Site Analysis - Project Planning and Management for Ecological Restoration - page 58

target species. In many cases, the site will be adjacent to existing vegetation and the combination
of the two areas will be sufficient. Knowing the target species' habitat requirements is important in
determining what will be needed.
BIOLOGICAL FACTORS
The level of investigations varies with the anticipated changes being proposed and the presence
of existing resources that may either be negatively affected or serve as a source for design develop-
ment. Describing the various attributes of the biotic environment and the individual key species
will be important in understanding how the site is being used by those resources.
Existing Vegetation Communities. Taking note of existing native vegetation on-site begins the
process of compiling a species list and identifying the communities to be restored. Healthy stands
of desirable species can be preserved and enhanced and can serve as sources for seeds, cuttings, and
transplanting. Equally important is the identification of noxious, invasive weeds and other undesir-
able species that may require removal or ongoing management. Decisions on the composition of
plant species will strongly influence the ultimate design and management of the project site.
Some sites may have been totally cleared or manipulated, resulting in a complete loss of native
vegetation. Information on the vegetation that once occupied the site will require observing adja-
cent lands or going further off-site. In some cases, records, diaries, and journals from early settlers,
biologists, and museum collections can also be used to reconstruct the vegetation community.
Vegetation Dynamics. Regardless of the past degradation of a site, vegetation undergoes con-
stant changes in response to environmental stimuli, such as rain, erosion, soil conditions, and the
season. Another variable is the natural competition among plant species.
Vegetation communities undergo a maturation process, with more and more biomass being
developed as well as a constant change in microenvironments. Microenvironments may include
the canopy of taller plants or the leaf litter depth, indicating a long-term presence of some types
of vegetation. Natural processes, such as floods and fire, as well as migrating grazing animals con-
tribute to the physical appearance of the vegetation. If one or more of these naturally occurring
processes is absent, then it is likely that the vegetation community will not be on the same track
as vegetation in locations with those processes. For example, heath in Great Britain represents
an intermediate succession stage and requires active management for its continued existence.
Continual human-caused fires suppressed the establishment of pines that normally would have
eventually occupied the landscape.
The same situation is found for several endangered species where the vegetation is no longer
being subjected to natural disruptive occurrences. In the western United States, the endangered
least Bell's vireo occurs in an intermediate-growth form of willow riparian habitat. Periodic flood-
ing of the rivers restores or returns stretches of the river habitat back to early riparian stages. The
vireo can relocate to take advantage of these locations as they develop to a stature the vireo finds
suitable. Loss of flooding by controlling floodwater with dams has been a significant factor in the
loss of succession diversity on rivers in the western United States. Another example is the endan-
gered Stephen's kangaroo rat, which occurs in semiopen scrubland habitat that used to be kept
open by browsing deer and antelope, now largely absent from the rat's range. The senior author