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Soils of the Red Fir Forest-Barrens Mosaic, Siskiyou Mountains Crest, California

U.S. Forest Service, Klamath National Forest, 1312 Fairlane Rd., Yreka, CA 96097

R.C. Graham and K. R. Tice

Dep. of Soil and Environmental Sciences, Univ. of California, Riverside, CA 92521-0424

* Corresponding author.

ABSTRACT

In the crest areas of northern California and southern Oregon mountains, Shasta red fir (Abies magnifica var. shastensis Lemmon) forests are often interspersed with irregularly shaped, 0.1- to 50-ha openings that contain only sparse prostrate forbs and sub-shrubs amid mostly bare and gravel-paved soil. We investigated these forest-barrens associations to determine if soil differences could help explain the cause of the barrens. While the soils (Xerumbrepts) are morphologically similar in many respects, burrowing by abundant pocket gophers (Thomomys sp.) in the barrens produced thicker umbric epipedons than in the forests, where pocket gophers are absent. The only significant soil chemical differences detected between sites were lower 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 factor in maintaining the barren conditions and their activity ultimately accounts for most soil chemical and morphological differences.

Received for publication October 6, 1993.