Environmental limits of an endemic spruce, Picea breweriana

Abstract

Brewer spruce (Picea breweriana Wats.) persists as a relict in protected physiographic situations in southwestern Oregon and northwestern California, where a cool, montane, temperate zone inland from the Pacific Ocean is moderated in summer by maritime air masses. We attempted to uncover the reasons for its survival. We surveyed the species distribution and geologic and floristic associations, then studied effects of environment on growth and survival of two widely distributed species, Pseudotsuga menziesii (Mirb.) Franco and Abies magnifica Murr. var. shastensis Lemm., for a common basis for comparison. The survey included 130 plots along a 250-km transect. Brewer spruce was encountered along 70 km of the transect. Brewer spruce ranked well with other conifers in tolerance to soil moisture stress, cold temperatures, low light, and heavy, deep snow. Although sensitive to high evaporative demand, it appears to compete well with sparse vegetation in infertile or unbalanced soils developed from ultrabasic materials.