Environmental Engineering Reference
In-Depth Information
readily available, use of such spatially extensive data has become commonplace in ecol-
ogy, with a broadening of the ecosystem perspective to extend beyond the narrow focus
carried over from the system science of the mid-twentieth century.
Before we outline a way of thinking about heterogeneity and ecosystems, we give some
examples of ecosystem heterogeneity. Recall that the ecosystem concept requires that the
boundaries be set by the researcher, so different ecosystems can have very different con-
tent and spatial extent (see Chapters 1 and 9). This explains why we can give such diverse
examples of heterogeneity within and outside of particular ecosystems.
Boreal Forest Fire Mosaics
Boreal forests cover wide expanses, and many retain aspects of the natural regimes of
disturbance that have shaped them for centuries. One of the first such areas to be well
documented was the 400,000-ha Boundary Waters Canoe Area in Minnesota. Myron
Heinselman (1973)
documented the pattern of burned areas over the landscape by examin-
ing scars on the trunks of trees that survived the catastrophic fires. The kinds of mosaics
he documented have now become familiar through many studies elsewhere (
Figure 10.4
;
Turner and Romme 1994
). It is clear that spatial heterogeneity, expressed as the pattern of
Large Fire
Perimeters
Towns/Villages
Railroads
YEAR
1950-1959
Roads
1960-1969
1970-1979
1980-1989
1990-1999
2000-2005
Primary
Secondary
Ignition Locations
Natural Cause
Human Cause
Note: Ignition Locations displays
point locations of fire's directly
affecting Denali National Park
and Preserve
National Park Services
Alaska Support Office
FIle Management Program
1:1,000,000
N
W
E
S
0 5
10
20
30
40
Miles
FIGURE 10.4
A fire mosaic in coniferous forest in the Denali National Park and Reserve, and adjacent areas
of Alaska from 1950 through 2000. Ages of stands postfire are shown in decadal classes. In addition, whether a
fire was set by people or ignited by natural forces is indicated.
(Image in the public domain.)
