Document: JOD-3-69-26

Fire suppression, tree encroachment, and the spread of exotic species threaten the persistence of two endangered plants in California.

MCGRAW, J.M.*

University of California, Berkeley, CA 94720, U. S. A. ¹

Abstract:
In many terrestrial plant communities, fire promotes coexistence and enhances diversity by removing dominant woody vegetation. While fire suppression has altered community structure in many fire-prone communities, efforts to restore natural fire regimes may fail due to community changes during the period of suppression. Of particular concern is the presence of exotic species not historically in the system. In the unique, edaphic sandhills community in central coastal California, fire suppression has allowed for the encroachment of Pinus ponderosa. The spatial distribution of herbaceous plants, including that of two endangered species (Chorizanthe pungens var. hartwegiana and Erysimum teretifolium), is negatively correlated with the presence of trees. To examine the mechanisms by which Pinus inhibits Chorizanthe and Erysimum, I conducted a factorial experiment testing the effects of shade, leaf litter, and proximity to trees on the germination, survivorship, growth, and reproduction of the endangered species. The results indicated that leaf litter has an over-riding negative effect on the demographic success of both Chorizanthe and Erysimum. While the reintroduction of fire to reduce tree density and remove accumulated litter may benefit Chorizanthe and Erysimum, it may also facilitate exotic species which have been shown to have strong competitive effects on the native plants. A subsequent small-scale burn experiment to examine these hypothesized direct and indirect effects of fire on Chorizanthe and Erysimum showed that fire enhances natural community diversity by disproportionately killing exotic species.

Keywords: fire, exotic species, endangered plants

This abstract is being presented at: 4:45 PM in session:
Oral Session #33: Plant Demography.