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Explanations of buttress formation: (reviewed by Hartshorn 1983) 1. Adaptive responses to wind or gravity stresses. 2. Negative geotropism. 3. Conduction shortcut. 4. Mechanical stimulation of strains caused by winds. Christensen-Dalsgaard, K. K., A. R. Ennos, and M. Fournier. 2008. Are radial changes in vascular anatomy mechanically induced or an ageing process? Evidence from observations on buttressed tree root systems. Trees-Structure and Function 22:543-550. Clair, B., M. Fournier, M. F. Prevost, J. Beauchene, and S. Bardet. 2003. Biomechanics of buttressed trees: Bending strains and stresses. American Journal of Botany 90:1349-1356. Mattheck, C., W. Albrecht, F. Dietrich, and R. Kriechbaum. 1994. The Biomechanics of Rays in Trees. Allgemeine Forst und Jagdzeitung 165:143147. Tang, Y., X. F. Yang, M. Cao, C. C. Baskin, and J. M. Baskin. 2011. Buttress trees elevate soil heterogeneity and regulate seedling diversity in a tropical rainforest. Plant and Soil 338:301-309. Young, T. P., and V. Perkocha. 1994. Treefalls, Crown Asymmetry, and Buttresses. Journal of Ecology 82:319-324. Elmqvist et al. 1994. Effects of Tropical Cyclones Ofa and Val on the Structure of a Samoan Lowland Rain Forest. Biotropica 26: 384-391. The frequency of uprooted trees was 31 percent after Ofa, but only 16 percent after Val. Uprooting was significantly more frequent among species lacking buttresses or stilt roots. The results of our study support the windresistance hypothesis. However, in studies following hurricane Hugo in Puerto Rico, no clear difference in wind resistance between trees with different morphology was found. STILT ROOTS: •adventitious roots •common in mangroves •common in palms Avalos, G., and M. F. Otarola. 2010. Allometry and Stilt Root Structure of the Neotropical Palm Euterpe Precatoria (Arecaceae) Across Sites and Successional Stages. American Journal of Botany 97:388-394. Goldsmith, G. R., and R. A. Zahawi. 2007. The function of stilt roots in the growth strategy of Socratea exorrhiza (Arecaceae) at two neotropical sites. Revista de Biologia Tropical 55:787-793. Greig, N., and J. D. Mauseth. 1991. Structure and Function of Dimorphic Prop Roots in Piper-Auritum l. Bulletin of the Torrey Botanical Club 118:176-183. Hanagata, N., T. Takemura, I. Karube, and Z. Dubinsky. 1999. Salt water relationships in mangroves. Israel Journal of Plant Sciences 47:63-76. TROPICAL LEAVES RAINFOREST LEAVES: •usually mesophyll •20-182 cm2 upper surf. area •oval and unlobed •smooth margins •long-lived •drip tips are common Drip tips speed water runoff and drying of the leaf surface (Dean and Smith 1978). BakerBrosh, K. F., and R. K. Peet. 1997. The ecological significance of lobed and toothed leaves in temperate forest trees. Ecology 78:1250-1255. Burd, M. 2007. Adaptive function of drip tips: a test of the epiphyll hypothesis in Psychotria marginata and Faramea occidentalis (Rubiaceae). Journal of Tropical Ecology 23:449455. Ivey, C. T., and N. DeSilva. 2001. A test of the function of drip tips. Biotropica 33:188-191. Lucking, R., and A. Bernecker-Lucking. 2005. Drip-tips do not impair the development of epiphyllous rain-forest lichen communities. Journal of Tropical Ecology 21:171-177. VARIATION IN TROPICAL LEAVES: •compound leaves more common in lowlands •leaf size declines with average temperature of coolest month •leaves are smaller on poorer soils Leigh 1999 EPIPHYTES: •attach firmly to other plants •trap soil particles for nutrients •create unique ecosystems •moist conditions are necessary •most common in pre- and lower montane rainforests •arboreal mammals may prevent extreme epiphyte abundance on upper branches •families include: Bromeliaceae, Orchidaceae (1200 spp. In CR) and Araceae •abundance and species richness is more pronounced in Neotropics EPIPHYLLS: •tiny epiphytes occurring on leaf surfaces •include mosses, liverworts, lichens, and algae •common in understory of lowland wet life zones •usually detrimental •drip tips enhance runoff, reducing epiphyll loads •canopy lichens fix nitrogen Dyer and Letourneau 2006. Determinants of Lichen Diversity in a Rain Forest Understory. BIOTROPICA 39(4): 525–529 2007. Epiphyll cover (mosses, liverworts, and lichens) was greater on plants that had ant-mutualists and balanced resources. Lichen species richness was greater for plants with balanced resources, particularly for those with high light availability. In this system, natural sources of variation were reliable determinants of lichen diversity and both biotic and abiotic influences were important. VINES: Climbers: vines (herbaceous) and lianas (woody) Bignoniaceae the most common family Lianas are more common in drier forests Thick lianas indicate undisturbed forest (Hartshorn 1983) Stranglers: Ficus (Moraceae) and Clusia (Guttiferae) Start out as epiphytes, send down woody, clasping roots Kill tree with dense monolayer of evergreen leaves on top Tropical Rainforest Constants Leaf area index (LAI): LAI = L/A, where L = upper leaf area, A = area of the forest (no dimensions). Traditionally calculated via measuring the leaf area above a square meter of forest floor, so that LAI = L, the total leaf area (without dimensions). BCI LAI = 8 Temperate forest LAI = 6 Tropical Rainforest constants: •LAI is 7-8 •trees drop 6-8 tons dry wgt lvs/ha/yr •death rates of trees >= 10cm dbh = 1-2%/yr •basal area (total cross sectional area at 1.3 m above ground of all trees >= 10cm dbh) near 30m2/ha and above-ground biomass near 300 tons dry wgt/ha Bala ant Paraponera clavata La Selva: 18 4.5 per hectare Protect .04 tons wet-weight leaves per hectare per year. DISCUSSION OF LEIGH 2009 What are the roles of phenotypic plasticity versus fixed adaptations in generating Leigh’s forest constants? What controls forest productivity? What governs forest structure? How do animals shape the botanical characteristics of tropical forests? Why are there so many species of tropical trees? How has math helped answer these questions? STRUCTURE OF A “RAINFOREST” I. Structural complexity II. Telling the trees from the forest A. Buttresses and prop roots B. Trunks and crowns C. Leaves D. Variation across life zones III. Vines and epiphytes IV. Flowers, fruits and seeds V. Diversity revisited VI. GAPS HIGHER GROUND ADAPTING TO LIFE IN THE FOREST CANOPY EPIPHYTE DIVERSITY • Over 20,000 species in total • 10% of all vascular plants • More than 80 families contain epiphytes – Monocots are dominant group in epiphytes – Ferns are roughly 1/3 number of epiphytes – Gymnosperms very rare: • Seeds not dispersed easily • Wind pollination inefficient for epiphytes MAJOR FAMILIES • POLYPODIACEAE (ferns): most of 1100 • ORCHIDACEAE (monocots): 13,000/19,000 • ARACEAE (monocots): 1350/2500 • BROMELIACEAE (monocots): 1144/2500 • PIPERACEAE (dicots): 710/3100 • MELASTOMATACEAE (dicots): 648/4770 EVOLUTIONARY HISTORY • POLYPHYLETIC (in unrelated groups) • RECENT development (Pliocene/Pleistocene) – WHY? Animal dispersers evolved during late Tertiary and early Quaternary – EVIDENCE: Current high rates of genetic evolution in certain groups; – Highest diversity in geologically young MONTANE habitats GLOBAL RANGE • Epiphytes are found in virtually all humid tropical forests; • Highest diversity in pre-montane and montane forests with high air moisture • Drier forests have lower diversity but may have equal densities of stress-tolerant epiphytes, as well as abundant vines and lianas WINTER • FROST: Primary limiting factor in latitudinal ranges • Hardy epiphytes: Tillandsia usneoides, Polypodium polypodioides (along SE coast) • Mistletoe: Parasite protected by host body • Nonvascular epiphytes: temperate rainforests have large bryophyte and lichen populations NONVASCULAR EPIPHYTES • What is a LICHEN? – SYMBIOSIS between a fungus and photosynthetic algae (or cyanobacteria) • Dessication Strategy – POIKILOHYDRY – Nitrogen Fixation: Decreases Water Need • EPIPHYLLS – Most primitive form of epiphytism How to classify Arboreal Flora? • POLYPHYLETIC • No Unifying Characteristics • Several Different Systems: – – – – – Relation with Host Growth Habit Light Humidity Substrate DEFINITIONS • VINE: herbaceous climber with soil contact • LIANA: woody climber with constant soil contact • HEMIEPIPHYTES: – PRIMARY: Germinate as epiphyte, form soil contact – SECONDARY: Germinate in soil, climb into canopy • HOLOEPHIPHYTES: True Epiphytes BENEFITS for Epiphytes • Higher levels of sunlight • Lower levels of competition for light resources • Lower amounts of herbivory (especially from large mammals) • Lower investment in support structure Partitioning Light Resources Epiphytic Bromeliads • Evolved from terrestrial ancestor from arid habitat (well-suited for epiphytism) • 3 Different Basic Forms – Tank Bromeliads – Atmospheric Bromeliads – Ant-House Bromeliads TANK BROMELIADS Tank Bromeliad Fauna INTERACTIONS WITH HOST • COMMENSALISM? 1. Epiphyte Load 2. Nutritional Piracy a. Throughfall interception b. Canopy roots 3. Parasitism Ant-Plant Interactions • Myrmecochory • Pollination (quite rare) • Leaf-cutter ants Myrmecophily • Ant-mediated protection • Myrmecotrophy Myrmecophytic Strategies Protection-based • Plants are defended against herbivory and competition • Ants may receive shelter and specialized food bodies or extrafloral nectar Nutrition-based • Plants obtain nutrients from ants through stems or root systems • Ants receive nesting sites or nest structural support, as well as food bodies or nectar Epiphytes as Myrmecotrophs • Epiphytes have greater requirements for both water and nutrients • Epiphytes experience less herbivory and competition over light resources than terrestrial species • Many arboreal ant species are well-suited for myrmecotroph association • Myrmecotrophs tend to colonize exposed, nutrient-poor areas where the ant-plant mutualism provides necessary advantages Ant-Garden vs. Ant-House Myrmecotrophs • Ant-garden epiphytes obtain nutrients from arboreal carton nests in which ants plant their seeds • These plants offer food bodies and nectar, as well as support and drainage (through transpiration) of the arboreal nests • Ant-house epiphytes absorb nutrients through stems or adventitious roots from inhabitant ants • These epiphytes provide nesting sites within their vegetative structures, and offer limited rewards to the ants Ant-House Bromeliads Transition from tank morphology to anthouse myrmecotroph Bromeliad trichomes facilitated ant-house adaptations Bulbous waterproof chambers formed by leaf morphology Ant-House Orchids Hollow pseudobulbs with natural entrance holes Solutes absorbed by adventitious roots inside pseudobulbs Extrafloral nectaries may attract larger ants that defend the orchid more successfully Ant-House Ferns Ant-House Rubiaceae Chamber Morphology Ant colonies use the dry, smooth-walled cavities for their brood, and store debris and prey items in the “warted” chambers, where the plant can absorb nutrients directly from organic debris. YANAYACU • Premontane wet tropical forest • Highest diversity of epiphyte groups • Lower diversity of vines and lianas LA SELVA • High diversity of all groups of arboreal flora (Epiphyte diversity higher in premontane wet forest) BARRO COLORADO ISLAND • Fairly rich flora of epiphytes and arboreal fauna • Not as diverse in arboreal flora as tropical wet forest (La Selva) or premontane wet forest (Yanayacu) ACG • Shares under 5% of epiphyte community with La Selva • Relatively low diversity (High local densities of vines and lianas) SERENGETI • Orchids and vines only in riverine forest habitat (seasonal rains and humid shade) MILNE BAY • Mangrove forests often contain halophytic plants including hardy epiphytes, lichens, and parasitic plants FLOWERS: •flowering time is variable •mass flowering can be common •pollination syndromes and coevolution are common •large, showy bracts are common •asexual reproduction may be more important for some species •is self compatability more common in rainforests? Sequential blooming and synchronous fruiting in 6 species of Shorea. FRUITS AND SEEDS: •fruit size and structure variable •very large fruits are common •seed dispersal is variable (wind 31% at ACG, 8% at La Selva) (La Selva 50% bird dispersed, 13% bats) •seed predation is high Gross Primary Productivity: The total amount of solar radiation converted by plants into chemical energy (i.e. sugars) Net Primary productivity: Amount of carbon fixed in excess of the respiratory needs of the plant. Most biological metabolic activity takes place within the range 0-50o C. The optimal temperatures for productivity are 15-25o C. The productivity of plants, especially at the local scale, can also be controlled by the availability of nutrients. “Nutrients are regenerated more rapidly in tropical than in temperate forests.” Ultisols: well-weathered, acidic soils (nutrient-poor) Inceptisols: young soils of recent origin, rich in minerals near the surface, higher pH (but still acidic) RESOURCE AVAILABILITY HYPOTHESIS: plant species adapted to resource-limited habitats have inherently slower relative growth rates, contain higher levels of carbon based defenses, and are less preferred by herbivores (Janzen 1974, Coley et al. 1985). WITHIN A HABITAT: In resource-limited habitats within-species allocation of nutrients to growth has highest priority, and allocation to defenses increases when resource-limiting conditions improve (Bazzaz et al. 1987). (predicts that at higher relative growth rates, concentrations of defensive compounds will be greater than at lower rgr) Carbon/nutrient balance hypothesis: A plant’s C:N ratio determines its nutritive quality and palatability to generalist herbivores and is an adaptive response to herbivory that evolved under constraints of availability of resources in the environment (Bryant et al. 1983). predicts lower herbivory in nutrient stressed plants (high C:N), and high rates in fertilized plants (low C:N) PLANT STRESS HYPOTHESIS Insect herbivores preferentially attack stressed plants because of breakdown and mobilization of nitrogen-containing compounds (White 1974). Predicts outbreaks and increased herbivory on nutrient stressed plants PLANT VIGOR HYPOTHESIS (concentrates on specialist, rather than generalist herbivores): Vigorously growing plants are more favorable to specialist herbivores (Price 1991) Feller, I.C. 1995. Effects of nutrient enrichment on growth and herbivory of dwarf red mangrove (Rhizophora mangle). Ecological Monographs 65:477-505. Is nutrient limitation responsible for the slow growth and characteristic physiognomy of dwarf red mangrove trees in the interior of a mangrove island? How does increased nutrient availability affect herbivory in red mangrove?