Environmental Engineering Reference
In-Depth Information
Boundary Effects
Boundaries between systems that are structurally or compositionally different are impor-
tant aspects of heterogeneity (
Cadenasso et al. 2004
). Boundaries may act as barriers, may
serve as distinctive habitat zones, or be areas of dynamic interaction between patches. For
example, the wall of vegetation that exists between forests and open fields is an important
boundary for wind, aerosols, and certain animals (
Figure 10.8
;
Weathers et al. 2001
). The
movement of nutrients and organisms between the forest and field can be controlled by the
structure of those boundaries. As a result of the physical environmental patterns and resource
gradients, boundaries are likely to be locations of great contrast in ecosystem functions.
Boundaries rarely exist in landscapes and ecosystems in isolation. Indeed, different
boundaries may interact. However, the interaction of multiple boundaries has rarely been
investigated.
Porensky (2011)
provides a compelling example, based on research on aban-
doned livestock corrals in East Africa (
Figure 10.9
). Such patches can last for decades or
centuries, and are nutrient-rich, treeless glades that influence the distribution of plants
and animals. The areas between glades differed depending on whether other glades were
less than 150 m away, or more than 250 m distant. Areas between close glades had double
the number of trees, half the use by large herbivores, and less cover of open-site grasses.
Even the ant species associated with
Acacia
trees differed between close and distant glades.
Such a complex of differences may have many implications for ecosystem processes.
Management and Built Patches
Few contemporary ecosystems lack signs of the activities of humans, and many are
dominated by human activities and artifacts (
Vitousek et al. 1997
). Human activities and
3.0
Edge
Interior
Open field
2.5
2.0
1.5
1.0
0.5
0.0
FIGURE 10.8
Input of atmospheric nutrients and pollutants at a forest-field edge; DIN
5
dissolved inorganic
nitrogen. Bulk water input in the open field represents the ambient nutrient flux from the atmosphere to the ter-
restrial ecosystem. Intact forest edge experiences higher inputs of sulfate, nitrate, and ammonium than do the for-
est interior or the open field.
(Data from
Weathers et al. 2001
.)
