Grazing Effects on Spring Ecosystem Vegetation of California's Hardwood Rangelands

Abstract

Three watersheds at the University of California's Sierra Foothill Research and Extension Center (SFREC), Marysville, Calif. were selected to study cattle grazing effects on the vegeta - tion surrounding cold-water springs and their downslope creeks. Three spring-creek systems from each of 3 watersheds were ran- domly assigned to grazing treatments (9 total). Treatments were ungrazed, lightly grazed (1,500 kgha -1 residual dry matter), and moderately grazed (1,000 kgha -1 residual dry matter) based on degree of use in upland pastures encircling the spring-creek sys - tems. Total herbaceous cover at springs varied significantly among the 6 years only once (greater in 1994 than all others) covarying with previous year's rainfall. Grazing intensity did not affect total herbaceous cover at springs. A year X grazing treat - ment interaction (P<0.05) was detected for total herbaceous cover at spring-fed creeks. Three years after grazing removal, total herbaceous cover on ungrazed creek plots surpassed cover at moderately grazed and lightly grazed plots. Moderately grazed plot herbaceous cover declined steadily throughout the first 3 years, while lightly grazed cover remained relatively sta - ble. Plant community composition and stability by year and graz - ing treatment were analyzed with TWINSPAN. With few excep- tions, stable plant communities persisted on sites regardless of grazing intensity or cover changes. Total herbaceous cover was sensitive to interannual fluctuations, especially under increased grazing intensities. This attribute renders cover a more useful gauge of ecosystem health than plant composition as the latter may not provide evidence of potentially deleterious grazing X cli - mate interactions until after soil erosion or water table charac- teristics are seriously, perhaps permanently, altered.