SOILS OF THE RED FIR FOREST-BARRENS MOSAIC, SISKIYOU MOUNTAINS CREST,CALIFORNIA

In the crest areas of northern California and southern Oregon mountain s, Shasta red hr (Abies magnifica var. shastensis Lemmon) forests are often interspersed with irregularly shaped, 0.1- to 50-ha openings tha t contain only sparse prostrate forbs and sub-shrubs amid mostly bare and gravel-paved soil. We investigated these forest-barrens associatio ns to determine if soil differences could help explain the cause of th e barrens. While the soils (Xerumbrepts) are morphologically similar i n many respects, burrowing by abundant pocket gophers (Thomomys sp.) i n the barrens produced thicker umbric epipedons than in the forests, w here pocket gophers are absent. The only significant soil chemical dif ferences detected between sites were loner concentrations of Ca and Mg in the barrens surface soils. In contrast, base cations accumulate in the forest A horizons as a result of biocycling. While the origin of the barrens remains unknown, herbivory by pocket gophers is a major fa ctor in maintaining the barren conditions and their activity ultimatel y accounts for most soil chemical and morphological differences.