California Oak-Woodland Overstory Species Affect Herbage Understory: Management Implications

Abstract

Concerns for the future of California's oak-woodlands have intensified the need to better understand how different overstory species affect herbage standing crops and species frequencies. Data from over 8,000 plots harvested between 1961 and 1968 at the San Joaquin Experimental Range in the Sierra Nevada foothills of central California show that peak standing crops averaged 2,795 kg/ha in the open; 3,086 kg/ha under blue oak (Quercus douglasii); 1,840 kg/ha under interior live oak (Quercus wislizenii); 1,696 kg/ha under digger pine (Pinus sabiniana), and 1,917 kg/ha under buck brush (Ceanothus cuneatus). Overstory species affected standing crops differently on different range sites. On swales, standing crops were less under live oak and digger pine than in open areas. On open-rolling uplands, standing crops were less in the open and under live oak than under blue oak. On rocky-brush uplands, standing crops were less under all other overstory species than under blue oak. Data on species frequency suggest that herbage species of inter successional stages are more common under trees. The frequency of plant species varied with the species of overstory, and a diversity of overstory species may help to maintain adequate species diversity among understory species.