Differences in Riparian Vegetation Structure between Grazed Areas and Exclosures

Abstract

The valuable role that healthy riparian ecosystems play in regional diversity of plant and wildlife communities is just beginning to be recognized. Resource managers need to know how degraded riparian areas respond to changes in management, such as reduction and elimination of grazing. Differences in vegetation structure were examined in a montane riparian zone in northcentral Colorado after 30 years of cattle exclusion and continued, but reduced, grazing pressure. In order to assess the changes in the riparian community, canopy coverage, density, and standing crop of important riparian species were measured in 1985 and 1986. Total vascular vegetation, shrub, and graminoid canopy cover was greater (P?0.05) in the exclosures as compared to grazed areas, while forb canopy cover was similar (P>0.05) between treatments. Exclosures had nearly 2 times the litter cover, while grazed areas had 4 times more bare ground. Willow canopy coverage was 8 1/2 times greater in protected areas than in grazed areas. Kentucky bluegrass (Poa pratensis L.) cover was 4 times greater in grazed areas than exclosures, while the cover of fowl bluegrass (Poa palustris L.) was 6 times greater in the protected sites. Canopy cover of other important riparian species, such as tufted hairgrass (Deschampsia caespitosa (L.) Beauv.), Nebraska sedge (Carex nebraskensis Dewey), and beaked sedge (C. rostrata Stokes), was similar (F>0.05) between treatments. Mean peak standing crop over the 2 years of the study ws 2,410 kg/ha in the exclosures and 1,217 kg/ha in caged plots within grazed areas. Cattle utilized approximately 65% of the current year's growth of vegetation during the 1985 and 1986 grazing seasons. Riparian areas provide habitat for wildlife and fish species, while providing forage for domestic livestock. These areas provide a diversity of foraging and breeding sites that permit coexistence of many wildlife species. Intact aquatic ecosystems with abundant streamside vegetation insure healthy fish populations (Kauffman and Kreuger 1984). Improper livestock use of riparian areas can increase erosion and reduce plant vigor, resulting in lowered forage production and altered plant age structure and species composition (Knopf and Cannon 1982, Kauffman and Krueger 1984, Skov