Vegetation response to the Santa Rita grazing system

Abstract

Changes in vegetation under yearlong grazing were compared with those under the Santa Rita grazing system, a rotation system designed for southwestern US rangelands where 90% of the forage is produced in mid- to late-summer. The study was conducted on the Santa Rita Experimental Range near Tucson, Arizona, from 1972 to 1984. In 1984 there were no differences (P<0.05) in grass densities (16 vs. 17 to 18 plants/m2), forb densities (0.6 vs 0.7 to 1.4 plants/m2), shrub densities (2.0 vs 1.9 to 2.4 plants/m2), or shrub cover (20 vs 21 to 26%) on pastures grazed yearlong or in the Santa Rita rotation, respectively. Lack of response to grazing schedules is attributed to initial plant densities near the maximum the sites could support and to moderate grazing during the study period. Average herbage yields of pastures were not related significantly to grazing treatments but correlated strongly (r = 0.909) with long-time summer rainfall means. Results support the observation that rotation grazing may not improve ranges that are in good condition. It is concluded, however, that the Santa Rita Grazing System may accelerate recovery of ranges in poor condition.