The University of Arizona

Grazing effects on spring ecosystem vegetation of California's hardwood rangelands.

B. Allen-Diaz, R.D. Jackson

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 vegetation surrounding cold-water springs and their downslope creeks. Three spring-creek systems from each of 3 watersheds were randomly assigned to grazing treatments (9 total). Treatments were ungrazed, lightly grazed (1,500 kg(.)ha(-1) residual dry matter), and moderately grazed (1,000 kg(.)ha(-1) residual dry matter) based on degree of use in upland pastures encircling the spring-creek systems. 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 treatment 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 stable. Plant community composition and stability by year and grazing treatment were analyzed with TWINSPAN. With few exceptions, 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 climate interactions until after soil erosion or water table characteristics are seriously, perhaps permanently, altered.

DOI:10.2458/azu_jrm_v53i2_allen-diaz


Keywords


springs (water);ground cover;highlands;species diversity;riparian buffers;body weight;plant communities;California;cattle;plant litter;botanical composition;grazing;dry matter

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