Successional Trends in an Ungrazed, Arid Grassland over a Decade

Abstract

A study has been made of the vegetational condition of a formerly grazed area, Chesler Park, in Canyonlands National Park. A comparison was made with the same area 10 years earlier. The lo-year successional changes are also compared to baseline data of 10 years earlier from Virginia Park, an adjacent ungrazed area. Because of inaccessibility and long isolation from disturbances, Virginia Park is presumed to be in climax condition and is the control for this study. Chesler Park shows a successional trend after 10 years toward the vegetational condition of Virginia Park. This is exemplified, with only one major exception (Hilaria jamesii), by responses of the perennial grasses (Stipa comata, Orysopsis hymenoides, Sporobolur cryptandrus, Bouteloua gracilis) and the cryptogamic community, particularly the moss, Torta other areas of Canyonlands had been variously grazed in prior years. The initial study compared the vegetation and soils of Chesler Park with those of an adjacent, but smaller (97ha) ungrazed area, Virginia “Park.” The access to Virginia Park is impassable for cattle or horses due to high rock walls and therefore the area remains relatively undisturbed. For this reason results of this initial study provided an invaluable source of baseline data against which future vegetational changes in grazed areas can be compared. Gross environmental characteristics vary little between the two parks. The climate of the area is semiarid to arid. It is a country of extremes with an annual temperature range of as much as 55’ C. Annual precipitation is generally from 20 to 25 cm, of which warm season rainfall constitutes from 55$&-75% of the total. Although overall park attendance has increased significantly during the decade (Wylie 1981) the study areas have remained relatively isolated-Chesler Park was closed to vehicular traffic in 1971, and Virginia Park, because of its inaccessibility, has never been subjected to such traffic. Both areas are now accessible only The author is with the Department of Biology, University of Nevada-Rena,, Reno 89557. Appreciation is extended to the Research Advisory Board, University of NevadaReno, for financial support of a portion of this study; also, to the ranger staff of Canyonlands National Park for the hospitality provided. Manuscript received March 27, 198 I. 114 by foot and, because of their remoteness, this usage is considered to be moderate. The purpose of this study was to investigate vegetational and fioristic changes over a decade in an area which had been formerly grazed and to compare the decadeend condition with that of a similar, adjacent area which had not been formerly grazed. Data were collected in 1977 from 20 sites in Chesler Park for comparison with those from 20 Chesler sites in 1967. The 1977 composition is also compared with the undisturbed and presumably climax condition of Virginia Park in 1967.