Interactions between thinning and bear damage complicate restoration in coast redwood forests

Abstract

Silviculture was used to direct the development of young redwood stands toward old forest stand structures. Two variable-density thinning treatments and an unthinned control treatment were monitored for 10 years following treatment in young coast redwood (Sequoia sempervirens) stands in northern California, USA. The intent of these treatments was for forest restoration by accelerating the development of old forest features. The thinning treatments increased individual tree growth in both low and moderate density thinning treatments as compared to the control. The variable-density thinning also resulted in greater stand structural variability and was successful at increasing the relative proportion of redwood. Black bears (Ursus americanus) caused major damage to residual trees and showed a preference for more vigorous trees. Most of this damage occurred in the first four years after thinning. The confounding effects of thinning to favor larger trees and bear damage preferentially affecting more vigorous and large trees reduced the effectiveness of these treatments by eliminating the stems intended to form the future old forest structures. It also indicates forest managers need a conservative approach that leaves greater numbers of residual trees in redwood stands when bears are present. Thinning should leave sufficient trees to form the old forest structure plus ample allowances for bear-caused mortality. The long-term outcome of stand development in these thinned redwood forests is uncertain because of high rates of mortality in young trees.