Some Factors Affecting Twig Growth in Blackbrush

Abstract

Domestic goat browsing was used to stimulate twig production by blackbrush. Precipitation, soil depth and stoniness, branch location, and the number of years of browsing and rest from browsing affected twig production (P<0.05). As precipitation doubled, production increased by a factor of 1.9. Twig production by plants growing on deep soils (71 cm) was 1.9 times that by plants growing on shallow soils (39 cm). Older branches growing on the outer edges of blackbrush plants (terminal branches) produced 4.6 times more current season's twigs than sprouts and young branches (basal branches) growing within the shrub canopy. Heavily browsed plants increased twig production by a factor of 3.6 relative to control plants, and production remained at this level, even after 4 consecutive years of browsing. Annual twig production declined with rest from browsing. However, plants that were browsed and subsequently rested for 2 years yielded an aggregate 1.6 times more available forage than plants that were browsed on a yearly basis. This was due to an accumulation of twigs ranging in age from 1 to 3 years.