Ecosystem Ecology Case studies on the Colorado Plateau

Ecosystem Ecology: Case studies on the Colorado Plateau FOR 479 FOR 599 BIO 479 BIO 599 Stephen C. Hart Self-proclaimed “Ecosystem Ecologist” School of Forestry, NAU

What is an Ecosystem? • A bounded ecological system consisting of all the organisms in an area and the physical environment with which they interact (Chapin et al. 2002) • The sum of all of the biological and non-biological parts of an area that interact to cause plants to grow and decay, soil or sediments to form, and the chemistry of water to change (Aber & Melillo 2001)

What is an Ecosystem? • A community and its environment treated together as a functional system of complementary relationships, and transfer and circulation of energy and matter (Whittaker 1975) • Any unit that includes all of the organisms (i. e. , “the community”) in a given area interacting with the physical environment so that the flow of energy leads to clearly defined trophic structure, biotic diversity, and material cycles (i. e. , exchange of materials between living and nonliving parts) within the system (E. Odum 1971)

Simple ecosystem model Key Attributes: • Biotic and abiotic processes • Pools and fluxes

What is Ecosystem Ecology? • the study of the interactions among organisms and their environment as an integrated system (Chapin et al. 2002) • the study of the movement of energy and materials, including water, chemicals, nutrients, and pollutants, into, out of, and within ecosystems (Aber & Melillo 2001)

Ecosystem Structure & Function • Ecosystem Structure – The vertical and horizontal distribution of ecosystem components (e. g. , vegetation ht. , distribution of plant biomass above and below ground, etc. ) • Ecosystem Function – processes that are conducted or evaluated at the ecosystem scale (e. g. , NPP, nutrient uptake, actual evapotranspiration, etc. )

Interdisciplinary 1) ecosystem processes are controlled by factors traditionally in the purview of separate disciplines, and 2) questions in ecosystem ecology cross broad scales in space and time The unique contribution of ecosystem ecology is its focus on biotic and abiotic factors as interacting components of a single integrated system

Spatial scale

Delineating Ecosystem Boundaries • How do we decide where to draw the lines around an ecosystem? • Depends on the scale of the question being asked – Small scale: e. g. , soil core; appropriate for studying microbial interactions with the soil environment, microbial nutrient transformations – Stand: an area of sufficient homogeneity with regard to vegetation, soils, topography, microclimate, and past disturbance history to be treated as a single unit; appropriate questions include impact of forest management on nutrient cycling, effects of acid deposition on forest growth

Delineating Ecosystem Boundaries Natural Boundaries: ecosystems sometimes are bounded by naturally delineated borders (lawn, crop field, lake); appropriate questions include whole-lake trophic dynamics and energy fluxes (e. g. , Lindeman 1942) Watershed: a stream and all the terrestrial surface that drains into it • rich history of watershed scale studies in ecosystem ecology (“Small Watershed Approach” e. g. Bormann and Likens 1967) • watershed studies use streams as ‘sampling device’, recording surface exports of water, nutrients, carbon, pollutants, etc. , from the watershed; deforestation impacts on water supply to a city.

Time Scales in Ecosystem Ecology • Instantaneous: leaf-level photosynthesis and sunflecks • Seasonal: deciduous forest, desert grassland • Successional: 3 months after fire, 300 years after fire • Species migration/invasions: 1 to thousands of years • Evolutionary history: Archaea and methane production • Geologic history: glacial/interglacial cycles

General Approaches • Systems approach – Top-down – Based on observations of general patterns • Mechanistic approach – Bottom-up – Based on process understanding

Levels of Simplifying Assumptions • Equilibrium - many early studies assumed some ecosystems were at equilibrium with their environment – – Closed systems dominated by internal recycling of materials Self-regulation and deterministic dynamics Stable endpoints or cycles Absence of disturbance and human influence • Steady State – Balance between inputs and outputs to the system show no temporal trend (allows for spatial and temporal variation) • Dynamic change – directional changes caused by humans?

Ecosystem components • • Plants Decomposers Animals Abiotic components – Water – Atmosphere – Soil minerals

Feedbacks • Negative feedbacks ( homeostatic) – when two components of a system have opposite effects on each other – i. predator – prey – ii. thermostat • Positive feedbacks – when two components of a system have the same effect (positive or negative) on each other – runaway greenhouse effect – rising CO 2 increases temperature, increasing respiration, increasing CO 2 • Negative feedbacks are key to maintaining ecosystems in a given state, because they resist change • Positive feedbacks, if unchecked, have the potential to shift ecosystems from one state to another

Ecosystem processes: transfers of energy and materials from one pool to another • Can be transfers within the ecosystem, or, transfers between the ecosystem and its surroundings (e. g. , atmosphere) – Photosynthesis is a key ecosystem process, converting atmospheric CO 2 to organic matter, and thereby providing the energy feeding the entire system – Respiration – another key ecosystem process; oxidizes organic matter to CO 2, consuming the energy provided by photosynthesis, and thereby returns CO 2 to the atmosphere – Other examples of ecosystem processes: Weathering, Evaporation, Nutrient uptake, Death & decomposition, Herbivory

Controls over ecosystem processes: state factors, interactive controls, and feedbacks State factors set the boundary conditions – they are independent of ecosystem processes These effects (between interactive controls and ecosystem processes) are mediated by feedbacks Interactive controls both affect and are affected by ecosystem processes

Why should we care about Ecosystem Ecology? • Ecosystem ecology provides a mechanistic basis for understanding the Earth System • Ecosystems provide goods and services to society • Human activities are changing ecosystems (and therefore the Earth System)

History of Ecosystem Ecology: contributions from various disciplines… • • • Tansley, British plant ecologist (1935) “The use and abuse of vegetational concepts and terms, ” Ecology First to coin term, ‘ecosystem’; emphasized interactions between biotic and abiotic; argued against exclusive focus on organisms “The more fundamental conception is. . . the whole system, including not only the organism complex, but also the whole complex of physical factors forming what we call the environment. . . the habitat factors in the widest sense. . Our natural human prejudices force us to consider the organisms. . . as the most important parts of these systems, but certainly the inorganic ‘factors’ are also parts, . . . and there is constant interchange of the most various kinds within each system, not only between the organisms but between the organic and inorganic. These ecosystems, as we may call them, are of the most various kinds and sizes. ” Frederick Frost Blackman (1866 -1947), Plant physiologist (left) Sir Arthur George Tansley (1866 -1947), Plant ecologist (right)

History of Ecosystem Ecology: contributions from various disciplines… • Vasilyevich Dokuchaiev (1846 -1903) • 1880 s, led Russian soil scientists in developing a new scientific philosophy about soils and their relationship to climate, vegetation, parent material and time • Dokuchaiev demonstrated that the most prevalent soils in any region of Russia, when broadly classified in terms of their most prominent soil profile characteristics, correlated well with climatic zones (zonal soils; intrazonal – influenced more by other factors and azonal - undeveloped)

History of Ecosystem Ecology: contributions from various disciplines… • Hans Jenny (1899 -1992), soil scientist, “Factors of Soil Formation” (1941), and “The soil resource: origin and behavior” (1980) • Formalized quantitatively Dokuchaiev’s factors of soil formation (S = f(clorpt)) • Many patterns of soil and ecosystem properties correlate with state factors - for example, very good correlation on the global scale between climate and ecosystem structure and processes

History of Ecosystem Ecology: contributions from various disciplines… • Raymond L. Lindeman (1915 -1942), American limnologist, “The trophicdynamic aspects of ecology” (1942) in journal Ecology • Quantified pools and fluxes of energy in a lake ecosystem, emphasizing biotic and abiotic components and exchanges • Fluxes of energy, critical ‘currency’ in ecosystem ecology, basis for comparison among ecosystems • Synthesized with mathematical model • Coupled energy flow with nutrient cycling

History of Ecosystem Ecology: contributions from various disciplines… • Lindeman’s model system at Cedar Bog Lake in Minnesota

History of Ecosystem Ecology: contributions from various disciplines… • J. D. Ovington, English forester (1962) • Central question, how much water and nutrients are needed to produce a given amount of wood? • Constructed ecosystem budgets of nutrients, water, and biomass (like Lindeman’s, but forests) • Also included inputs and outputs: exports of logs involves exports of nutrients, thus inputs of nutrients to forest required to maintain productivity • One of the first to state the need for more basic understanding of ecosystem function for managing natural resources

History of Ecosystem Ecology: contributions from various disciplines… • Used radioactive tracers to study movement of energy and materials through a coral reef, documenting patterns of whole system metabolism Eugene P. Odum, 1913 -2002 • Systems analysis Howard T. Odum, 1924 -2002

Earth System and Global Change – Making History in Ecosystem Ecology • Impact of human activities on Earth has led to the need to understand how ecosystem processes affect the atmosphere and oceans • Large spatial scale, requiring new tools in Ecosystem Ecology – Eddy flux tower measurements of gas exchange over large regions – Remote sensing from satellites – Global networks of atmospheric sampling – Global models of ecosystem metabolism

Earth System and Global Change – Making History in Ecosystem Ecology Frontiers in Ecosystem Ecology, integrating systems analysis, process understanding, and global scale – How do changes in the environment alter the controls over ecosystem processes? – What are the integrated system consequences of these changes? – How do these changes in ecosystem properties influence the earth system? Rapid human-induced changes occurring in ecosystems have blurred any previous distinction between basic research and management application.