Environmental Engineering Reference
In-Depth Information
Vegetation Pattern
A complex aspect of design, vegetation pattern is commonly a process of self-sorting by the spe-
cies selected. Common factors that should be considered initially include vegetation zonation,
mosaic/cluster, edge, slope and aspect (i.e., orientation), soil affinity, and moisture requirements
or tolerance. Some general factors exist to help guide some of the decisions, but not entirely. The
collection of reference site data should reflect the distribution and pattern on the land of the key
species. Vegetation data should provide guidance on how the individual plants are arranged on the
land, information that can be applied to the design of a restoration project. The planting layout
must consider slope and solar aspect to ensure that sun-tolerant species are placed in appropriately
sunny and warm areas and that species which require cooler and moister conditions are placed
on slopes less exposed to the sun. Likewise, species that are less tolerant to extreme sun and heat
should not be placed on west- and south-facing slopes.
ZONATION
Zonation is a common vegetation pattern of bands or other shapes that are frequently influenced
by elevation, moisture, soils, or the effects of plant competition and that may occur either over a
large geographic area or in small areas. Zonation is easily observed in wetland situations from the
water surface to the tops of riverbanks and higher elevations. This pattern is observable in small
prairie patches, vernal pools, or seasonal wetlands with an elevation change of as little as six inch-
es. Upland species also exhibit a zonation pattern, although it is not always as easily detected as
in wetlands. This pattern commonly occurs on hillsides in drainages, canyons, and ravines. The
vegetation may be responding to gradients in climate, moisture, elevation, slope exposure (north
versus south facing), or other environmental factors.
MOSAIC/CLUSTER
A mosaic/cluster pattern can be found in many vegetation communities. The sources for this
pattern are many. Soil types, compaction of soil, availability of moisture, seed distribution, seed
viability, timing of rainfall, resistance of seed to periods of drought, predation on seed, and her-
bivore preference in grazing are some factors contributing to species sorting in the vegetation.
Urbanization has also contributed to this mosaic pattern with the introduction of exotic landscap-
ing that contrasts dramatically with the adjacent wildlands. These urban landscapes have divided
up the vegetation into small, isolated colonies of native vegetation, causing fragmentation of the
resources and creating less optimum habitat for native species.
EDGE
In some vegetation communities and regions of the world, the important aspect of the site, to wildlife,
is either the amount of edge to area between contrasting vegetation types (ecotone) or the extent of
homogeneous vegetation. Figure 6-5 illustrates three examples of configuration in a mosaic or cluster
situation. The edge in figure 6-5a is significantly higher than that in figure 6-5c even though there is
the same amount of vegetation area for the two areas illustrated. This situation may be important for
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