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 dougkr-s&l,840 kg/ha under interior live oak (Quercus wislizenii); 1,696 kg/ha under digger pine (Pinussabiniana); 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 later 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.

Effects of Quercus emoryi on herbaceous vegetation in a semi-arid savanna

“…Decreased understory biomass under trees has been attributed to competition for light (Duncan et aL 1983;Parker & Muller 1982) and soil water (Tiedemann & Klemmedson 1977;Smith & Stubbendieck 1990), allelopathy (Muller & Muller 1956;Lodhi 1978;Engle et al 1987;Ratliff et al 1991), interception of precipitation by overstory (Schott & Pieper 1985), and litter accumulation (Lodhi 1977).…”

Aspen canopy removal and root trenching effects on understory vegetation

“…According to this theory, facilitation is always present, but is masked in more productive or low disturbance environments by a greater impact of competition. Limited evidence from field research supports the general pattern of net facilitation from an overstory under conditions of environmental extremes (Belsky, 1994;McClaran and Bartolome, 1989;Ratcliff et al, 1991). However, facilitation theories have not been widely tested, nor are the base assumptions and associated hypotheses universally accepted.…”

Review. Impact of grazing on plant communities in forestry areas

“…These populations usually accumulate a considerable amount of acidic litter resistant to decomposition. A clearing of the pine litter as a result of animal consumption and trampling (Torrano and Valderrábano, 1999) would not only increase the chances of plants emerging, but also help the germination of species inhibited by the acidity of the soil (Ratliff et al, 1991). From the point of view of fire prevention, the clearing of the litter would reduce the probability of ignition occurring in these communities, which otherwise would be at considerable risk (Tsiouvaras et al, 1989).…”

“…The use of other clearing techniques (mechanical or chemical) is not always effective Table 2. Some characteristics of competitive, stress tolerant and ruderal plants (Grime, 1977) at increasing the density of herbaceous plants ( Morton and Melgoza, 1991;Bartolomé et al, 1994;Nolte and Fulbright, 1997) either due to the influence of topo-edaphological (Archer and Smeins, 1991) and climatic factors (Bozzo et al, 1992;Bartolomé et al, 1994), and to the influence of the dominant shrubby vegetation (Ratliff et al, 1991) on the response of herbaceous plants to shrub control.…”