Basic Concepts and Management Issues of Rivers - River Dynamics and Integrated River Management - page 24

at some points and deposition at others. Thus, woody debris accumulation can influence pool distribution,
and the formation of microhabitats for aquatic communities.
The sensitivity of animal communities to vegetative characteristics is well recognized. Numzerous
animal species are associated with particular plant communities, many require particular developmental
stages of those communities (e.g., old-growth,) and some depend on particular habitat elements within
those communities (e.g., snags). The structure of streamside plant communities also directly affects aquatic
organisms by providing inputs of appropriate organic materials to the aquatic environment and providing
cover along banks, and by influencing instream habitat structure through inputs of woody debris (Gregory
et al. 1991).
Plant communities can be viewed in terms of their internal complexity, including the number of layers
of vegetation and the species comprising each layer; competitive interactions among species; and the
presence of detrital components, such as litter, downed wood, and snags. Species and age composition of
vegetation structure also can be extremely important. The quality and vigor of the vegetation can affect
the productivity of fruits, seeds, shoots, foots, and other vegetative features. Poorer vigor can result in
less food and fewer consumers (wildlife).
Plant communities are dynamic and change over time. The differing regeneration strategies of particular
vegetation types lead to characteristic patterns of plant succession following disturbances in which
pioneer species well-adapted to bare soil and plentiful light are gradually replaced by longer-lived species
that can regenerate under more shaded and protected conditions.
Terrestrial fauna —Stream corridors are used by wildlife more than any other habitat type (Thomas et
al. 1979) and are a major source of water to wildlife populations. The faunal composition of a stream
corridor is a function of the interaction of food, water, cover, and spatial arrangement (Thomas et al.
1979). Stream corridors offer the optimal habitat for many forms of wildlife because of the proximity to a
water source and an ecological community that consists primarily of hardwoods in many parts of the
U.S., which provide a source of food, such as nectar, catkins, buds, fruit, and seeds (Harris 1984).
The spatial distribution of vegetation is also a critical factor for wildlife. The linear arrangement of streams
results in a maximized edge effect that increases species richness because a species can simultaneously
access more than one cover (or habitat) type and exploit the resources of both (Leopold 1933). Edges occur
along multiple habitat types including the aquatic, riparian, and upland habitats. Forested connectors
between habitats establish continuity between forested uplands that may be surrounded by unforested
areas. These act as feeder lines for dispersal and facilitate repopulation by plants and animals. Thus,
connectivity is very important for retaining biodiversity and genetic integrity on a landscape basis.
Reptiles and amphibians —Nearly all amphibians (salamanders, toads, and frogs) depend on aquatic
habitats for reproduction and overwintering. While less restricted by the presence of water, many reptiles
are found primarily in stream corridors and riparian habitats. Thirty-six of the 63 reptile and amphibian
species found in west-central Arizona in the U.S. were found to use riparian zones. In the Great basin, 11
of 22 reptile species require or prefer riparian zones (Ohmart and Anderson, 1986).
Birds —Birds are the most commonly observed terrestrial wildlife in riparian corridors. Bird species
richness reflects the vegetative diversity and width of the river corridor. Over half of these breeding birds
are species that forage for insects on foliage (e.g. vireos, warblers) or species that forage for seeds on the
ground (e.g. doves, orioles, grosbeaks, and sparrows). Next in abundance are insectivorous species that
forage on the ground or on trees (e.g. thrushes, and woodpeckers).
Mammals —The combination of cover, water, and food resources in riparian areas makes them desirable
habitat for large mammals such as deer, moose, and elk that can use multiple habitat types. Other mammals
depend on riparian areas in some or all of their range.
Hoover and Wills (1984) reported 59 species of mammals in cottonwood riparian woodlands of Colorado,