Despite extensive coverage and long-term use, the extent to which shad
scale [Atriplex confertifolia (Torr. & Frem.) Wats.] community dynamic
s are driven by grazing rather than by climate and inherent plant char
acteristics is unresolved. We analyze a 59-year data set from the Dese
rt Experimental Range, southwestern Utah, with the objective of discri
minating between grazing and non-grazing effects on cover dynamics. Ca
nopy cover of (5 x 20 ft) 9.3 m(2) plots were estimated in 1935, 1958,
1969, 1975, and 1994. Treatments were time (5 dates), grazing (ungraz
ed versus grazed), and season (spring versus winter). Time was signifi
cant; total cover initially increased following release from uncontrol
led grazing and improvement of climate (1935-58, P < 0.001), remained
unchanged over the following dry interval (1958-69, P = 1.000), increa
sed over a drier interval (1969-75, P < 0.001), and then decreased dra
matically over the final wet period (1975-94, P < 0.001). Grazing was
also significant (P < 0.001), but cover of ungrazed plots exceeded tha
t of grazed plots only in 1975 and 1994 (P less than or equal to 0.033
). The 6 dominant species showed varying responses to grazing and time
, with some responding primarily to grazing (e.g., budsage, Artemisia
spinescens D.C. Eaten in Wats.) and others responding primarily to tim
e (climate, longevity, etc., e.g., Indian ricegrass, Oryzopsis hymenoi
des R & S). Similarly, seasonal effects were not universal. Shrub cove
r initially increased and then declined dramatically while grass cover
monotonically increased. Results suggest that release from uncontroll
ed grazing coupled with improving climatic conditions were responsible
for initial recovery of the community, but that over time, climate an
d inherent plant traits (e.g., longevity, establishment ecology, etc.)
became relatively more important. For total cover and for many indivi
dual species, continued grazing affected the rate more than the direct
ion of vegetation change.