Tree canopy effects on herbaceous production of annual rangeland during drought

Abstract

Seasonal herbaceous production was measured beneath tree canopies of blue oak (Quercus douglasii Hook & Arn.), interior live oak (Quercus wislizenii DC), and digger pine (Pinus sabiniana Dougl.), and in adjacent open grassland during 2 drought years (1986-87 and 1987-88) at the San Joaquin Experimental Range, California. Early and mid-growing season herbaceous production was variable, with no increase in production beneath the canopies the first year and a 60 to 150 kg/ha increase the second year compared to the herbage produced in open grassland. Peak standing crop was about 1,000 kg/ha greater beneath blue oak canopies than in open grassland in both years. Peak standing crop beneath interior live oak canopies was about 700 and 1,000 kg/ha greater than in open grassland the first and second years of the study, respectively. Peak standing crop beneath digger pine canopies was about 500 kg/ha greater the first year and similar the second year to that of the open grassland.