Influence of Spanish goats on vegetation and soils in Arizona chaparral

Abstract

The key to managing Arizona chaparral depends on creating and maintaining brush-free or savanna-like habitats. Brush control using fire, chemicals, and mechanical methods has been tested previously; but limited information is available on goats. This study evaluated the effect of 4 goat-stocking levels in a short duration grazing system and mechanical brush crushing on chaparral shrubs, herbaceous vegetation, litter, and soils. After 4-1/2 years, percent total shrub cover was lower (P<0.05) on paddocks stocked at 1.4, 2.4, and 4.2 Spanish goats/ha (35, 39, and 382, respectively) compared to unstacked controls (51%). Crushing brush increased the effectiveness of goats; mean total shrub cover was lower (P<0.05) on paddocks where brush was crushed vs not crushed (33 and 50% respectively). Shrubs least preferred by goats were not affected, while preferred browse was impacted at all stocking levels. Goat stocking and brush treatments did not affect perennial herbs, while annuals were generally increased by soil disturbance. Less litter (P<0.05) accumulated under shrubs subjected to heavy stocking levels compared to unbrowsed paddocks. Concentrations of N and P in the soil were also affected (P<0.05) under desert ceanothus (Ceanothus greggii Gray) where the soil bulk density was also increased (P<0.05). While goats can reduce total shrub cover, problems may result. Perennial herbaceous vegetation did not respond. Shrubs preferred by goats were also preferred by native deer. Reduced forage diversity and nutritional stress could result if these species were eliminated from the stand. Also, trampling disturbance by goats affected nitrogen accumulation in the litter and soil, but more importantly heavy browsing may eliminate nitrogen-fixing shrubs