Ecosystem Ecology:

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

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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)

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Simple ecosystem model

• Key Attributes
• Biotic and abiotic processes
• Pools and fluxes

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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)

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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.)

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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
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Spatial scale
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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

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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.

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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

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General Approaches

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

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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?

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Ecosystem components

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

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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 CO2 increases
  temperature, increasing respiration,
  increasing CO2 
• 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

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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 CO2 to organic matter, and
  thereby providing the energy feeding the entire
  system
• Respiration another key ecosystem process
  oxidizes organic matter to CO2, consuming the
  energy provided by photosynthesis, and thereby
  returns CO2 to the atmosphere
• Other examples of ecosystem processes
  Weathering, Evaporation, Nutrient uptake, Death
  decomposition, Herbivory

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Controls over ecosystem processes state factors,
interactive controls, and feedbacks
State factors set the boundaryconditions
theyare independent of ecosystem processes
These effects (between interactive controls and
ecosystem processes) are mediated by feedbacks
Interactive controls bothaffect and
areaffected by ecosystem processes
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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)

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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)
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History of Ecosystem Ecology contributions from
various disciplines

• Vasily Vasilyevich Dokuchaiev (1846-1903)
• 1880s, 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)

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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 Dokuchaievs 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

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History of Ecosystem Ecology contributions from
various disciplines

• Raymond L. Lindeman (1915-1942), American
  limnologist, The trophic-dynamic 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

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History of Ecosystem Ecology contributions from
various disciplines

• Lindemans model system at Cedar Bog Lake in
  Minnesota

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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 Lindemans, but for
  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

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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
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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

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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.