted by frequent minor disturbances (including death of some old trees, windthrows, or ground ®res) and often less-frequent harsh disturbances such as severe crown ®res. Hence, they are not completely stable, but are maintained in an oscillating steady-state and consist of mosaics of patches of various sizes and ages. In such forests the processes of establishment, thinning, gap formation, and recolonization recur. When old-growth forests are impacted by the infrequent major disturbances they are maintained in a steady-state only within large landscapes (Perry, 1995). In many regions succession to an old-growth forest is arrested by frequent severe ®res. For example, in the southeastern US subclimax P. taeda, and P. echinata forests are maintained by ®re (Komarek, 1974). In the western US P. menziesii is a major ``®re-climax'' species (Kozlowski et al., 1991). In the northeastern US P. tremuloides, Pinus banksiana, and P. mariana are maintained on many sites by ®re. Adaptations of ®re-tolerant species include stimulation by ®re of seed dispersal, seed germination, and ¯owering, as well as seed storage in the soil or on plants (in serotinous cones), thick bark, and capacity for sprouting (Gill, 1981; Gill and Groves, 1981; Hanes, 1988; Biswell, 1989; Kozlowski et al., 1991; Kozlowski and Pallardy, 1997a,b). T.T. Kozlowski / Forest Ecology and Management 158 (2002) 195±221 3. Conclusions Accelerating rates of destruction of forest ecosystems, especially in the tropics, often result in catastrophic losses of the harvestable forest products and a variety of services essential for maintaining Earth's life support systems. Natural regeneration of disturbed mature forests to a predisturbance condition often is slow, unpredictable, and fraught with dif®culties. Because of the added demands made on forests by a rapidly growing human population, reliance on natural regeneration is questionable. Hence, much emphasis is needed on abetting natural regeneration with arti®cial methods, including direct seeding with high-quality seed, outplanting of superior planting stock, and intensive site preparation (Smith, 1995). However, ef®cient regeneration of disturbed forest stands can provide only a partial solution to meeting the nearfuture demands for more forest products and services inevitably associated with a burgeoning population growth. To not only regenerate and accelerate growth of disturbed forests but also to maintain their sustainability and biodiversity several concurrent initiatives are needed including: (1) preservation of the remaining tropical forests for their wild genetic resources. Especially needed is better understanding of ways in which biodiversity and ecosystem functioning are coupled (Dasgupta et al., 2000). Evolution of strategies for achieving sustainability of tropical forests will require cooperation among forest biologists, social scientists, and economists; (2) expansion of plantations (Zobel and Talbert, 1984; Evans, 1992; DekkerRobertson and Libby, 1998); (3) establishment of large forest reserves on carefully selected sites for preservation of wild genetic resources (Noss and Cooperrider, 1994; McNeely, 1994); (4) expansion and international support of agroforestry system (Vergara and Nair, 1983; Nair, 1998); (5) improved forest management (e.g. timing of tree harvesting to coincide with good seed years; long rotations; decreasing human-induced environmental stresses such as pollution, drought, ¯ooding, ®re, and soil compaction which are avoidable to various degrees) (Kozlowski, 2000); more intensive management of plantations, forest reserves, and agroforestry systems (e.g. greater emphasis on irrigation, fertilizer application, site selection, and site preparation) (Kozlowski et al., 1991; Kozlowski and Pallardy, 1997b); (6) expansion of tree improvement 209 programs (e.g. selection of trees in small populations to maximize the rate of improvement in one or a few characters; mating of selected parents in different combinations; selection of superior genotypes followed by propagation in seed orchards for testing, breeding, and seed production) (Guries, 1995); (7) expansion of research with focus on both regeneration and preservation of forest ecosystems as well as accelerated productivity (Landsberg and Gower, 1997; Kozlowski, 2000). We do not know enough about many disturbed forest ecosystems to regenerate them rapidly and ef®ciently. Hence, much more research is needed on how to maximize yields of forest products and services while maintaining sustainability and biodiversity of forest stands. Determinations of how physiological dysfunctions are induced in trees by environmental stresses will require a long-term commitment to ecological research (Likens, 1983, 1985, 1987; Franklin, 1987; Lindenmayer and Franklin, 1997). Some examples of priority research areas include the following: 1. Seed biology: this includes indices of seed maturity, control of seed quality, variations in dormancy of seeds of various species and genotypes, causes of seed aging, effects of environmental stresses on seed development, and factors in¯uencing seed vigor. 2. Seedling biology: this includes physiological determinants of growth of seedlings (especially in the cotyledon stage of development), effects of environmental stresses on seedling vigor, and causes of mortality of seedlings beyond the cotyledon stage of development. 3. Responses of various species and genotypes to disturbances: this includes controlled environment research on impacts of environmental changes, stresses, and their interactions on physiological processes, growth, and survival of woody plants, and effects of environmental preconditioning in plant responses to disturbances (Norby and Kozlowski, 1981a,b,c; Kozlowski and Huxley, 1983; Shanklin and Kozlowski, 1985a,b). 4. Tradeoffs between bene®cial and harmful effects of environmental extremes on various species and genotypes: not all environmental stresses are harmful to plant ecosystems. In the past much preoccupation with the deleterious impacts of 210 T.T. Kozlowski / Forest Ecology and Management 158 (2002) 195±221 environmental extremes obscured some of their potentially bene®cial effects which sometimes might be incorporated in forest management plans. Examples include some effects of drought, ¯ooding, and ®re. Wherever woody plants grow their development and survival depend on adequate water supplies. Water de®cits adversely affect several physiological processes, resulting in loss of vegetative and reproductive growth, as well as in injury and mortality of plants (Kozlowski, 1968, 1972, 1979, 1982a, 1983, 1996). Nevertheless, slowly increasing droughts often induce physiological adjustments in woody plants that protect them from the adverse responses that inevitably occur following abrupt imposition of drought. Hence, seedlings preconditioned by exposure to mild water stress in forest nurseries undergo less growth inhibition and injury from transplanting and drought than seedlings not previously drought-stressed (Clemens and Jones, 1978; Abrams, 1988; Mexal and South, 1991; Kozlowski and Pallardy, 1997b). Exposing fruit trees to water stress during a critical early period of fruit development to inhibit vegetative growth, followed by normal irrigation, favored formation of ¯ower buds and increased fruit yield (hence larger seed crops) in several species (Menzel, 1983; Southwick and Davenport, 1986; Menzel and Simpson, 1990). A period of drought also stimulated breaking of dormancy of ¯ower buds (Barbera et al., 1985; Shalhevet and Levy, 1990) and increased fruit yields (Chalmers et al., 1983, 1984; Mitchell et al., 1984, 1986). The deleterious effects of ¯ooding on woody plants have been well documented. They include physiological dysfunctions, inhibition of seed germination and growth of plants, as well as plant injury and mortality (Kozlowski, 1982b, 1984a,b,c; Newsome et al., 1982; Tang and Kozlowski, 1982a,b, 1983; Kozlowski and Pallardy, 1984; Tsukuhara and Kozlowski, 1986; Reid and Bradford, 1984; Sena Gomes and Kozlowski, 1986, 1988; Yamamoto and Kozlowski, 1987a,b; Kozlowski and Pallardy, 1997b; Lopez and Kursar, 1999). However, ¯ooding sometimes has bene®cial effects that can be judiciously used in forest management plans. For example, ¯ooding for short periods during the dormant season may stimulate subsequent vegetative growth or favor reproductive growth over vegetative growth. ``Greentree reservoirs'', shallow impoundments during the autumn and winter, sometimes have been advantageously created to inhibit vegetative growth and thereby stimulate reproductive growth of woody plants in order to provide food (mast) for wildfowl (Frederickson and Reid, 1990). In addition, ¯ooding of soil during the growing season induces rapid stomatal closure in many woody plants (Pereira and Kozlowski, 1997; Kozlowski, 1980a,b, 1982b, 1997; Tang and Kozlowski, 1982b,c; Pezeshki and Chambers, 1985), thereby preventing absorption of gaseous air pollutants and reducing pollution damage (Norby and Kozlowski, 1983). Closure of stomata of ¯ooded plants has been attributed to hormonal signals transmitted from roots to leaves (Zhang and Davies, 1990; Else et al., 1996). Flooding also protects wetlands, resets ecosystem trajectories, and in¯uences decomposition of organic matter and nutrient cycling. Furthermore, ¯ooding often maintains high diversity of riparian forests, supplies mineral nutrients, and transports sediments needed for maintenance of downstream ecosystems (Bayley, 1995; Postel and Carpenter, 1997; Haeuber and Michener, 1998; Yarie et al., 1998). Early installation of dams and levees was based largely on reducing variability in water supplies and channel positions of rivers (Sparks et al., 1998). Unfortunately the elimination of natural ¯ooding regimes caused some irreversible and undesirable downstream results. Preoccupation with bene®cial effects of dam construction along rivers often obscured some harmful effects such as loss of species and declining biodiversity (Dudgeon, 2000). Decreased downstream groundwater leads to inhibited regeneration of pioneer species and mortality of mature trees (Stromberg et al., 1996; Rosenberg et al., 2000). Arrested plant regeneration typically alters the course of succession to less productive communities (Nilsson and Berggren, 2000). In Alberta, Canada, a decrease in Populus angustifolia, P. balsamifera, and P. deltoides was attributed to downstream drought following river regulation (Rood et al., 1994). In Australia mortality of Eucalyptus largi¯orens was associated with greatly increased downstream salinization due to reduced ¯ooding frequency in the Murray River (Jolly et al., 1993). Reexamination of early ¯ood management plans led to realization of a need for preserving forested ¯oodplains which depend on an annual T.T. Kozlowski / Forest Ecology and Management 158 (2002) 195±221 advance and recession of ¯oods (Bayley, 1995). Conservation of biodiversity will require preservation of the remaining intact forested ¯oodplains and fostering of more natural ¯ooding disturbances (Michener et al., 1998; Toth et al., 1998). The complexities of the effects of ¯ooding on different ecosystems and interactions with land use point up a need for integrated approaches to balance ecologically bene®cial and socially unacceptable effects of ¯ooding. Cooperation of interdisciplinary teams from biological, physical, and social sciences may be essential to develop holistic plans for managing ¯oods (Michener and Haeuber, 1998; Swanson et al., 1998). The effects of ®re on forested ecosystems range from disastrous to bene®cial. Harmful effects include changes in physical, chemical, and biological properties of soils (e.g. reduction in water holding capacity; soil compaction; soil erosion; loss of mineral nutrients by volatilization, convection, and leaching; destruction of plants; changes in species composition by inhibiting plant succession, and increasing pollution) (Kozlowski and Ahlgren, 1974; Chandler et al., 1983; Pyne, 1984; Pyne et al., 1996; Kozlowski and Pallardy, 1997b). Over the years forest management objectives have evolved from completely excluding ®re to tolerating many natural ®res because of their importance in perpetuating forests. However, many catastrophic forest ®res also emphasized a need for incorporating prescribed burning in forest management planning. Much interest has been shown in such bene®ts of prescribed burning as removal of accumulated fuels (thereby preventing catastrophic ®res), increase in water yield, control of insects and diseases, preparation of seedbeds, and release of seeds from serotinous cones (Kayll, 1974; Chandler et al., 1983; Biswell, 1989). Burning of peat greatly improved seedbeds and regeneration of P. mariana stands (Chrosciewicz, 1976). Both N mineralization and nitri®cation in the forest ¯oor of a P. ponderosa stand were increased by prescribed burning (White, 1986). Use of prescribed burning requires knowledge of ®re ecology, experience, and very competent supervision (Biswell, 1989). 1. Genetic engineering: studies of effects of gene transfer from one species to another on resistance 2. 3. 4. 5. 211 of plants to insects, diseases, biocides, and environmental stresses (Fillatti et al., 1987, 1988; McCown et al., 1991; Hamerschlag and Litz, 1992; Kozlowski and Pallardy, 1997b). Potential effects of global warming: mechanisms by which temperature increases may in¯uence physiology and growth of forest ecosystems (Mooney, 1991); determination of interactive effects of CO2 and other climatic variables on productivity of forest ecosystems (Norby et al., 1996); effects of exposure of large forest ecosystems to elevated CO2 on canopy development, below-ground processes, and interactions with other environmental factors and stresses (Hendrey, 1992; Mauney et al., 1992; Rogers et al., 1992; Kozlowski, 2000). Agroforestry systems: studies on how spatial and temporal arrangements of plants affect resource pools as a basis for selecting species and genotypes that will maximize sharing of resources and sustain high yields of harvested products (Huxley, 1985, 1987; Brewbaker, 1987; Nair, 1989; Owino, 1996; Rhoads, 1996±1997); physiological interactions among herbaceous and woody plants that will optimize use of radiant energy, water, and mineral nutrients (Kozlowski and Huxley, 1983; Huxley, 1987, 1996; Sanchez, 1995; Nair, 1998). Modeling: construction of models to estimate stand productivity; calculation of ¯ows of carbon, water, and mineral nutrients through forest ecosystems (Landsberg and Gower, 1997). Models may be useful in dealing with complex processes in forest stands and in better understanding the impacts of the factors that in¯uence growth and development of forest ecosystems (O'Hara and Vallapil, 1995, 1999; Kaufmann and Linder, 1996; Dale and Van Winkle, 1998; Koltenberg and O'Hara, 1999; O'Hara et al., 1999). Remote sensing: monitoring of spectral signatures to quantify injury to forest ecosystems (Skole and Tucker, 1993; Holmgren and Thuresson, 1998). Acknowledgements The valuable assistance of Pavel and Joy SÏvihra in manuscript preparation is gratefully acknowledged. 212 T.T. Kozlowski / Forest Ecology and Management 158 (2002) 195±221 References Abrams, M.D., 1988. Sources of variation in osmotic potentials with special reference to North American tree species. For. Sci. 34, 1030±1046. Ahlgren, C.E., 1974. Effects of ®re on temperate forests: northcentral United States. In: Kozlowski, T.T., Ahlgren, C.E. (Eds.), Fire and Ecosystems. Academic Press, New York, NY, USA, pp. 279±319. Anderson, J.M., Spencer, T., 1991. Carbon, nutrient and water balances of tropical rain forest ecosystems subject to disturbance: management implications and research proposals. Man Biosphere Digest, Vol. 7. UNESCO, Paris, France. Atkinson, D., Johnson, M.G., 1979. The effect of orchard soil management on the uptake of nitrogen by established apple trees. Sci. Food Agric. 30, 129±135. Aussenac, G., Granier, A., 1988. Effects of thinning on water stress and growth in Douglas-®r. Can. J. For. Res. 18, 100±105. Ayers, J.C., Barden, J.A., 1975. Net photosynthesis and dark respiration of apple leaves as affected by pesticides. J. Am. Soc. Hortic. Sci. 100, 24±28. Bachelard, E.F., Sands, R., 1968. Effect of weedicides on starch content and coppicing of cut stumps in manna gum. Aust. For. 32, 49±54. Bamber, R.K., Humphreys, F.R., 1965. Variations in sapwood starch levels in some Australian forest species. Aust. For. 29, 15±23. Barbera, G., Fatta del Bosco, G., LoCascio, B., 1985. Effects of water stress on lemon summer bloom: the ``Forzatura'' technique in the Sicilian citrus industry. Acta Hortic. 171, 391±397. Barker, J.R., Tingey, D.T., 1992. The effects of air pollution on biodiversity: a synopsis. In: Barker, J.R., Tingey, D.T. (Eds.), Air Pollution Effects on Biodiversity. Van Nostrand Reinhold, New York, NY, USA, pp. 3±9. Barnes, R.L., 1972. Effects of chronic exposures to ozone on photosynthesis and respiration of pines. Environ. Pollut. 3, 133±138. Battaglia, M., 1989. Seed germination physiology of Eucalyptus delegatensis R.T. Baker in Tasmania. Aust. J. Bot. 41, 119± 136. Bayley, P.B., 1995. Understanding large river±¯oodplain ecosystems. BioScience 45, 153±158. Bazzaz, F.A., 1984. Dynamics of wet tropical forests and their species strategies. In: Medina, E., Mooney, H.A., VazquezYanes, C. (Eds.), Physiological Ecology of Plants of the Wet Tropics. Junk, The Hague, The Netherlands, pp. 233±243. Bell, T.I.W., 1968. Effect of fertilizer and density pretreatment on spruce seedling survival and growth. For. Rec. 67, 1±67. Benwell, A.S., 1998. Post-®re seedling recruitment in coastal heathland in relation to regeneration strategy and habitat. Aust. J. Bot. 46, 75±101. Bewley, J.D., 1994. Seeds: Physiology of Development and Germination, 2nd Edition. Plenum Press, New York, USA. Biswell, H.H., 1974. Effects of ®re on chaparral. In: Kozlowski, T.T., Ahlgren, C.E. (Eds.), Fire and Ecosystems. Academic Press, New York, NY, USA, pp. 321±364. Biswell, H.H., 1989. Prescribed Burning in California Wildlands Vegetation Management. University of California Press, Berkeley, CA, USA. Bonan, G.B., 1989. Environmental factors and ecological processes controlling vegetation patterns in boreal forests. Landsc. Ecol. 3, 111±130. Bossel, H., 1991. Modeling forest dynamics: moving from description to explanation. For. Ecol. Manage. 42, 129±142. Botkin, D.B., Janak, J.F., Wallis, J.R., 1972. Some ecological consequences of a computer model of forest growth. J. Ecol. 60, 849±872. Boyle, J.R., 1975. Nutrients in relation to intensive culture of forest crops. Iowa State J. Res. 49, 297±303. Bradbeer, J.W., 1988. Seed Dormancy and Germination. Chapman & Hall, New York, NY, USA. Braun, E.L., 1950. Deciduous Forests of Eastern North America. McGraw-Hill, New York, NY, USA. Brewbaker, J.L., 1987. Signi®cant nitrogen ®xing trees in agroforestry systems. In: Gholz, H.L. (Ed.), Agroforestry: Realities, Possibilities and Potential. Martinus Nijhoff, Dordrecht, The Netherlands, pp. 31±45. Buckley, R.C., 1982. Seed size and seedling establishment in tropical arid dunecrest plants. Biotropica 14, 314±315. Carlson, R.W., 1979. Reduction in photosynthetic rate of Acer, Quercus, and Fraxinus species caused by sulphur dioxide and ozone. Environ. Pollut. 18, 159±170. Cassel, D.K., 1983. Effects of soil characteristics and tillage practices on water storage and its availability to plant roots. In: Raper, C.D., Kramer, P.J. (Eds.), Crop Reactions to Water and Temperature Stresses in Humid Temperate Climates. Westview Press, Boulder, CO, USA, pp. 167±186. Catovsky, S., Bazzaz, F.A., 2000. The role of resource interactions and seedling regeneration in maintaining a positive feedback in hemlock stands. J. Ecol. 88, 100±112. Cattelino, P.J., Noble, I.R., Slatyer, R.O., Ressell, S.R., 1979. Predicting the multiple pathways of plant succession. Environ. Manage. 3, 41±50. Chalmers, D.J., Olson, K.A., Jones, T.R., 1983. Water relations of peach trees and orchards. In: Kozlowski, T.T. (Ed.), Water De®cits and Plant Growth, Vol. 7. Academic Press, New York, NY, USA, pp. 197±232. Chalmers, D.J., Mitchell, P.D., Jerie, P.H., 1984. The physiology of growth of peach and pear trees using reduced irrigation. Acta Hortic. 146, 143±149. Chandler, C., Cheney, P., Thomas, P., Trabaud, L., Williams, D., 1983. Fire in Forestry, Vol. 1. Forest Fire Behavior and Effects. Wiley, New York, NY, USA. Chapin III, F.S., Sala, O.E., Burke, I.C., Grime, P., et al., 1998. Ecosystem consequences of changing biodiversity. BioScience 48, 45±52. Chazdon, R.L., Pearcy, R.W., 1986. Photosynthetic responses to light variation in rain forest species. II. Carbon gain and light utilization during sun¯ecks. Oecologia 69, 524±531. Chazdon, R.L., Pearcy, R.W., 1991. The importance of sun¯ecks for forest understory plants. BioScience 41, 760±766. Ching, T.M., Ching, K.K., 1962. Physical and physiological changes in maturing Douglas-®r cones and seeds. For. Sci. 8, 21±31. T.T. Kozlowski / Forest Ecology and Management 158 (2002) 195±221 Christensen, N.L., 1995. Fire ecology. In: Nierenberg, W.A. (Ed.), Encyclopedia of Environmental Biology, Vol. 2. Academic Press, San Diego, CA, USA, pp. 21±32. Chrosciewicz, A., 1976. Burning for black spruce regeneration on a lowland cutover site in southeast Manitoba. Can. J. For. Res. 6, 179±186. Clark, F.B., Liming, F.G., 1953. Sprouting of blackjack oak in the Missouri Ozarks. US For. Serv., Cent. States For. Exp. Stn. Tech. Pap. 137. Clemens, J., Jones, P.G., 1978. Modi®cation of drought resistance by water stress conditioning in Acacia and Eucalyptus. J. Exp. Bot. 29, 895±904. Clemens, J., Campbell, L.C., Nurisjah, S., 1983. Germination, growth and mineral ion concentration of Casuarina species under saline conditions. Aust. J. Bot. 31, 1±9. Cole, E.C., Newton, M., 1986. Nutrient, moisture, and light relations in 5-year-old Douglas-®r plantations under variable competition. Can. J. For. Res. 16, 727±732. Conard, S.G., Radosevich, S.R., 1982. Growth responses of white ®r to decreased shading and root competition by montane chaparral shrubs. For. Sci. 28, 309±320. Connell, J.H., Slatyer, R.O., 1977. Mechanisms of succession in natural communities and their role in community stability and organization. Am. Nat. 111, 1119±1144. Connor, D.J., 1983. Plant stress factors and their in¯uence on production of agroforestry plant associations. In: Huxley, P.A. (Ed.), Plant Research and Agroforestry. Pillans and Wilson, Edinburgh, Scotland, pp. 401±426. Constantinidou, H.A., Kozlowski, T.T., 1979a. Effects of sulfur dioxide and ozone on Ulmus americana seedlings. I. Visible injury and growth. Can. J. Bot. 47, 170±175. Constantinidou, H.A., Kozlowski, T.T., 1979b. Effects of sulfur dioxide and ozone on Ulmus americana seedlings. II. Carbohydrates, proteins, and lipids. Can. J. Bot. 57, 176±184. Constantinidou, H.A., Kozlowski, T.T., Jensen, K., 1976. Effects of sulfur dioxide on Pinus resinosa seedlings in the cotyledon stage. J. Environ. Qual. 5, 141±146. Coyne, P.I., Bingham, G.E., 1982. Variation in photosynthesis and stomatal conductance in an ozone-stressed ponderosa pine stand: light response. For. Sci. 28, 257±273. Crawley, M.J., 1983. Herbivory: The Dynamics of Animal±Plant Interactions. University of California Press, Berkeley, CA, USA. Critch®eld, W.B., 1957. Geographic variation in Pinus contorta. Maria Moors Cabot Found. Publ. 3. Currie, J.A., 1984. Gas diffusion through soil crumbs: the effects of compaction and wetting. J. Soil Sci. 35, 1±10. Dale, D.V., Doyle, T.W., Shugart, H.H., 1985. A comparison of tree growth models. Ecol. Model. 29, 145±169. Dale, V.H., Van Winkle, W., 1998. Models provide understanding, not belief. Bull. Ecol. Soc. Am. 79, 169±170. Darley-Hill, S., Johnson, W.C., 1981. Acorn dispersal by the blue jay (Cyanocitta cristata). Oecologia 50, 231±232. Dasgupta, P., Levin, S., Lubchenko, J., 2000. Economic pathways to ecological stability. BioScience 50, 339±345. Davenport, D.C., Uriu, K., Martin, P.E., Hagan, R.M., 1972. Antitranspirants increase size, reduce shrivel of olive fruits. Calif. Agric. 26 (7), 6±8. 213 Davies, W.J., Kozlowski, T.T., 1975. Effects of applied abscisic acid and silicone on water relations and photosynthesis of woody plants. Can. J. For. Res. 5, 90±96. Davies, W.J., Kozlowski, T.T., Lee, K.S., 1974. Stomatal characteristics of Pinus resinosa and Pinus strobus in relation to transpiration and antitranspirant ef®ciency. Can. J. For. Res. 4, 571±574. Day, K.R., Leather, S.R., 1997. Threats to forestry by insect pests in Europe. In: Watt, A.D., Stark, N.E., Hunter, M.D. (Eds.), Forests and Insects. Chapman & Hall, London, UK, pp. 177± 205. DeBell, D.S., Naylor, A.W., 1984. Some factors affecting germination of swamp tupelo seeds. Ecology 53, 504±506. DeCastro, M.F.-G., Martinez-Honduvilla, C.J., 1984. Ultrastructural changes in naturally aged Pinus pinea seeds. Physiol. Plant. 62, 581±588. Dekker-Robertson, D.L., Libby, W.J., 1998. American forest policy-global ethical tradeoffs. BioScience 48, 471±477. Dick, M., 1998. Pine pitch cankerÐthe threat to New Zealand. N.Z. For. 42, 30±34. Dickmann, D.I., Stuart, K.W., 1983. The Culture of Poplars. Department of Forestry, Michigan State University, East Lansing, MI, USA. Ding, Y.-X., Chen, J.-L., 1995. Effect of continuous plantation of Chinese ®r on soil fertility. Pedosphere 5, 57±66. Donner, S.L., Running, S.W., 1986. Water stress response after thinning Pinus contorta stands in Montana. For. Sci. 32, 614± 625. Dudgeon, D., 2000. Large-scale hydrological changes in tropical Asia: prospects for riverine biodiversity. BioScience 50, 793± 806. Eckert, R.T., Houston, D.B., 1980. Photosynthesis and needle elongation response of Pinus strobus clones to low level sulphur dioxide exposure. Can. J. For. Res. 10, 357±361. Elliott, K.J., White, A.S., 1987. Competitive effects of various grasses and forbs on ponderosa pine seedlings. For. Sci. 33, 356±366. Else, M.A., Tiekstra, A.E., Croker, S.J., Davies, W.J., Jackson, M.B., 1996. Stomatal closure in ¯ooded tomato plants involves abscisic acid and a chemically unidenti®ed anti-transpirant in xylem sap. Plant Physiol. 112, 239±247. Evans, J., 1992. Plantation Forestry in the Tropics: Tree Planting for Industrial, Social, Environmental and Agroforestry Purposes, 2nd Edition. Clarendon Press, New York, NY, USA. Ewel, J.J., Mazzarino, M.J., Barish, C.W., 1991. Tropical soil fertility changes under monocultures and successional communities of different structure. Ecol. Appl. 1, 289±302. Facelli, J.M., Pickett, V., 1991. Plant litter: its dynamics and effects on plant community structure. Bot. Rev. 57, 1±32. FAO, 1997. State of the World's Forests. Food and Agriculture Organization of the United Nations. Rome, Italy. Fearnside, P., 1996. Amazonian deforestation and global warming: carbon stocks in vegetation replacing Brazil's Amazon forest. For. Ecol. Manage. 80, 21±34. Feller, M.C., 1978. Nutrient movement in soils beneath eucalypt and exotic conifer forests in southern central Victoria. Aust. J. Ecol. 3, 357±372. 214 T.T. Kozlowski / Forest Ecology and Management 158 (2002) 195±221 Ferguson, I.S., 1996. Sustainable Forest Management. Oxford University Press, Oxford. Fillatti, J.J., Selmer, J., McCown, B., Haissig, B., Comai, L., 1987. Agrobacterium-mediated transformation and regeneration of Populus. Mol. Gen. Genet. 206, 192±199. Fillatti, J.J., Haissig, B., McCown, B., Comai, L., Riemenschneider, D., 1988. Development of glyphosate-tolerant Populus plants through expression of mutant aroA gene from Salmonella typhimurium. In: Hanover, J.W., Keathley, D.E. (Eds.), Genetic Manipulation of Woody Plants. Plenum Press, New York, NY, USA, pp. 243±250. Franklin, J.F., 1987. Importance and justi®cation of long-term studies in ecology. In: Likens, G.E. (Ed.), Long-Term Studies in Ecology. Springer, New York, NY, USA, pp. 3±19. Franklin, J.F., 1993. Preserving biodiversity: species, ecosystems, or landscapes. Ecol. Appl. 3, 202±205. Frederickson, L.H., Reid, F.A., 1990. Impacts of hydrologic alteration of management of freshwater wetlands. In: Sweeney, M. (Ed.), Management of Dynamic Ecosystems. Wildlife Society, West Lafayette, IN, USA, pp. 72±90. Friend, A.A., Shugart, H.H., Running, S.W., 1993. A physiologybased gap model of forest dynamics. Ecology 74, 792± 797. Fuller, J.L., Foster, D.R., McLachlan, J.S., Drake, D., 1998. Impact of human activity on regional forest composition and dynamics in central New England. Ecosystems 1, 76±95. Gashwiler, J.S., 1967. Conifer seed survival in a western Oregon clearcut. Ecology 48, 431±438. Gill, A.M., 1981. Fire adaptive traits of vascular plants. US For. Serv. Gen. Tech. Rep. WO 26, pp. 208±230. Gill, A.M., Groves, R.H., 1981. Fire regimes in heathlands and their plant ecologic effects. In: Specht, R.L. (Ed.), Ecosystems of the World, Vol. 9B. Heathlands and Related Shrublands. Elsevier, Amsterdam, The Netherlands, pp. 61± 84. Gordon, J.C., 1996. Trends and developments in modern forestry. In: McDonald, P., Lassoic, J. (Eds.), The Literature of Forestry and Agroforestry. Cornell University Press, Ithaca, NY, USA, pp. 1±14. Greacen, E.L., Sands, R., 1980. Compaction of forest soils: a review. Aust. J. Soil Res. 18, 163±189. Guries, R.P., 1995. Forest genetics. In: Nierenberg, W.A. (Ed.), Encyclopedia of Environmental Biology, Vol. 3. Academic Press, San Diego, CA, USA, pp. 105±108. Haeuber, R.A., Michener, W.K., 1998. Policy implications of recent natural and managed ¯oods. BioScience 48, 765±772. Hall, J.B., Swaine, M.D., 1980. Seed stocks in Ghanaian forest soils. Biotropica 12, 256±263. Hamerschlag, F.A., Litz, RE. (Eds.), 1992. Biotechnology of Perennial Fruit Crops. CAB International, Wallingford, UK. Han, Q., Yamaguchi, E., Odaka, N., Kakubari, Y., 1999. Photosynthetic induction responses to variable light under ®eld conditions in three species grown in the gap and understory of a Fagus crenata forest. Tree Physiol. 19, 625±634. Hanes, T.L., 1988. California chaparral. In: Barbour, M.G., Major, J. (Eds.), Terrestrial Vegetation of California. Wiley, New York, NY, USA, pp. 417±469. Harbinson, J., Woodward, F.I., 1984. Field measurements of the gas exchange of woody plant species in simulated sun¯ecks. Ann. Bot. 53, 841±851. Harrington, J.F., 1972. Seed storage and longevity. In: Kozlowski, T.T. (Ed.), Seed Biology, Vol. 3. Academic Press, New York, NY, USA, pp. 145±245. Hart, J.W., 1988. Light and Plant Growth. Unwin Hyman, London, UK. Haynes, R.J., Goh, K.M., 1980. Seasonal levels of available nutrients under grassed-down, cultivated and zero-tilled orchard soil management practices. Aust. J. Soil Res. 18, 363±373. Heath, R.L., 1980. Initial events in injury to plants by air pollutants. Ann. Rev. Plant Physiol. 31, 395±489. Hendrey, G.R., 1992. The DOE/USDA FACE program: goal objectives and results through 1989. Crit. Rev. Plant Sci. 11, 75±83. Hett, J.M., Loucks, O.L., 1971. Sugar maple (Acer saccharum Marsh.) seedling mortality. J. Ecol. 59, 507±520. Hoffmann, W.A., Bazzaz, F.A., Chatterton, N.J., Harrison, P.A., Jackson, R.B., 2000. Elevated CO2 enhances resprouting of a tropical savanna tree. Oecologia 123, 312±317. Holmgren, P., Thuresson, T., 1998. Satellite remote sensing for forestry planningÐa review. Scand. J. For. Res. 13, 90±110. Horn, R., Domzal, H., Slowinska-Jurkiewicz, A., Van Ouwerkerk, C., 1995. Soil compaction processes and their effects on the structure of arable soils and the environment. Soil Tillage Res. 35, 23±36. Houghton, R.A., 1995. Deforestation. In: Nierenberg, W.A. (Ed.), Encyclopedia of Environmental Biology, Vol. 1. Academic Press, San Diego, CA, USA, pp. 449±461. Houghton, R.A., 1998. Historic role of forests in the global carbon cycle. In: Kohlmaier, G.H., Weber, M., Houghton, R.A. (Eds.), Carbon Dioxide Mitigation in Forestry and Wood Industry. Springer, Berlin, pp. 1±24. Houghton, R.A., Skole, D.L., Lefkowitz, D.S., 1991. Changes in the landscape of Latin America between 1850 and 1855. II. Net release of CO2 to the atmosphere. For. Ecol. Manage. 38, 173± 199. Huang, J., Lacy, S.T., Ryan, P.J., 1996. Impact of forest harvesting on the hydraulic properties of surface soil. Soil Sci. 161, 79±86. Hunter, A.F., Aarssen, L.W., 1988. Plants helping plants. BioScience 38, 34±40. Huston, M.A., 1991. Use of individual-based forest successional models to link physiological whole-tree models to landscapescale ecosystem models. Tree Physiol. 9, 293±306. Hutchinson, B.A., Matt, D.R., 1977. The distribution of solar radiation within a deciduous forest. Ecol. Monogr. 47, 185± 207. Huxley, P.A., 1985. The tree-crop interface or simplifying the biological/environmental study of mixed cropping agroforestry systems. Agrofor. Syst. 5, 251±275. Huxley, P.A., 1987. Agroforestry experimentation: separating the wood from the trees? Agrofor. Syst. 5, 251±275. Huxley, P.A., 1996. Woody±non-woody plant mixtures: some afterthoughts. In: Ong, C.K., Huxley, P.A. (Eds.), Tree±Crop Interactions: A Physiological Approach. CAB International, Wallingford, UK, pp. 365±376. T.T. Kozlowski / Forest Ecology and Management 158 (2002) 195±221 HytoÈnen, J., 1992. Allelopathic potential of peatland plant species on germination and growth of Scots pine, silver birch and downy birch. Silva Fenn. 26, 63±73. Jackson, G.A.D., Blundell, J.B., 1963. Germination in Rosa. J. Hortic. Sci. 38, 310±320. Jacobs, M.R., 1955. Growth Habits of the Eucalypts. For. Timber Bur., Australia, pp. 1±262. Jim, C.Y., 1993. Soil compaction as a constraint to tree growth in tropical and subtropical urban habitats. Environ. Conserv. 20, 35±49. Jolly, I.D., Walker, G.R., Thornburg, P.J., 1993. Salt accumulation in semiarid ¯ood plain soils with implications for forest health. J. Hydrol. 150, 589±614. Jones, L., 1961. Effects of light on germination of forest tree seeds. Proc. Int. Seed Test. Assoc. 26, 437±452. Jones, R.H., Sharitz, R.R., Dixon, P.M., Segal, D.S., Schneider, R.L., 1994. Woody plant regeneration in four ¯ood plain forests. Ecol. Monogr. 64, 345±367. Jordan, C.F., 1985. Nutrient Cycling in Tropical Forest Ecosystems. Wiley, New York, NY, USA. Kang, B.T., Lal, R., 1981. Nutrient losses in water runoff from agricultural catchments. In: Lal, R., Russel, E.W. (Eds.), Wiley, New York, NY, USA, pp. 153±161. Kaufman, P.B., Cseke, L.J., Warber, S., Duke, A.J., Brielman, H.L., 1999. Natural Products from Plants. CRC Press, Boca Raton, FL, USA. Kaufmann, M.R., 1969. Effects of water potential on germination of lettuce, sun¯ower, and citrus seed. Can. J. Bot. 47, 1761± 1764. Kaufmann, M.R., Eckard, A.N., 1977. Water potential and temperature effects on germination of Engelmann spruce and lodgepole pine seeds. For. Sci. 23, 27±33. Kaufmann, M.R., Linder, S., 1996. Tree physiology research in a changing world. Tree Physiol. 16, 1±4. Kayll, A.J., 1974. Use of ®re in land management. In: Kozlowski, T.T., Ahlgren, C.E. (Eds.), Fire and Ecosystems. Academic Press, New York, NY, USA, pp. 483±511. Keane, R.E., Ryan, K.C., Running, S.W., 1996. Simulating effects of ®re on northern Rocky Mountain landscapes with the ecological process model FIRE-BGC. Tree Physiol. 16, 319±331. Keay, R.W.J., 1957. Wind-dispersed species in a Nigerian forest. J. Ecol. 45, 471±478. Keeves, A., 1996. Some evidence of loss of productivity with successive rotation of Pinus radiata in the southeast of S. Australia. Aust. For. 30, 51±63. Keller, T., 1983. Air pollutant deposition and effects on plants. In: Ulrich, B., Pankrath, J. (Eds.), Accumulation of Air Pollutants in Forest Ecosystems. Reidel, Dordrecht, The Netherlands, pp. 285±294. Khan, A.A., Samimy, C., 1982. Hormones in relation to primary and secondary seed dormancy. In: Khan, A.A. (Ed.), The Physiology and Biochemistry of Seed Development, Dormancy and Germination. Elsevier, Amsterdam, The Netherlands, pp. 203±241. Khan, M.A., Ungar, I.A., 1984. Seed polymorphism and germination responses to salinity stress in Atriplex triangularis Willd. Bot. Gaz. 145, 487±494. 215 Koller, D., 1972. Environmental control of seed dormancy. In: Kozlowski, T.T. (Ed.), Seed Biology, Vol. 2. Academic Press, New York, NY, USA, pp. 1±101. Koltenberg, C.S., O'Hara, K.L., 1999. Leaf area and tree increment dynamics of even-aged and multiaged lodgepole pine stands in Montana. Can. J. For. Res. 29, 687±695. Komarek, E.V., 1974. Effects of ®re on temperate forests and related ecosystems in southeastern United States. In: Kozlowski, T.T., Ahlgren, C.E. (Eds.), Fire and Ecosystems. Academic Press, New York, NY, USA, pp. 251±277. Korol, R.L., Running, S.W., Milner, K.S., 1995. Incorporating intertree competition into an ecosystem model. Can. J. For. Res. 25, 413±424. Korol, R.L., Milner, K.S., Running, S.W., 1996. Testing a mechanistic model for predicting stand and tree growth. For. Sci. 42, 139±153. Kozlowski, T.T. (Ed.), 1968. Water De®cits and Plant Growth, Vol. 2. Plant Water Consumption and Response. Academic Press, New York, NY, USA. Kozlowski, T.T., 1971. Growth and Development of Trees, Vol. 1. Seed Germination, Ontogeny and Shoot Growth. Academic Press, New York, NY, USA. Kozlowski, T.T., 1972. Physiology of water stress. In: Wildland Shrubs: Their Biology and Utilization. USDA For. Serv. Gen. Tech. Rep. INT-l, pp. 229±244. Kozlowski, T.T., 1976. Drought resistance and transplantability of shade trees. USDA For. Serv. Gen. Tech. Rep. NE-22, pp. 77± 90. Kozlowski, T.T., 1979. Tree Growth and Environmental Stresses. University of Washington Press, Seattle, WA, USA. Kozlowski, T.T., 1980a. Impacts of air pollution on forest ecosystems. BioScience 30, 88±93. Kozlowski, T.T., 1980b. Responses of shade trees to pollution. J. Arboric. 6, 29±41. Kozlowski, T.T., 1982a. Water supply and tree growth. Part I. Water de®cits. For. Abstr. 43, 57±95. Kozlowski, T.T., 1982b. Water supply and tree growth. Part II. Flooding. For. Abstr. 43, 145±161. Kozlowski, T.T., 1983. Reduction in yield of forest and fruit trees by water and temperature stress. In: Raper, C.D., Kramer, P.J. (Eds.), Crop Reactions to Water and Temperature Stresses in Humid, Temperate Climates. Westview Press, Boulder, CO, USA, pp. 67±88. Kozlowski, T.T., 1984a. Extent, causes, and impacts of ¯ooding. In: Kozlowski, T.T. (Ed.), Flooding and Plant Growth. Academic Press, New York, NY, USA, pp. 1±7. Kozlowski, T.T., 1984b. Responses of woody plants to ¯ooding. In: Kozlowski, T.T. (Ed.), Flooding and Plant Growth. Academic Press, New York, NY, USA, pp. 129±164. Kozlowski, T.T., 1984c. Plant responses to ¯ooding of soil. BioScience 34, 162±167. Kozlowski, T.T., 1985a. Soil aeration, ¯ooding and tree growth. J. Arboric. 1, 85±96. Kozlowski, T.T., 1985b. Effect of direct contact of Pinus resinosa seeds and young seedlings with N-dimethylaminosuccinamic acid, 2-chloroethyl-trimethylammonium chloride, or maleic hydrazide. Can. J. For. Res. 15, 1000±1004. 216 T.T. Kozlowski / Forest Ecology and Management 158 (2002) 195±221 Kozlowski, T.T., 1985c. Effects of SO2 on plant community structure. In: Winner, W.E., Mooney, H.A., Goldstein, R. (Eds.), Sulfur Dioxide and Vegetation. Physiology, Ecology, and Policy Issues. Stanford University Press, Stanford, CA, pp. 431±451. Kozlowski, T.T., 1985d. Measurement of effects of environmental and industrial chemicals on terrestrial plants. In: Vouk, V.B., Butler, G.C., Hoel, D.G., Peakall, D.B. (Eds.), Methods for Estimating Risk of Chemical Injury: Human and Non-Human Biota and Ecosystems, Scope 35. Wiley, Chichester, pp. 573± 609. Kozlowski, T.T., 1986a. Effects on seedling development of direct contact of Pinus resinosa seeds or young seedlings with Captan. Eur. J. For. Pathol. 16, 87±90. Kozlowski, T.T., 1986b. The impact of environmental pollution on shade trees. J. Arboric. 12, 29±37. Kozlowski, T.T., 1986c. Effect of 2,3,6-TBA on seed germination, early development and mortality of Pinus resinosa seedlings. Eur. J. For. Path. 7, 385±390. Kozlowski, T.T., 1992. Carbohydrate sources and sinks in woody plants. Bot. Rev. 58, 107±222. Kozlowski, T.T., 1995. Physiological ecology of forest stands. In: Nierenberg, W.A. (Ed.), Encyclopedia of Environmental Biology, Vol. 3. Academic Press, San Diego, CA, USA, pp. 81±91. Kozlowski, T.T., 1996. Re¯ections on research and editing. In: McDonald, P., Lassoie, J. (Eds.), The Literature of Forestry and Agroforestry. Cornell University Press, Ithaca, NY, USA, pp. 198±235. Kozlowski, T.T., 1997. Responses of woody plants to ¯ooding and salinity. http://www.heronpublishing.com/tp/monograph/kozlowski.pdt. Kozlowski, T.T., 1999. Soil compaction and growth of woody plants. Scand. J. For. Res. 14, 596±619. Kozlowski, T.T., 2000. Responses of woody plants to humaninduced environmental stresses: issues, problems and strategies for alleviating stress. Crit. Rev. Plant Sci. 19, 91±170. Kozlowski, T.T., Ahlgren, C.E. (Eds.), 1974. Fire and Ecosystems. Academic Press, New York, NY, USA. Kozlowski, T.T., Clausen, J.J., 1970. Effect of decenylsuccinic acid on needle moisture content and shoot growth of Pinus resinosa. Can. J. Plant Sci. 50, 355±358. Kozlowski, T.T., Constantinidou, H.A., 1986a. Responses of woody plants to environmental pollution. Part I. Sources, types of pollutants, and plant responses. For. Abstr. 47, 5±51. Kozlowski, T.T., Constantinidou, H.A., 1986b. Responses of woody plants to environmental pollution. Part II. Factors affecting responses to pollution. For. Abstr. 47, 105±132. Kozlowski, T.T., Huxley, P.A., 1983. The role of controlled environments in agroforestry research. In: Huxley, P.A. (Ed.), Plant Research and Agroforestry. Pillans and Wilson, Edinburgh, Scotland, pp. 551±567. Kozlowski, T.T., Keller, T., 1966. Food relations of woody plants. Bot. Rev. 32, 293±381. Kozlowski, T.T., Keller, T., 1968. A short review of the effects of fungicides on photosynthesis in woody plants. Pest Articles and News Summaries (Sect. B) 14, 31±35. Kozlowski, T.T., Kuntz, J.E., 1963. Effects of simazine, atrazine, propazine, and eptam on growth of pine seedlings. Soil Sci. 95, 164±174. Kozlowski, T.T., Pallardy, S.G., 1984. Effect of ¯ooding on water, carbohydrate, and mineral relations. In: Kozlowski, T.T. (Ed.), Flooding and Plant Growth. Academic Press, Orlando, FL, USA, pp. 145±193. Kozlowski, T.T., Pallardy, S.G., 1997a. Physiology of Woody Plants, 2nd Edition. Academic Press, San Diego, CA, USA. Kozlowski, T.T., Pallardy, S.G., 1997b. Growth Control in Woody Plants. Academic Press, San Diego, CA, USA. Kozlowski, T.T., Sasaki, S., 1970. Effects of herbicides on seed germination and development of young pine seedlings. In: Proceedings of the International Symposium on Seed Physiology. Poznan, Poland, pp. 19±24. Kozlowski, T.T., Torrie, J.H., 1965. Effect of soil incorporation of herbicides on seed germination and growth of pine seedlings. Soil Sci. 100, 139±144. Kozlowski, T.T., Kramer, P.J., Pallardy, S.G., 1991. The Physiological Ecology of Woody Plants. Academic Press, San Diego, CA, USA. Kozlowski, T.T., Sasaki, S., Torrie, J.H., 1967. In¯uence of temperature on phytotoxicity of triazine herbicides to pine seedlings. Am. J. Bot. 54, 790±796. Kramer, P.J., Boyer, J.S., 1995. Water Relations of Plants and Soils. Academic Press, San Diego, CA, USA. Lamoreaux, R.J., Chaney, W.R., 1978a. The effect of cadmium on net photosynthesis transpiration, and dark respiration of excised silver maple leaves. Physiol. Plant 43, 231±236. Lamoreaux, R.J., Chaney, W.R., 1978b. Photosynthesis and transpiration of excised silver maple leaves exposed to cadmium and sulphur dioxide. Environ. Pollut. 17, 259± 268. Landsberg, J.J., Gower, S.T., 1997. Applications of Physiological Ecology to Forest Management. Academic Press, San Diego, CA, USA. Leck, M.A., 1995. Seed banks. In: Nierenberg, W.J. (Ed.), Encyclopedia of Environmental Biology, Vol. 3. Academic Press, San Diego, CA, USA, pp. 277±293. Leck, M.A., Parker, T., Simpson, R.L. (Eds.), 1989. Ecology of Soil Seed Banks. Academic Press, San Diego, CA, USA. Lee, K.J., Kozlowski, T.T., 1974. Effect of silicone antitranspirants on woody plants. Plant and Soil 40, 493±506. Likens, G.E., 1983. A priority for ecological research. Bull. Ecol. Soc. Am. 64, 234±243. Likens, G.E., 1985. An experimental approach for the study of ecosystems. J. Ecol. 73, 381±396. Likens, G.E. (Ed.), 1987. Long-Term Studies in Ecology: Approaches and Alternatives. Springer, New York, NY, USA. Lindenmayer, D.B., Franklin, J.F., 1997. Managing stand structure as part of ecologically sustainable forest management in Australian mountain ash forests. Conserv. Biol. 11, 1053±1065. Little, S., 1974. Effects of ®re on temperate forests. In: Kozlowski, T.T., Ahlgren, C.E. (Eds.), Fire and Ecosystems. Academic Press, New York, NY, USA, pp. 225±250. Lopez, O.L., Kursar, T.A., 1999. Flood tolerance of four tropical tree species. Tree Physiol. 19, 925±932. T.T. Kozlowski / Forest Ecology and Management 158 (2002) 195±221 Lorenc-Plucinska, G., 1978. Effect of sulphur dioxide on photosynthesis, photorespiration and dark respiration of Scots pine differing in resistance to this gas. Arbor. Kornickie 23, 133± 144. Lorenc-Plucinska, G., 1982. Effect of sulphur dioxide on CO2 exchange in SO2-tolerant and SO2-susceptible Scots pine seedlings. Photosynthetica 16, 140±144. Lorenc-Plucinska, G., 1988. Effect of nitrogen dioxide on CO2 exchange in Scots pine seedlings. Photosynthetica 22, 108±111. Lugo, A.E., Brown, S., 1982. Conversion of tropical moist forests: a critique. Intersciencia 7, 89±93. Lutz, H., 1939. Layering in eastern white pine. Bot. Gaz. 101, 505± 507. Malmer, A., Grip, H., 1990. Soil disturbance and loss of in®ltrability caused by mechanized and manual extraction of tropical rainforest in Sabah, Malaysia. For. Ecol. Manage. 38, 1±12. Manalled, F.D., Kelty, M.J., Ewel, J.J., 1998. Canopy development in tropical tree plantations: a comparison of species mixtures and monocultures. For. Ecol. Manage. 104, 249±263. Marshall, P.E., Kozlowski, T.T., 1974. The role of cotyledons in growth and development of woody angiosperms. Can. J. Bot. 52, 239±245. Marshall, P.E., Kozlowski, T.T., 1976a. Importance of photosynthetic cotyledons for early growth of woody angiosperms. Physiol. Plant. 37, 336±340. Marshall, P.E., Kozlowski, T.T., 1976b. Compositional changes in cotyledons of woody angiosperms. Can. J. Bot. 54, 2473±2479. Marshall, P.E., Kozlowski, T.T., 1977. Changes in structure and function of epigeous cotyledons of woody angiosperms during early seedling growth. Can. J. Bot. 55, 208±215. Mauney, J.R., Lewin, K.F., Hendrey, G.R., Kimball, B.A., 1992. Growth and yield of cotton exposed to free-air CO2 enrichment (FACE). Crit. Rev. Plant Sci. 11, 213±222. Mayer, A.M., Poljakoff-Mayber, A., 1989. The Germination of Seeds, 4th Edition. Pergamon Press, Oxford, UK. Medina, E., 1991. Deforestation in the tropics: evaluation of experiences in the Amazon Basin focusing on atmosphere± forest interactions. In: Mooney, H.A., Medina, E., Schindler, D.W., Schulze, E.-D., Walker, B.H. (Eds.), Ecosystem Experiments, Scope 45. Wiley, Chichester, UK, pp. 23±43. Menzel, C.M., 1983. The control of ¯oral initiation in lychee: a review. Sci. Hortic. 21, 201±215. Menzel, C.M., Simpson, D.R., 1990. Effect of environment on growth and ¯owering of lychee (Litchi chinensis Sonn.). Acta Hortic. 275, 161±166. Mercier, S., Langlois, C.G., 1992. Indices of maturity and storage of white spruce seeds as a function of time of harvesting in Quebec. Can. J. For. Res. 22, 1516±1523. Mexal, J.G., South, D.B., 1991. Bareroot seedling culture. In: Duryea, M.L., Dougherty, P.M. (Eds.), Forest Regeneration Manual. Kluwer Academic Publishers, Dordrecht, The Netherlands, pp. 89±115. McCown, B., McCabe, D.E., Russell, D.R., Robison, D.J., Barton, K.A., Raffa, K.F., 1991. Stable transformation of Populus and incorporation of pest resistance by electric discharge particle acceleration. Plant Cell Rep. 9, 590±594. 217 McNeely, J.A., 1994. Protected areas for the 21st century: working to provide bene®ts to society. Biodivers. Conserv. 3, 390±405. Michener, W.K., Blood, E.R., Box, J.B., Couch, C.A., Golladay, S.W., Hippe, D.J., Mitchell, R.J., Palik, B.J., 1998. Tropical storm ¯ooding of a coastal plain landscape. BioScience 48, 696±705. Michener, W.K., Haeuber, R.A., 1998. Flooding: natural and managed disturbances. BioScience 48, 677±680. Miller, R.C., Scott, W., Hazard, J.W., 1996. Soil compaction and conifer growth after tractor yarding at three coastal Washington locations. Can. J. For. Res. 26, 225±236. Mitchell, P.D., Jerie, P.H., Chalmers, D.J., 1984. The effects of regulated water de®cits on pear tree growth, ¯owering, fruit growth, and yield. J. Am. Soc. Hortic. Sci. 109, 604±606. Mitchell, P.D., Chalmers, D.J., Jerie, P.H., Burge, G., 1986. The use of initial withholding of irrigation and tree spacing to enhance the effect of regulated de®cit irrigation in pear trees. J. Am. Soc. Hortic. Sci. 111, 858±864. Miyanishi, K., Kelman, M., 1986. The role of pine in recruitment of two neotropical savanna shrubs, Miconia albicans and Clidemia sericea. Biotropica 18, 224±230. Mooney, H.A., 1991. Introduction. In: Mooney, H.A., Medina, E., Schindler, D.W., Schuize, E.-D., Walker, B.H. (Eds.), Ecosystem Experiments, Scope 35. Wiley, Chichester, UK, pp. xxi±xxv. Moran, E.F., Brondizio, E., Mausel, P., Wu, Y., 1994. Integrating Amazonian vegetation, land-use, and satellite data. BioScience 44, 329±338. Mudd, J.B., Kozlowski, T.T. (Eds.), 1975. Responses of Plants to Air Pollution. Academic Press, New York, NY, USA. Myers, N., 1996. The Primary Source: Tropical Forests and Our Future. Norton, New York, NY, USA. Nair, P.K.R., 1989. Agroforestry Systems in the Tropics. Kluwer Academic Publishers, Dordrecht, The Netherlands. Nair, P.K.R., 1998. Directions in tropical agroforestry research: past, present and future. Agrofor. Syst. 38, 223±246. Naveh, Z., 1974. Effects of ®re in the Mediterranean region. In: Kozlowski, T.T., Ahlgren, C.E. (Eds.), Fire and Ecosystems. Academic Press, New York, NY, USA, pp. 401±434. Nelson, R.F., Kimes, D.S., Salas, W.A., Routhier, M., 2000. Secondary forest age and tropical forest biomass estimation using thematic mapper imagery. BioScience 50, 419±431. Nepstad, D., Uhl, C., Serrao, E.A., 1990. Surrounding barriers to forest regeneration in abandoned, highly degraded pastures: a case study from Paragorninas, Para, Brazil. In: Anderson, A.B. (Ed.), Alternatives to Deforestation. Columbia University Press, New York, NY, USA, pp. 215±229. Newsome, R.D., Kozlowski, T.T., Tang, Z.C., 1982. Responses of Ulmus americana seedlings to ¯ooding of soil. Can. J. Bot. 60, 1685±1695. Nilsson, M.-C., 1994. Separation of allelopathy and resource competition by the boreal dwarf shrub Empetrum hermaphroditum Hagerup. Oecologia 98, 1±7. Nilsson, C., Berggren, K., 2000. Alterations of riparian ecosystems caused by river regulation. BioScience 50, 783±792. Norby, R.J., Kozlowski, T.T., 1981a. Response of SO2-fumigated Pinus resinosa seedlings to post-fumigation temperature. Can. J. Bot. 59, 470±475. 218 T.T. Kozlowski / Forest Ecology and Management 158 (2002) 195±221 Norby, R.J., Kozlowski, T.T., 1981b. Relative sensitivity of three species of woody plants to SO2 at high or low exposure temperature. Oecologia 51, 33±36. Norby, R.J., Kozlowski, T.T., 1981c. Interactions of SO2 concentration and post-fumigation temperature on growth of woody plants. Environ. Pollut., Ser. A 25, 27±39. Norby, R.J., Kozlowski, T.T., 1982. The role of stomata in sensitivity of Betula papyrifera seedlings to SO2 at different humidities. Oecologia 53, 34±39. Norby, R.J., Kozlowski, T.T., 1983. Flooding and SO2-stress interaction in Betula papyrifera and B. nigra seedlings. For. Sci. 29, 739±750. Norby, R.J., Wullschleger, S.D., Gunderson, C.D., 1996. Tree responses to elevated CO2 and implications for forests. In: Koch, G.W., Mooney, H.A. (Eds.), Carbon Dioxide and Terrestrial Ecosystems. Academic Press, San Diego, CA, USA, pp. 1±21. Nortcliff, S., Ross, S.M., Thornes, J.B., 1990. Soil moisture, runoff and sediment yield from differentially cleared tropical rainforest plots. In: Thomas, J.B. (Ed.), Vegetation and Erosion: Processes and Environment. Wiley, Chichester, UK, pp. 419± 436. Noss, R.F., Cooperrider, A., 1994. Saving Nature's Legacy: Protecting and Restoring Biodiversity. Defenders of Wildlife and Island Press, Washington, DC, USA. Nyman, B., 1961. Effect of red and far-red irradiation on the germination process in seeds of Pinus sylvestris L. Nature 191, 1219±1220. Oberbauer, S.F., Clark, D.B., Clark, D.A., Quesada, M., 1988. Crown light environments of saplings of two species of rain forest emergent trees. Oecologia 75, 207±212. O'Hara, K.L., Vallapil, N.I., 1995. Sapwood-leaf area prediction equations for multi-aged ponderosa pine stands in western Montana and central Oregon. Can. J. For. Res. 25, 1553±1557. O'Hara, K.L., Vallapil, N.I., 1999. MasamÐa ¯exible stand density management model for meeting diverse structural objectives in multi-aged stands. For. Ecol. Manage. 118, 57±71. O'Hara, K.L., Lahde, E., Laiho, O., Norokorp, Y., Saksa, T., 1999. Leaf area and tree increment dynamics on a fertile mixedconifer site in southern Finland. Ann. For. Sci 56, 237±247. Old®eld, M.L., 1995. Biodiversity, values and uses. In: Nierenberg, W.A. (Ed.), Encyclopedia of Environmental Biology, Vol. 1. Academic Press, San Diego, CA, USA, pp. 211±233. Oleksyn, J., Bialobok, S., 1986. Net photosynthesis, dark respiration and susceptibility to air pollution of 20 European provenances of Scots pine Pinus sylvestris L. Environ. Pollut. (Ser. A) 40, 287±302. Oliver, C.D., 1981. Forest development in North America following major disturbances. For. Ecol. Manage. 3, 153±168. Oliver, C.D., Larson, B.C., 1996. Forest Stand Dynamics. Wiley, New York, NY, USA. Olo®nboba, M.O., Kozlowski, T.T., 1982. Effects of three systemic insecticides on seed germination and growth of Pinus halepensis seedlings. Plant and Soil 64, 255±258. Olo®nboba, M.O., Kozlowski, T.T., Marshall, P.E., 1974. Effects of antitranspirants on carbohydrate synthesis, translocation, and incorporation in Pinus resinosa. Plant and Soil 40, 609±617. Olsen, C., 1961. Competition between trees and herbs for nutrient elements in calcareous soil. Symp. Soc. Exp. Biol. 15, 145± 155. Olson, J.S., Steams, F., Nienstaedt, H., 1959. Eastern hemlock seeds and seedings. Response to photoperiod and temperature. Conn. Agric. Exp. Stn., New Haven Bull. 620. Orozco-Segovia, A., Sanchez-Coronado, M.E., Vazquez-Yanes, C., 1993. Light environment and phytochrome controlled germination in Piper auritum. Funct. Ecol. 7, 585±590. Osborne, D.J., 1980. Senescence in seeds. In: Thimann, K.V. (Ed.), Senescence in Plants. CRC Press, Boca Raton, FL, USA, pp. 13±37. Owino, F., 1996. Selection for adaptation in multipurpose trees and shrubs for production and function in agroforestry systems. Euphytica 92, 225±234. Pacala, S.W., Canham, C.D., Silander Jr., J.A., 1993. Forest models de®ned by ®eld measurements. I. The design of a northeastern forest simulator. Can. J. For. Res. 23, 1980±1988. Pacala, S.W., Canham, C.D., Saponara, J., Silander Jr., J.A., Kobe, R.K., Ribbens, E., 1996. Forest models de®ned by ®eld measurements: estimation, error analysis and dynamics. Ecol. Monogr. 66, 1±43. Pearcy, R.W., 1983. The light environment and growth of C3 and C4 species in the understory of a Hawaiian rainforest. Oecologia 58, 26±31. Pearcy, R.W., Osteryoung, K., Calkin, H.W., 1985. Photosynthetic responses to dynamic light environments by Hawaiian trees: time course of CO2 uptake and carbon gain during sun¯ecks. Plant Physiol. 79, 896±902. Pearcy, R.W., Chazdon, R.L., Gross, L.J., Mott, K.A., 1994. Photosynthetic utilization of sun¯ecks: a temporarily patchy resource on a time scale of seconds to minutes. In: Caldwell, M.M., Pearcy, R.W. (Eds.), Exploitation of Environmental Heterogeneity by Plants. Academic Press, San Diego, CA, USA, pp. 175±208. Pereira, J.S., Kozlowski, T.T., 1997. Variations among woody angiosperms in response to ¯ooding. Physiol. Plant. 41, 184± 192. Perry, D.A., 1995. Forests, competition, and succession. In: Nierenberg, W.A. (Ed.), Encyclopedia of Environmental Biology, Vol. 2. Academic Press, San Diego, CA, USA, pp. 135±153. Petersen, T.D., Newton, M., Zedaker, S.M., 1988. In¯uence of Ceanothus velutinus and associated forbs on the water stress and stemwood production of Douglas-®r. For. Sci. 34, 333±343. Peterson, J.K., 1983. Mechanisms involved in delayed germination of Quercus nigra seeds. Ann. Bot. 52, 81±92. Pezeshki, S.R., Chambers, J.L., 1985. Responses of cherrybark oak (Quercus falcata var. pagodaefolia) seedlings to short-term ¯ooding. For. Sci. 31, 760±771. Pimental, D., Stachow, U., Takacs, D.A., Brubaker, H.W., Dumas, A.R., Meaney, J.J., O'Neil, J., Onsi, D.E., Gorzilius, D.B., 1992. Conserving biological diversity in agricultural forestry systems. BioScience 42, 354±362. Pimental, D., Wilson, C., McCullum, C., Huang, R., Dwen, P., Flack, J., Tran, Q., Saltman, T., Cliff, B., 1997. Economic and environmental bene®ts of biodiversity. Nature 47, 747±757. T.T. Kozlowski / Forest Ecology and Management 158 (2002) 195±221 Pin®eld, N.J., Dungey, N.O., 1985. Seed dormancy in Acer: an assessment of the role of the structures covering the embryo. J. Plant Physiol. 120, 65±81. Pin®eld, N.J., Stutchbury, P.A., 1990. Seed dormancy in Acer: the role of testa-imposed and embryo dormancy in Acer velutinum. Ann. Bot. 66, 133±138. Pin®eld, N.J., Stutchbury, P.A., Bazaid, S.A., 1987. Seed dormancy in Acer: is there a common mechanism for all Acer species and what part is played in it by abscisic acid. Plant Physiol. 71, 365±371. Place, I.C.M., 1955. The in¯uence of seed-bed conditions on the regeneration of spruce and ®r. Can. For. Branch Bull. 117. Postel, S., Carpenter, S., 1997. Freshwater ecosystem services. In: Daily, G.C. (Ed.), Nature's Services: Societal Dependence on Natural Ecosystems. Island Press, Washington, DC, USA, pp. 195±214. Potter, C.S., 1999. Terrestrial biomass and the effects of deforestation on the global carbon cycle: results from a model of primary production using satellite observations. BioScience 49, 769±778. Priestley, D.A., 1986. Seed Aging. Cornell University Press, Ithaca, NY, USA. Pukachka, S., Kuiper, P.J.C., 1988. Phospholipid composition and fatty acid peroxidation during ageing of Acer platanoides seeds. Physiol. Plant. 72, 89±93. Purser, M.D., Cundy, T.W., 1992. Changes in soil physical properties due to cable yarding and their hydrologic implications. West. J. Appl. For. 7, 36±39. Pyne, S.J., 1984. Introduction to Wildland Fire Management in the United States. Wiley, New York, NY, USA. Pyne, S.J., Andrews, P.L., Laven, R.D., 1996. Introduction to Wildland Fire. Wiley, New York, NY, USA. Ramakrishnan, P.S., 1995. Shifting cultivation. In: Nierenberg, W.A. (Ed.), Encyclopedia of Environmental Biology, Vol. 3. Academic Press, San Diego, CA, USA, pp. 325±330. Reaka-Kudla, M.L., Wilson, D.E., Wilson, E.O. (Eds.), 1997. Biodiversity. II. Understanding and Protecting our Biological Resources. Joseph Henry Press, Washington, DC, USA. Rediske, J.H., Nicholson, D.C., 1965. Maturation of noble ®r seedÐa biochemical study. Weyerhaeuser For. Pap. 2, 1±15. Reich, P.B., 1983. Effects of low concentrations of ozone on net photosynthesis, dark respiration, and chlorophyll contents on aging hybrid poplar leaves. Plant Physiol. 73, 291±296. Reich, P.B., 1987. Quantifying plant response to ozone: a unifying theory. Tree Physiol. 3, 63±91. Reich, P.B., Amundson, R.G., 1985. Ambient levels of O3 reduce net photosynthesis in tree and crop species. Science 230, 566±570. Reid, D.M., Bradford, K.J., 1984. Effect of ¯ooding on hormone relations. In: Kozlowski, T.T. (Ed.), Flooding and Plant Growth. Academic Press, Orlando, FL, USA, pp. 195±219. Rhoads, C.C., 1996±1997. Single-tree in¯uences on soil properties in agroforestry. Lessons from natural forest and savanna ecosystems. Agrofor. Syst. 35, 71±90. Rice, E.L., 1974. Allelopathy. Academic Press, New York, NY, USA. Rice, E.L., 1984. Allelopathy, 2nd Edition. Academic Press, Orlando, FL, USA. 219 Roberts, B.R., Domir, S.C., 1983. The in¯uence of daminozide and maleic hydrazide on growth and net photosynthesis of silver maple and American sycamore seedlings. Sci. Hortic. 19, 367± 372. Roberts, D.W., 1996a. Modeling forest dynamics with vital attributes and fuzzy systems theory. Ecol. Model. 90, 161±173. Roberts, D.W., 1996b. Landscape vegetation modeling with vital attributes and fuzzy systems theory. Ecol. Model. 90, 175±184. Roden, J.S., Pearcy, R.W., 1993. Effect of leaf ¯utter on the light environment of poplars. Oecologia 93, 201±207. Roe, E.I., 1941. Effect of temperature in seed germination. J. For. 39, 413±414. Rogers, H.H., Prior, S.A., O'Neill, E.G., 1992. Cotton root and rhizosphere responses to free-air CO2 enrichment. Crit. Rev. Plant Sci. 11, 251±263. Rood, S.B., Mahoney, J.M., Reid, D.E., Zilm, L., 1994. Instream ¯ows and the decline of riparian cottonwoods along the St. Mary River. Alberta. Can. J. Bot. 73, 1250±1260. Roos, E.E., 1982. Induced genetic change in seed germplasm during storage. In: Khan, A.A. (Ed.), The Physiology and Biochemistry of Seed Development, Dormancy and Germination. Elsevier, Amsterdam, The Netherlands, pp. 409±434. Rosenberg, D.M., McCully, P., Pringle, C.M., 2000. Global-scale environmental effects of hydrological alterations: introduction. BioScience 50, 746±751. Runkle, J.R., 1985. Disturbance regimes in temperate forests. In: Pickert, S.T.A., White, P.S. (Eds.), The Ecology of Natural Disturbance and Patch Dynamics. Academic Press, New York, NY, USA, pp. 17±33. Sahlen, K., Gjelsvik, S., 1993. Determination of Pinus silvestris seed maturity using leachate conductivity measurements. Can. J. For. Res. 23, 864±870. Salati, E., 1997. The forest and the hydrological cycle. In: Dickinson, R.E. (Ed.), The Geophysiology of Amazonia: Vegetation and Climatic Interactions. Wiley, New York, NY, USA, pp. 273±296. Sanchez, P.A., 1995. Science in agroforestry. Agrofor. Syst. 30, 5± 55. Sasaki, S., 1980a. Storage and germination of some Malaysian legume seeds. Malay. For. 43, 161±165. Sasaki, S., 1980b. Storage and germination of dipterocarp seed. Malay. For. 43, 290±308. Sasaki, S., Kozlowski, T.T., 1966. Variable photosynthetic responses of Pinus resinosa seedlings to herbicides. Nature 209, 1042±1044. Sasaki, S., Kozlowski, T.T., 1968a. The role of cotyledons in early development of pine seedlings. Can. J. Bot. 46, 1173±1183. Sasaki, S., Kozlowski, T.T., 1968b. Effects of herbicides on seed germination and early seedling development of Pinus resinosa. Bot. Gaz. 129, 238±246. Sasaki, S., Kozlowski, T.T., 1968c. Effects of herbicides on respiration of red pine (Pinus resinosa Ait.) seedlings. II. Monuron, diuron, DCPA, Dalapon, CDEC, CDAA, EPTC, and NPA. Bot. Gaz. 129, 286±293. Sasaki, S., Kozlowski, T.T., 1970. Effect of cotyledon and hypocotyl photosynthesis on growth of young pine seedlings. New Phytol. 69, 493±500. 220 T.T. Kozlowski / Forest Ecology and Management 158 (2002) 195±221 Sasaki, S., Kozlowski, T.T., Torrie, J.H., 1968. Effects of pretreatment of pine seeds with herbicides on seed germination and growth of young seedlings. Can. J. Bot. 46, 255±262. Satoo, T., 1966. Variation in response of conifer seed germination to soil moisture conditions. Tokyo Univ. For. Misc. Inf. 16, 17±20. Schier, G.A., Zasada, J.C., 1973. Role of carbohydrate reserves in the development of root suckers in Populus tremuloides. Can. J. For. Res. 3, 243±250. Schopmeyer, C.S. (Ed.), 1974. Seeds of Woody Plants in the United States. Agriculture Handbook 450. US Forest Service, Washington, DC, USA. Schulze, E.-D., Chapin III, F.S., Gebauer, G., 1994. Nitrogen nutrition and isotope differences among life forms at the northern treeline of Alaska. Oecologia 100, 406±412. Scifres, C.J., Brock, J.H., 1969. Moisture-temperature interrelations in germination and early seedling development of mesquite. J. Range Manage. 22, 334±337. Sena Gomes, A.R., Kozlowski, T.T., 1986. The effects of ¯ooding on water relations and growth of Theobroma cacao var. Catongo seedlings. J. Hortic. Sci. 61, 265±276. Sena Gomes, A.R., Kozlowski, T.T., 1988. Physiological and growth responses to ¯ooding of seedlings of Hevea brasiliensis. Biotropica 20, 286±293. Shalhevet, J., Levy, Y., 1990. Citrus trees. In: Stewart, B.A., Nielsen, D.R. (Eds.), Irrigation of Agricultural Crops. Am. Soc. Agron., Madison, WI, USA, pp. 951±986. Shanklin, J., Kozlowski, T.T., 1984. Effect of temperature preconditioning on responses of Fraxinus pennsylvanica seedlings to SO2. Environ. Pollut. (Ser. A) 38, 199±212. Shanklin, J., Kozlowski, T.T., 1985a. Effects of temperature regime on growth and subsequent responses of Sophora japonica seedlings to SO2. Plant and Soil 88, 399±405. Shanklin, J., Kozlowski, T.T., 1985b. Effect of ¯ooding of soil on growth and subsequent responses of Taxodium distichum seedlings to SO2. Environ. Pollut. (Ser. A) 38, 199±212. Shugart, H.H., Smith, T.M., Post, W.M., 1992. The potential for application of individual-based simulation models for assessing the effects of global change. Annu. Rev. Ecol. Syst. 23, 15±35. Skole, D., Tucker, C., 1993. Tropical deforestation and habitat fragmentation in the Amazon: satellite data from 1978 to 1988. Science 260, 1905±1910. Smith, D.M., 1995. Forest stand regeneration: natural and arti®cial. In: Nierenberg, W.A. (Ed.), Encyclopedia of Environmental Biology, Vol. 2. Academic Press, San Diego, CA, USA, pp. 155±165. Smith, D.W., Linnartz, N.E., 1980. The southern hardwood region. In: Barrert, J.W. (Ed.), Regional Silviculture of the United States, 2nd Edition. Wiley, New York, NY, USA, pp. 145±230. Solarova, J., Pospislova, J., Slavik, B., 1981. Gas exchange regulation by changing of epidermal conductance with antitranspirants. Photosynthetica 15, 365±400. Solbrig, O.T., Medina, E., Silva, J., 1996. Biodiversity and Function of Savanna Ecosystems: A Global Perspective. Springer, New York, NY, USA. Solomon, A.M., Bartlein, P.J., 1992. Past and future climate change: response by mixed deciduous±coniferous forest ecosystems in northern Michigan. Can. J. For. Res. 22, 1727±1738. Southwick, S.M., Davenport, T.L., 1986. Characterization of water stress and low temperature effects on ¯ower induction in citrus. Plant Physiol. 81, 26±29. Sparks, R.E., Nelson, J.C., Yin, Y., 1998. Naturalization of the ¯ood regime in regulated rivers: the case of the upper Mississippi River. BioScience 48, 706±720. Speight, M.R., Speechly, H.T., 1982. Pine shoot moth in S.E. Asia. I. Distribution, biology and impact. Commonw. For. Rev. 61, 121±134. Springett, J.A., 1976. The effect of planting Pinus pinaster Ait. on populations of soil microarthropods and on litter decomposition at Gnangara, western Australia. Aust. J. Ecol. 1, 83±87. Spurr, S.H., Barnes, B.V., 1980. Forest Ecology, 3rd Edition. Wiley, New York, NY, USA. Stepniewski, W., Glinski, J., Ball, B.C., 1994. Effects of compaction on soil aeration properties. In: Soane, B.D., van Ouwerkerk, C. (Eds.), Soil Compaction and Crop Production. Elsevier, Amsterdam, The Netherlands, pp. 167±189. Stone, L., Roberts, A., 1991. Conditions for a species to gain advantage from the presence of competitors. Ecology 72, 1964± 1972. Streng, D.R., Glitzenstein, J.S., Harcombe, P.A., 1989. Woody seedling dynamics in an east Texas ¯ood plain forest. Ecol. Monogr. 59, 177±204. Stromberg, C., Tiller, R., Richter, B., 1996. Effects of groundwater on riparian vegetation of semiarid regions, San Pedro, Arizona. Ecol. Appl. 6, 113±131. Sucoff, E., Hong, S.G., 1974. Effect of thinning on needle water potential in red pine. For. Sci. 20, 25±29. Sun Cuiling, Yuwen, G., Quanshu, G., 1997. The changes of nutrient content and its effect on forest growth on the soil degraded by successive crop of Japanese larch. For. Res. 10, 321±326 (in Chinese). Suwannapinunt, W., Kozlowski, T.T., 1980. Effect of SO2 on transpiration, chlorophyll content growth and injury in young seedlings of woody angiosperms. Can. J. For. Res. 10, 78±81. Swaine, M.D., Whitmore, T.C., 1988. On the de®nition of ecological species groups in tropical rain forests. Vegetatio 75, 81±86. Swanson, F.J., Johnson, S.L., Gregory, S.V., Acker, S.A., 1998. Flood disturbance in a forested mountain landscape: interactions of land use and ¯oods. BioScience 48, 681±689. Tang, Z.C., Kozlowski, T.T., 1982a. Physiological, morphological, and growth responses of Platanus occidentalis seedlings to ¯ooding. Plant and Soil 66, 243±255. Tang, Z.C., Kozlowski, T.T., 1982b. Some physiological and growth responses of Betula papyrifera seedlings to ¯ooding. Physiol. Plant. 55, 415±420. Tang, Z.C., Kozlowski, T.T., 1982c. Some physiological and morphological responses of Quercus macrocarpa seedlings to ¯ooding. Can. J. For. Res. 10, 308±311. Tang, Z.C., Kozlowski, T.T., 1983. Responses of Pinus banksiana and P. resinosa seedlings to ¯ooding. Can. J. For. Res. 13, 633± 639. Tappeiner II, J.C., Helms, J.A., 1971. Natural regeneration of Douglas-®r and white ®r on exposed sites in the Sierra Nevada of California. Am. Midl. Nat. 86, 358±370. T.T. Kozlowski / Forest Ecology and Management 158 (2002) 195±221 Taylorson, R.B., Hendricks, S.B., 1976. Aspects of dormancy in vascular plants. BioScience 26, 95±101. Tazaki, T., Ishihara, K., Usijima, T., 1980. In¯uence of water stress on the photosynthesis and productivity of plants in human areas. In: Turner, N.C., Kramer, P.J. (Eds.), Adaptation of Plants to Water and High Temperature Stress. Wiley, New York, NY, USA, pp. 309±321. Tilman, D., 1985. The resource-ratio hypothesis of plant succession. Am. Nat. 125, 827±852. Toole, V.K., Toole, E.H., Hendricks, S.B., Borthwick, H.S., Snow Jr., A.G., 1961. Responses of Pinus virginiana to light. Plant Physiol. 36, 285±290. Torres, F., 1983. Role of woody perennials in animal agroforestry. Agrofor. Syst. 1, 131±163. Toth, L., Martin, S., Arrington, D.A., Chamberlain, J., 1998. Hydrologic manipulations of the channelized Kissimmee River: implications for management. BioScience 48, 757±764. Trapp, E., 1938. Untersuchung uÈber die Verteilung der Helligkeit in einem Buchenstand. Bioklimatologie Ser. B 5, 153±158. Tsukuhara, H., Kozlowski, T.T., 1986. Effects of ¯ooding and temperature regime on growth and stomatal aperture of Betula platyphylla var. japonica seedlings. Plant and Soil 92, 103±112. Tsukahara, H., Kozlowski, T.T., Shanklin, J., 1985. Tolerance of Pinus densi¯ora, Pinus thunbergii, and Larix leptolepis seedings to SO2. Plant and Soil 88, 123±132. Uhl, C., Buschbacher, R., Serrao, E.A.S., 1988. Abandoned pastures in eastern Amazonia. I. Patterns of plant succession. J. Ecol. 76, 663±681. Van den Driessche, R., 1984. Relationships between spacing and nitrogen fertilization of seedlings in the nursery, seedling mineral nutrition, and outplanting performance. Can. J. For. Res. 14, 431±436. Vergara, N.T., Nair, P.K.R., 1983. Agroforestry in the South Paci®c Region Ð an overview. Agrofor. Syst. 3, 363±379. Vertucci, C.W., Leopold, A.C., 1987. Oxidative processes in soybean and pea seeds. Plant Physiol. 84, 1038±1043. Von Carlowitz, F.G., 1985. Some considerations regarding principles and practice of information collection on multipurpose trees. Agrofor. Syst. 3, 181±195. Waisel, Y., Borger, G.H., Kozlowski, T.T., 1969. Effects of phenylmercuric acetate on stomatal movement and transpiration of excised Betula papyrifera leaves. Plant Physiol. 44, 685±690. Wardle, P., 1968. Engelmann spruce (Picea engelmannii Engel.) at its upper limits on the front range. Colorado Ecol. 49, 483±495. Waring, R.H., Running, S.W., 1998. Forest Ecosystems: Analysis at Multiple Scales, 2nd Edition. Academic Press, San Diego, CA, USA. Weaver, H., 1974. Effects of ®re on temperate forests: western United States. In: Kozlowski, T.T., Ahlgren, C.E. (Eds.), Fire and Ecosystems. Academic Press, New York, NY, USA, pp. 279±319. White, C.S., 1986. Effects of prescribed ®re on rates of decomposition and nitrogen mineralization in a ponderosa pine ecosystem. Biol. Fertil. Soils 2, 87±95. White, P.T., 1983. Tropical rain forests: nature's dwindling treasures. Natl. Geogr. 163, 2±47. 221 Whitmore, T.C., 1983. Secondary succession from pine seed in tropical rain forests. For. Abstr. 44, 769±799. Whitmore, T.C., 1989. Canopy gaps and the two major groups of forest trees. Ecology 70, 536±538. Wilgen, B.W., von Siegfried, W.R., 1986. Seed dispersal properties of three pine species as a determinant of invasive potential. S. Afr. J. Bot. 52, 546±548. Willatt, S.T., Pullar, D.M., 1983. Changes in soil physical properties under grazed pastures. Aust. J. Soil Res. 22, 343± 348. Winget, C.H., Kozlowski, T.T., 1965. Yellow birch germination and seedling growth. For. Sci. 11, 386±392. Winget, C.H., Kozlowski, T.T., Kuntz, J.E., 1963. Effects of herbicides on red pine nursery stock. Weeds 11, 87±90. Withgott, J., 1999. Pollen migrates to top of conservation agenda. BioScience 49, 857±862. Wolkowski, R.P., 1990. Relationship between wheel-traf®c induced soil compaction, nutrient availability and crop growth: a review. J. Prod. Agric. 3, 460±469. Wormald, T.L., 1992. Mixed and pure forest plantations in the tropics and subtropics. FAO Forestry Paper no. 103. FAO, Rome, Italy. Wu, C.C., Kozlowski, T.T., 1972. Some histological effects of direct contact of Pinus resinosa seeds and young seedlings with 2,4,5-T. Weed Res. 12, 229±233. Wu, C.C., Kozlowski, T.T., Evert, R.F., Sasaki, S., 1971. Effects of direct contact on Pinus resinosa seeds and young seedlings with 2,4-D or picloram on seedling development. Can. J. Bot. 49, 1737±1742. Yamamoto, F., Kozlowski, T.T., 1987a. Effect of ¯ooding tilting of stems, and ethrel application on growth, stem anatomy, and ethylene production of Pinus densi¯ora seedlings. J. Exptl. Bot. 38, 293±310. Yamamoto, F., Kozlowski, T.T., 1987b. Effect of ¯ooding of soil on growth, stem anatomy, and ethylene production of Cryptomeria japonica seedlings. Scand. J. For. Res. 2, 45±58. Yarie, J., Viereck, L., Van Cleve, K., Adams, P., 1998. Flooding and ecosystem dynamics along the Tanana River. BioScience 48, 690±695. Zackrisson, O., Nilsson, M.C., 1992. Allelopathic effects by Empetrum hermaphroditum on seed germination of two boreal tree species. Can. J. For. Res. 22, 1310±1319. Zavitkovski, J., Newton, M., 1968. Ecological importance of snowbrush, Ceanothus velutinus, in the Oregon Cascades agricultural ecology. Ecology 49, 1134±1145. Zekri, M., 1993. Salinity and calcium effects on emergence, growth and mineral composition of seedlings of eight citrus rootstocks. J. Hortic. Sci. 68, 53±62. Zhang, J., Davies, W.J., 1990. Changes in the concentration of ABA in xylem sap as a function of changing soil water status can account for changes in leaf conductance and growth. Plant Cell Environ. 13, 277±286. Zobel, B.J., Talbert, J., 1984. Applied Forest Tree Improvement. Wiley, New York, NY, USA. Zobel, B.J., van Wyck, G., Stahl, P., 1987. Growing Exotic Forests. Wiley, New York, NY, USA.