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 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
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
–
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…
• 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)
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 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
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.