ECOREGION
)
a
Climate
Disturbance
Soil
Time
Type
Ecotype
Hy
y
ph
d
ro
ra phy)
log
og ra
p g
y
To hysio
P
(
)
b
100,000
Physiography
10,000
Geomorphology
Soil Texture
Geomorphic Unit
Slope Position
Hydrology
1000
Water Level Permafrost
Soil Moisture
Regional
100
Vegetation
Climate
Disturbance
Fire
Structure
Fluvial
Plant Association
Thermokarst
Human
100
1
1
10
100
1000
10,000
100,000
1,000,000
Space (m2)
Figure 1. Interaction of interrelated state factors that control structure and
function of ecosystems.
Oberbauer et al. 1989). Vegetation typically is the
larger scale components, such as climate or physi-
most important factor controlling the trophic
ography (Fig. 1b). The climate factor, particularly
structure of ecosystems because it controls pri-
temperature and precipitation, globally accounts
mary productivity, and affects material and
for the largest amount of variation in ecosystem
energy exchange, provides structure and energy
structure and function globally (Walter 1979,
for other trophic levels, and affects soil erosion
Vitousek 1994, Bailey 1998). Physiography, or
and geomorphic processes (Walter 1979, Bailey
broad-scale landforms, with a characteristic geo-
1996). For biotic classification, vegetation has the
logic substrate, surface shape, and relief, are the
advantage over faunal components in that plants
boundary conditions that control the spatial
are relatively immobile and thus easier to charac-
arrangement and rate of geomorphic processes.
terize and map (Brown et al. 1998). Natural and
Thus physiography affects the material (charac-
human disturbances have long been recognized
teristic lithologies or soil texture) and energy
as important factors affecting the timing and
flows that affect ecosystem development (Wah-
development of ecosystems (Watt 1947, Forman
rhaftig 1965, Swanson et al. 1988, Bailey 1996). Soil
1995). Because the consequences and mechanisms
moisture and hydrologic movement are critical
of disturbance are different at various hierarchi-
factors in the water balance of plants and the
cal levels (Pickett et al. 1989), and thus very com-
availability of nutrients (Fitter and Hay 1987,
2
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