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<br />56
<br />
<br />~iparian Ecosystems and the Edge Effect
<br />
<br />The large nWllber of vertical and horizontal strlltll caused by riparian
<br />zone vegetation and the associated high productivity, l;pecies diversity and
<br />densitj"are collectively known as the "edge effect" (FIgure 2). Those
<br />species which occur primarily, are 1Il0st-aiiUndant or spE!lld the greatest
<br />amount of time in the ecotone are called "ed.~ species."
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<br />(Modified frolll ThOllla8 H d. 1979)
<br />
<br />The dramatic contrasts between the vegetative complex of the riparian
<br />zone and that of the adjoining aquatic and terrestrial zones add to the
<br />structural diversity of the riparian co~~unity. Wetlands, ponds, oxbow
<br />lakes, seeps, springs and minor drainages provide edges of stark contrast
<br />to the surrounding semiarid or arid zones. Moreover, riparian zones
<br />dominated by deciduous vegetation provide on,e, type of h,sbitat during
<br />leaf-out aonths and another type of habitat dluring the 'dnter following
<br />leaf-fall. The meandering shape and linear nature of the riparian zones
<br />maximize the development of the edge effect and edge sp,ecies. Riparian
<br />zones in semiarid and arid regions produce f,.,r more edg,"s within a small
<br />area than would be expected or found in the ,adjacent sagebrush terrestrial
<br />zones (Figure 3).
<br />
<br />Functional Definition of Rip~!!an Vegetl~
<br />
<br />Riparian ecosystems are characterized bl' stream bank vegetation with
<br />more hydric or mesic (i.e., moderately moist) growth habits than adjacent
<br />, drier upland plant communities. All riparian plant comDlunities are
<br />'--dependent upon high water tables or overbank flooding tel meet their
<br />l10isture requirements. They may also depend on overbank flooding for the
<br />deposition of substrates and nutrients necessary for regeneration,
<br />establishment and maintenance.
<br />
<br />Functionally, riparian ecosystemS strongly influence adjacent ..quatic
<br />zones. To a large extent, the riparian zone regulates the productivity of
<br />, the aquatic zone by supplying organic detritus in the form of leaves,
<br />\~tems, twigs, branches, etc. to the stream. ~rhis has prompted SOme workers
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