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Transcript
Forest ecology Introduction Forest ecology is a part of ecology that is concerned with forests as opposed to grasslands, savannas, or tundra. Ecology is the study of the processes of interaction among organisms and between organisms and their environment. Ecology is often subdivided into physiological ecology, population ecology, community ecology, and ecosystem ecology. Forest ecology has generally focused on forest trees so it could provide the ecological basis for silviculture, forest management, and forest economics. Forestry has always had an interest in the ecology of trees but in the first half of the last century, forest ecology was mostly included within silviculture [1]. Silviculture originally used an agricultural model, viewing forest trees as a perennial crop. Starting in the 1960s, forestry began to consider forests not just as stands of trees but as ecosystems (see Ecosystem) and to be interested in the many other services that ecosystems supply [2]. In the past decades, forest ecology increasingly became forest ecosystem ecology. Forest ecology has profited from interaction with several other disciplines, particularly hydrology, meteorology, soil science, geomorphology, economics, and wildlife management. These disciplines not only brought an enlarged understanding of the physical environment and its coupling to forest ecology but also brought new conceptual tools, for example, sediment budgets, dissolved chemicals, water budgets, and heat budgets. In turn, forest ecology has interested the geosciences and economics in ecosystems. This synergy could lead to a better understanding of ecosystem processes and economic processes through ecosystem services [3]. Forest ecology’s approach to study was influenced by agriculture’s clinical approach of using field trials and correlational studies. Only in the last few decades has a more process approach (“how things work”) begun (see Process models). A process approach has allowed forest ecology to more easily extend its methodologies beyond case studies and statistical models based on specific data sets (e.g., Ref. 4). Trees live a long time and, as a result, the establishment of permanent plots with periodic remeasurement has been a significant part of forestry data collection as far back as the 1700s. The alternatives to these longitudinal studies are comparative studies and chronosequences. Comparative studies use measurements of morphology and environmental conditions to establish their statistical relationships and to infer the functional importance of morphology, physiology, and interspecific variation. This approach has important limitations in determining and understanding functional mechanisms (see e.g., Ref. 5). Chronosequence studies use plots of different ages to represent the same plot being traced through time. The assumption is that each plot, although different in age, has traced exactly the same history up to their present age. Although this approach is widely practiced, the assumptions underlying this method are rarely tested, and when they have been, they have often proved to be invalid (see e.g., Ref. 6). Introductions to forest ecology can be found in Refs 7–10. The different contents of these texts indicate the varying interests of forest ecology. The rest of this article briefly considers some parts of forest ecology that have developed approaches which have been particularly fruitful in recent decades. Watersheds and Water Budgets Forest Services in North America, starting mainly in the 1950s, set up experimental watersheds in most different forest types. The water, biogeochemical, and sediment budgets approach used in watershed research resulted in a more process-oriented view of forest ecosystems; this approach allowed a practical means of organizing and integrating the various flows of water, chemicals, sediment, heat energy, and biomass productivity. Hubbard Brook in New Hampshire, United States was one of the earliest to profit from this expanded viewpoint. Early in the 1960s, studies at Hubbard Brook [11] noted the increase in ions of H, SO4 , and NO2 in wet and dry precipitation. This “acid precipitation” had been recognized earlier in northern Europe as being due to industrial sources but its effects and biophysical processes were not yet well understood. Because of the interest in small watershed hydrology (i.e., connections between hillslopes and first-order streams – (see Catchment hydrology)), biogeochemistry (i.e., Encyclopedia of Environmetrics, Online © 2006 John Wiley & Sons, Ltd. This article is © 2013 John Wiley & Sons, Ltd. This article was published in Encyclopedia of Environmetrics Second Edition in 2012 by John Wiley & Sons, Ltd. DOI: 10.1002/9780470057339.vnn137 2 Forest ecology not just nutrient ions), and vegetation ecology (particularly productivity and plant composition), the Hubbard Brook studies [12] were interested in following the acid precipitation through the canopy into the forest floor and into the streams. These studies and others [13, 14] discovered that the tree canopies acted as exchange surfaces to modify the wet and dry precipitation as it passed through to the forest floor. The Hubbard Brook studies also explained how increases in mobile anions of strong acids of sulfur and nitrogen increased transport (leaching) through the soil profile and into first-order streams and how these effects were neutralized by the third- and fourth-order streams [15, 16]. Leaching is the chemical process of exchange of cations between a stationary anion (organic matter and clay) and mobile anions in the weak electrolyte soil solution. Hubbard Brook also pioneered watershed manipulations to study the effects of both experimental and forestry practices on forest populations and biogeochemistry. One of these experiments, the killing of all plants for two years to exaggerate the biogeochemical response to this unnatural disturbance, proved useful in understanding the role of the nitrogen cycle in the recovery from natural and anthropogenic disturbances [17, 18]. Andrews Forest in Oregon is perhaps the bestknown research watershed to the general public because of its contribution to the spotted owl and oldgrowth issues [19]. Its scientific contribution to forest ecology included studies on old-growth forests, large woody debris, and eco-hydrology [20]. Study of oldgrowth in the Andrews Forest also led to recognition of the importance of large woody debris on carbon dynamics in both uplands and streams [21, 22]. In streams, the supply of large tree trunks was crucial in structuring stream habitat for aquatic organisms, particularly salmon [23]. Forest Geomorphology Landscapes are made up of ridgelines, peaks, saddles, and stream courses or hollows (convergent areas without streams); between these are hung hillslopes. Hillslopes are conveyor belts for downslope movement of sediments and chemicals in solution. Thus, any section of the hillslope consists of two inputs and one output. The soil (if not transported by glaciation) is created by weathering from the bedrock, that is, soil production. Soil above the bedrock is moved into and out of a hillslope section as a function of slope angle, soil type, moisture content, and burrowing organisms [24]. These forces create hillslopes of certain shapes which in turn affect the downslope hydrology and thus create the moisture gradient from dry at the top of hillslopes to wet at the bottom. These hydrological processes also carry dissolved chemical ions, particularly nutrients such as nitrogen, calcium, magnesium, and phosphorus [25, 26]. Many studies have shown the importance of hillslope geomorphological and hydrological processes and an increasing number of studies have shown the importance of organisms in creating hillslope processes, for example, tree uprooting, burrowing, and soil organisms. The transfer of water, biogeochemicals, and sediments from uplands (hillslopes) to streams creates soil moisture–nutrient gradients that are significant in the plant distributions within watersheds [27, 28]. These moisture–nutrient gradients are the result of hydrologic and geomorphic processes on the hillslope. Hillslope shape and elevation are the result of the transfer of sediments and dissolved chemicals downslope and to first-order streams. This in turn defines how and where streams will form and how dissected the watershed will be. Since hillslopes are the terrain in which forest ecology is most interested, this dissection (the amount and steepness) of the uplands is essential to understanding the physical template on which forest ecosystems reside. Ecosystem Management Ecosystem management calls attention to the fact that forests must be managed for more than the trees [29]. One significant idea that ecosystem management introduced was the role of natural disturbance. By viewing natural disturbances as a recurrent part of ecosystems, a new model for managing forests developed, namely, that forestry could try to mimic natural disturbances. This was a major departure from the agricultural/silvicultural model and incorporated the idea that cutting trees in a forest was a kind of disturbance. Mimicking disturbance has to this point been largely a regime approach in which descriptors Encyclopedia of Environmetrics, Online © 2006 John Wiley & Sons, Ltd. This article is © 2013 John Wiley & Sons, Ltd. This article was published in Encyclopedia of Environmetrics Second Edition in 2012 by John Wiley & Sons, Ltd. DOI: 10.1002/9780470057339.vnn137 Forest ecology such as disturbance type, occurrence, distribution, size, seasonality, severity, and intensity are thought of as a multivariate space in which forest management should attempt to occupy a similar hyperspace as natural disturbances for a specific ecosystem. A good description of this approach for the boreal forest of eastern Canada can be found in Ref. 30. The regime approach is still a classification/topological approach and does not necessarily lead to an understanding of how the disturbance produces a specific ecological effect. However, despite ecosystem management’s present limitations in understanding of ecosystem processes, it is a major step forward in forest ecology and management. References [1] Puettmann, K.J., Coates, D., & Messier, C. (2009). A Critique of Silviculture: Managing for Complexity, Island Press, Washington. [2] Christensen, N.L., Bartuska, A., Brown, J.H., Carpenter, S., D’Antonio, C., Francis, R., Franklin, J.F., MacMahon, J.A., Noss, R.F., Parsons, D.J., Peterson, C.H., Turner, M.G., & Woodmansee, R.G. (1996). The scientific basis for ecosystem management, Ecological Applications 6, 665–691. [3] Costanza, R., d’Arge, R., de Groot, R., Farber, S., Grasso, S., Hannon, B., Limburg, K., Naeem, S., O’Neill, R.V., Paruelo, V., Raskin, R.G., Sutton, P., & van den Belt, M. (1997). The value of the world’s ecosystem services and natural capital, Nature 387, 253–260. [4] Maurer, B.A. (1999). Untangling Ecological Complexity, University of Chicago Press, Chicago. [5] Ackerly, D.D. (1999). Comparative plant ecology and the role of phylogenetic information, in Physiological Plant Ecology, M.C. Press, J.D. Scholes, & M.G. Barker, eds, Blackwell Science, Oxford, pp. 391–413. [6] Johnson, E.A. & Miyanishi, K. (2008). Testing the assumptions of chronosequences in succession, Ecology Letters 11, 419–431. [7] Barnes, B.V., Zak, D.R., Denton, S.R., & Spurr, S.H. (1998). Forest Ecology, 4th Edition, John Wiley & Sons, Inc., New York. [8] Kimmins, J.P. (2004). Forest Ecology: A Foundation for Sustainable Forest Management and Environmental Ethics in Forestry, 3rd Edition, Prentice-Hall, Upper Saddle River. [9] Oliver, C.D. & Larson, B.C. (1990). Forest Stand Dynamics, McGraw-Hill Inc., New York. [10] Waring, R.H. & Running, S.W. (2007). Forest Ecosystems: Analysis at Multiple Scales, 3rd Edition, Elsevier, Amsterdam. 3 [11] Likens, G.E., Bormann, F.H., Pierce, R.S., Eaton, J.S., & Johnson, N.M. (1977). Biogeochemistry of a Forested Ecosystem, Springer-Verlag, New York. [12] Likens, G.E., Driscoll, C.T., & Buso, D.C. (1996). Longterm effects of acid rain: response and recovery of a forested ecosystem, Science 272, 244–246. [13] Lindberg, S.E., Lovett, G.M., Richter, D.D., & Johnson, D.W. (1986). Atmospheric deposition and canopy interactions of major ions in a forest, Science 231, 141–145. [14] Lovett, G.M. & Lindberg, S.E. (1993). Atmospheric deposition and canopy interactions of nitrogen in forests, Canadian Journal of Forest Research 23, 1603–1616. [15] Johnson, N. (1979). Acid rain: neutralization within Hubbard Brook ecosystem, Science 204, 497–499. [16] Hedin, L.O., Likens, G.E., Postek, K.M., & Driscoll, C.T. (1990). A field experiment to test whether organic acids buffer acid deposition, Nature 345, 798–800. [17] Likens, G.E., Bormann, F.H., Johnson, N.M., Fisher, D.W., & Pierce, R.S. (1970). Effects of forest cutting and herbicide treatment on nutrient budgets in the Hubbard Brook watershed ecosystem, Ecological Monographs 40, 23–47. [18] Vitousek, P.M., Gosz, J.R., Grier, C.C., Melillo, J.M., Reiners, W.A., & Todd, R.L. (1979). Science 204, 469–474. [19] T.A., Spies & S.L. Duncan, eds (2009). Old Growth in a New World: A Pacific Northwest Icon Reexamined , Island Press, Washington. [20] Swanson, F.J. & Jones, J.A. (2001). Geomorphology and Hydrology of the H. J. Andrews Experimental Forest, Blue River, Oregon. Modular Field Guide to the H. J. Andrews. [21] Spies, T.A., Franklin, J.F., & Thomas, T.B. (1988). Coarse woody debris in Douglas-fir forests of Western Oregon and Washington, Ecology 69, 1689–1702. [22] Laudenslayer, W.F., Shea, P.J., Valentine, B.E., Weatherspoon, C.P., Lisle, T.E., & Technical Coordinators. (2002). Proceedings of the Symposium on the Ecology and Management of Dead Wood in Western Forests. 2–4 November 1999; Reno, NV. (Gen. Tech. Rep. PSWGTR-181. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture), pp. 949. [23] Montgomery, D.R. (2003). King of Fish: The ThousandYear Run of Salmon, Westview Press, Boulder. [24] Anderson, R.S. & Anderson, S.P. (2010). Geomorphology: The Mechanics and Chemistry of Landscapes, Cambridge University Press, Cambridge. [25] Yoo, K., Amundsen, R., Heimsath, A.M., & Dietrich, W.E. (2006). Spatial patterns of soil organic carbon on hillslopes: Integrating geomorphic processes and the biological C cycle, Geoderma 130, 47–65. [26] Yoo, K., Amundsen, R., Heimsath, A.M., Dietrich, W.E., & Brimhall, G.H. (2007). Integration of geochemical mass balance with sediment transport to calculate rates of soil chemical weathering and transport on hillslopes, Journal of Geophysical Research 112, F02013. Encyclopedia of Environmetrics, Online © 2006 John Wiley & Sons, Ltd. This article is © 2013 John Wiley & Sons, Ltd. This article was published in Encyclopedia of Environmetrics Second Edition in 2012 by John Wiley & Sons, Ltd. DOI: 10.1002/9780470057339.vnn137 4 Forest ecology [27] Bridge, S.R.J. & Johnson, E.A. (2000). Geomorphic principles of terrain organization and vegetation gradients, Journal of Vegetation Science 11, 57–70. [28] Chipman, S.J. & Johnson, E.A. (2002). Understory vascular plant species diversity in the mixed wood boreal forest of Western Canada, Ecological Applications 12, 588–601. [29] F.B. Samson & F.L. Knopf, eds (1996). Ecosystem Management: Selected Readings, Springer, New York. [30] S., Gauthier, M.A. Vaillancourt, A. Leduc, L. De. Grandpré, D. Kneeshaw, H. Morin, P. Drapeau, & Y. Bergeron, eds (2009). Ecosystem Management in the Boreal Forest, Presses de l‘Université du Québec, Québec. (See also Agroforestry; Ecosystem monitoring; Forest growth and yield modeling; Forest health monitoring; Forest inventory; Forestry; Tree morphology) Encyclopedia of Environmetrics, Online © 2006 John Wiley & Sons, Ltd. This article is © 2013 John Wiley & Sons, Ltd. This article was published in Encyclopedia of Environmetrics Second Edition in 2012 by John Wiley & Sons, Ltd. DOI: 10.1002/9780470057339.vnn137 E. A. JOHNSON