Ecosystem ecology is the integrated study of living (biotic) and non-living (abiotic) components of ecosystems and their interactions within an ecosystem framework. This science examines how ecosystems work and relates this to their components such as chemicals, bedrock, soil, plants, and animals. Ecosystem ecologists study these relationships on large scales, linking biological diversity with ecosystem sustainability and function.
Ecosystem ecology examines physical and biological structures and examines how these ecosystem characteristics interact with each other. Ultimately, this helps us understand how to maintain high quality water and economically viable commodity production. A major focus of ecosystem ecology is on functional processes, ecological mechanisms that maintain the structure and services produced by ecosystems. These include primary productivity (production of biomass), decomposition, and trophic interactions.
Studies of ecosystem function have greatly improved human understanding of sustainable production of forage, fiber, fuel, and provision of water. Functional processes are mediated by regional-to-local level climate, disturbance, and management. Thus ecosystem ecology provides a powerful framework for identifying ecological mechanisms that interact with global environmental problems, especially global warming and degradation of surface water.
This example demonstrates several important aspects of ecosystems: Ecosystem boundaries are often nebulous and may fluctuate in time Organisms within ecosystems are dependent on ecosystem level biological and physical processes Adjacent ecosystems closely interact and often are interdependent for maintenance of community structure and functional processes that maintain productivity and biodiversity
These characteristics also introduce practical problems into natural resource management. Who will manage which ecosystem? Will timber cutting in the forest degrade recreational fishing in the stream? These questions are difficult for land managers to address while the boundary between ecosystems remains unclear; even though decisions in one ecosystem will affect the other. We need better understanding of the interactions and interdependencies of these ecosystems and the processes that maintain them before we can begin to address these questions.
Ecosystem ecology is an inherently interdisciplinary field of study. An individual ecosystem is composed of populations of organisms, interacting within communities, and contributing to the cycling of nutrients and the flow of energy. The ecosystem is the principal unit of study in ecosystem ecology.
Population, community, and physiological ecology provide many of the underlying biological mechanisms influencing ecosystems and the processes they maintain. Flowing of energy and cycling of matter at the ecosystem level are often examined in ecosystem ecology, but, as a whole, this science is defined more by subject matter than by scale. Ecosystem ecology approaches organisms and abiotic pools of energy and nutrients as an integrated system which distinguishes it from associated sciences such as biogeochemistry.Chapman, S.K., Hart, S.C., Cobb, N.S., Whitham, T.G., and Koch, G.W. (2003). "Insect herbivory increases litter quality and decomposition: an extension of the acceleration hypothesis". in: Ecology 84:2867-2876.
Biogeochemistry and hydrology focus on several fundamental ecosystem processes such as biologically mediated chemical cycling of nutrients and physical-biological cycling of water. Ecosystem ecology forms the mechanistic basis for regional or global processes encompassed by landscape-to-regional hydrology, global biogeochemistry, and earth system science.
History Ecosystem ecology is philosophically and historically rooted in terrestrial ecology. The ecosystem concept has evolved rapidly during the last 100 years with important ideas developed by Frederic Clements, a botanist who argued for specific definitions of ecosystems and that physiological processes were responsible for their development and persistence.Hagen, J.B. (1992). An Entangled Bank: The origins of ecosystem ecology. Rutgers University Press, New Brunswick, N.J. Although most of Clements ecosystem definitions have been greatly revised, initially by Henry Gleason and Arthur Tansley, and later by contemporary ecologists, the idea that physiological processes are fundamental to ecosystem structure and function remains central to ecology.
Later work by Eugene Odum and Howard T. Odum quantified flows of energy and matter at the ecosystem level, thus documenting the general ideas proposed by Clements and his contemporary Charles Elton.
In this model, energy flows through the whole system were dependent on biotic and abiotic interactions of each individual component (species, inorganic pools of nutrients, etc.). Later work demonstrated that these interactions and flows applied to nutrient cycles, changed over the course of succession, and held powerful controls over ecosystem productivity.Odum, E.P 1969. "The strategy of ecosystem development". in: Science 164:262-270.Likens, G. E., F. H. Bormann, N. M. Johnson, D. W. Fisher and R. S. Pierce. (1970). "Effects of forest cutting and herbicide treatment on nutrient budgets in the Hubbard Brook watershed-ecosystem". in: Ecological Monographs 40:23-47. Transfers of energy and nutrients are innate to ecological systems regardless of whether they are aquatic or terrestrial. Thus, ecosystem ecology has emerged from important biological studies of plants, animals, terrestrial, aquatic, and marine ecosystems.
Ecosystem services
Ecosystem services are ecologically mediated functional processes essential to sustaining healthy human societies.Chapin, F.S. III, B.H., Walker, R.J., Hobbs, D.U., Hooper, J.H., Lawton, O.E., Sala, and D., Tilman. (1997). "Biotic control over the functioning of ecosystems". in: Science 277:500-504. Water provision and filtration, production of biomass in forestry, agriculture, and fisheries, and removal of greenhouse gases such as carbon dioxide (CO2) from the atmosphere are examples of ecosystem services essential to public health and economic opportunity. Nutrient cycling is a process fundamental to agricultural and forest production.
However, like most ecosystem processes, nutrient cycling is not an ecosystem characteristic which can be "dialed" to the most desirable level. Maximizing production in degraded systems is an overly simplistic solution to the complex problems of hunger and economic security. For instance, intensive fertilizer use in the midwestern United States has resulted in degraded fisheries in the Gulf of Mexico.Defries, R.S., J.A. Foley, and G.P. Asner. (2004). "Land-use choices: balancing human needs and ecosystem function". in: Frontiers in ecology and environmental science. 2:249-257. Regrettably, a "Green Revolution" of intensive chemical fertilization has been recommended for agriculture in developed and developing countries.Chrispeels, M.J. and Sadava, D. (1977). Plants, food, and people. W. H. Freeman and Company, San Francisco.Quinones, M.A., N.E. Borlaug, C.R. Dowswell. (1997). "A fertilizer-based green revolution for Africa". In: Replenishing soil fertility in Africa. Soil Science Society of America special publication number 51. Soil Science Society of America, Madison, WI. These strategies risk alteration of ecosystem processes that may be difficult to restore, especially when applied at broad scales without adequate assessment of impacts. Ecosystem processes may take many years to recover from significant disturbance.
For instance, large-scale forest clearance in the northeastern United States during the 18th and 19th centuries has altered soil texture, dominant vegetation, and nutrient cycling in ways that impact forest productivity in the present day.Foster, D. R. (1992). "Land-use history (1730-1990) and vegetation dynamics in central New England, USA". In: Journal of Ecology 80: 753-772.Motzkin, G., D. R. Foster, A. Allen, J. Harrod, and R. D. Boone. (1996). "Controlling site to evaluate history: vegetation patterns of a New England sand plain". In: Ecological Monographs 66: 345-365. An appreciation of the importance of ecosystem function in maintenance of productivity, whether in agriculture or forestry, is needed in conjunction with plans for restoration of essential processes. Improved knowledge of ecosystem function will help to achieve long-term sustainability and stability in the poorest parts of the world.
Operation Biomass productivity is one of the most apparent and economically important ecosystem functions. Biomass accumulation begins at the cellular level via photosynthesis. Photosynthesis requires water and consequently global patterns of annual biomass production are correlated with annual precipitation.Huxman TE, ea.(2004). "Convergence across biomes to a common rain-use efficiency". Nature. 429: 651-654 Amounts of productivity are also dependent on the overall capacity of plants to capture sunlight which is directly correlated with plant leaf area and N content.
Net primary productivity (NPP) is the primary measure of biomass accumulation within an ecosystem. Net primary productivity can be calculated by a simple formula where the total amount of productivity is adjusted for total productivity losses through maintenance of biological processes:
NPP = GPP – Rproducer
Where GPP is gross primary productivity and Rproducer is photosynthate (Carbon) lost via cellular respiration.
NPP is difficult to measure but a new technique known as eddy co-variance has shed light on how natural ecosystems influence the atmosphere. Figure 4 shows seasonal and annual changes in CO2 concentration measured at Mauna Loa, Hawaii from 1987 to 1990. CO2 concentration steadily increased, but within-year variation has been greater than the annual increase since measurements began in 1957.
These variations were thought to be due to seasonal uptake of CO2 during summer months. A newly developed technique for assessing ecosystem NPP has confirmed seasonal variation are driven by seasonal changes in CO2 uptake by vegetation.Goulden, M. L., J. W. Munger, S.-M. Fan, B. C. Daube, and S. C. Wofsy, (1996). "Effects of interannual climate variability on the carbon dioxide exchange of a temperate deciduous forest". In: Science 271:1576-1578Barford, C. C., ea. (2001). "Factors controlling long and short term sequestration of atmospheric CO2 in a mid-latitude forest". In: Science 294: 1688-1691 This has led many scientists and policy makers to speculate that ecosystems can be managed to ameliorate problems with global warming. This type of management may include reforesting or altering forest harvest schedules for many parts of the world.
Decomposition and nutrient cycling Decomposition and nutrient cycling are fundamental to ecosystem biomass production. Most natural ecosystems are nitrogen (N) limited and biomass production is closely correlated with N turnover.Vitousek, P.M. and Howarth, R.W. (1991). "Nitrogen limitation on land and in the sea: how can it occur?" In: Biogeochemistry 13:87-115.Reich, P.B., Grigal, D.F., Aber, J.D., Gower, S.T. (1997). "Nitrogen mineralization and productivity in 50 hardwood and conifer stands on diverse soils". In: Ecology 78:335-347.