Anthropogenic and natural disturbance and patterns of mortality in a mixed conifer forest in California

Abstract

Anthropogenic and natural disturbances have been implicated in recent mortality episodes in montane forests. While the role of natural disturbance in patterning forest ecosystems has been widely explored in recent decades, the agency of human influence is less well understood. In this paper, stand structure analysis is used to characterize patterns of mortality in a montane mixed conifer forest in southern California subject to multiple influences, both anthropogenic and natural, including fire suppression, air pollution, drought, competition, and insect infestation. While it is difficult to separate the contribution of any one of these factors to tree death, because there have been cumulative and synchronous disturbances, successional trends can be identified. Anthropogenic influences appear to abet the effects of natural disturbance in enhancing the shift from early successional pines to species that tolerate stresses such as drought, fire suppression, or competition that result from increased stand density, or a combination of such stresses.