Soil properties important to the restoration of a Shasta red fir barrens in the Siskiyou Mountains

Abstract

Because of past major disturbances, the highly erodible, granitic soil in a Shasta red fir ( Abies magnifica A. Murr. Var. shastensis) barrens located in McDonald basin on the north side of the Siskiyou Mountains crest is a major contributor of sediment to the aquatic system. Soil erosion is accelerated where vegetation is sparse and colonization slow, therefore, it is important that native plant cover be restored and the site rehabilitated. We examined soil properties that may be associated with vegetation patterns in the barrens and adjacent Shasta red fir forest and would have application to restoring native plant diversity and cover to the barrens. At a 40 ha study area we investigated plant available nutrients, soil C, microbial biomass, and enzymes involved in organic matter decomposition and nutrient cycling in barrens and forest soils to determine if loss of the organic layer by erosion affected soil chemistry and microbiology. Twelve samples each were collected from 0 to 10 cm soil depth in forest and barrens and analyzed for C, N, P, K, Ca, Mg, Mn, Fe, Cu, B, Zn, Mo, and Al; microbial biomass, and dehydrogenase, urease, and acid phosphatase activity. Soils supporting forest vegetation contained higher concentrations of C, N, K, Ca, and Mg, indicating differences between forest and barrens in important soil chemical properties. Ca and Mg were extremely low in the barrens soil suggesting loss of these nutrients by erosion where there is a lack of vegetation cover. Soil organic matter was higher in forest than in barrens soil and was positively correlated with soil N ( r 2=0.78), dehydrogenase ( r 2=0.65) and acid phosphatase activity ( r 2=0.50). Although microbial biomass was extremely low, dehydrogenase and acid phosphatase activity were sensitive indicators of differences in organic matter and microbial activity between forest and barrens soil. The study indicates that certain soil chemical and biological properties may be useful in monitoring ecological change and helpful in understanding vegetation patterns.