An Overview of Ecosystems and Ecosystem Characteristics
1. Components of ecosystems
a) structure: the physical configuration of the system:
These are "the parts" and consist of the amounts and
composition of the biotic and abiotic components.
b) processes: the flow of energy, the cycling of materials.
Examine figure 1.4 c (pg 12)...key diagram...models of carbon
(energy), nutrients, water, and the minimum amount of complexity
needed to study these three.
We've been doing this for the net radiation balance:
ecosystem model: As we saw, the presence and type of biota can
influence reflectance (albedo) and the partitioning of remaining
energy into H and LE. That partitioning, in turn, affects the
local temperature which then determines the amount of longwave
radiation.
Without "knowing what's inside the box (i.e., the composition of
the ecosystem)", it's still possible to describe ecosystem
characteristics in terms of energy flow, water budgets, etc., and
this type of information composed the content of early ecosystem
studies.
CHARACTERISTICS OF ECOSYSTEMS
Author points out that both Productivity and soil types appear to
be largely determined by inputs:
ordination of systems by temp and moisture. Temp, moisture and the
biotic structure of ecosystems are not independent variables.
Biota affect both physical variables to some degree...
A robust description of ecosystems comes from Hans Jenny,
particularly his 1980 book, The Soil Resource.
Ecosystem as function of
1. climate,
2. organisms,
3. parent material, (the geological material that contributes to
soil formation)
4. topography. (slope and aspect), and
5. time since formation, i.e., since the last catastrophic
disturbance,
Jenny makes argument that, even though strong interactions between
these variables exist now....Historically or over geological time
scale...variable orthogonal. Plate tectonics determines shape,
location of land masses, solar radiation is a constant, organisms
move around...evolved under condition of constraints potentially
unrelated to present climate.
Parent material may describe potential fertility of soils, slope
and aspect impose rules of gravity flow that dictate movement of
materials, and time since origin of system determine strengths of
various interactions (e.g. have the biota changed the soil...has
the climate changed the soil, etc).
NOTE THAT WE USED THE JENNY FORMULA IN MY DEFINITION OF THE
COMPLEXITY OF ECOLOGY...THE SPATIALLY EXPLICIT INTERACTION OF
ORGANISMS UNDER A DEFINED SET OF CLIMATIC, EDAPHIC AND DISTURBANCE
REGIME.
If you know climate variables alone, it is possible to predict the
potential structure and processing rates of system, but not actual
system...
If this course was offered 2 billion years ago...we could have a
very simple model...
Ecosystem studies would be simple if all we had to deal with was
green slime and a few heterotrophic microbes...
Did you ever play a game with someone who kept changing the rules?
Biota do this, via creation of new biochemical pathways...how one
type of vegetation...a coniferous forest, a grassland, etc.
responds to precip and temp will be different from another
system...Man is trying to do get more directly involved in this
game via bioengineering.
PREDICTING STRUCTURE AND PROCESSING BY CLIMATE, ALONE
(ordination of biomes)
POTENTIAL EVAPOTRANSPIRATION (please know this term!) (PET) is the
mm of H20 that could be evaporated if water was not limiting. This
sounds like a clean definition...but somewhat complicated.
Vegetation with lots of leaf area, under adequate water conditions,
can evaporate more water than a smooth surface of water (say, from
a pan). Moreover, smaller pans can evaporate more water per unit
area than larger pans..due to the concept of boundary
layers. The data we have from energy budget, Rn = (1-a)S-L = H +
LE, as H goes to 0, all net radiation can be converted to
evaporating water, hence PET (mm H2O) approaches Rn/calories needed
to evaporate 1 mm H20. In practice PET never equals Rn, only
approaches the value.
ACTUAL EVAPOTRANSPIRATION (AET) = (an empirically measured) amount
of water evaporated at a site, function of both how much solar
energy is present and whether or not water available to evaporate.
In desert, have lotsa radiation but no water; hence, no AET. In
arctic, lotsa water, but very litter radiation; hence, we again
have a low AET.
Figure 2.2, ecosystem types in relation to precip and temperature
values:
Ecosystem type AET PET AET/PET dominant soil name
Tundra 150 300 0.5 Histosol
Boreal Forest 300 450 0.67 Spodosol/Entisol
Temp. Grassland 300 420 0.71 Mollisol
Temp decid For. 690 700 0.99 Alfisol
Temp shrublands 300 400 0.75 Aridisol
Temp. coniferous 550 600 0.92 Spodosol
Temp rain forest 700 700 1.00 Spodosol
Tropical grassland 400 800 0.50 Mollisol
Tropical shrub 400 800 0.50 Aridisol
Trop. season. for.1000 1400 0.71 Ultisol
Trop. rain for. 1600 1600 1.00 Oxisol
RETURN TO HOME PAGE