PARENT SESSION
Oral Session #55: Fire Ecology. Presiding: M. Moritz.
Wednesday, August 8, 2001. 1:00 PM to 5:00 PM. Hall of Ideas H.
Fire effects on plant diversity in serpentine versus nonserpentine chaparral and grassland.
Safford, Hugh1, Harrison, Susan1, 1
ABSTRACT- Fire contributes to the maintenance of species diversity in many plant communities; however, few studies have assessed the comparative importance of fire in similar communities that vary in such attributes as soils and productivity. Soils formed from serpentine rock are low in productivity and support a rich flora of native and endemic plants in California. We studied the effects on diversity of a wildfire that occurred in a mosaic of chaparral and grassland vegetation on serpentine and nonserpentine soils. We hypothesized that because biomass is lower on serpentine, space and light are less limiting, and therefore postfire increases in plant richness and diversity would be lower in serpentine than the corresponding nonserpentine plant communities. We compared the magnitude of fire-associated changes in species diversity between serpentine and nonserpentine soils, within each community type, chaparral (N = 80 sites) and grassland (N = 100 sites). In chaparral, we paired burned and unburned sites and measured covariates to ensure that sites did not otherwise differ; in grasslands, we controlled for prefire variation using baseline data from a previous study. In chaparral, the diversity of both native and exotic species increased more in response to fire on nonserpentine than serpentine soils, at both the local (250 sq. m) and regional scales. In serpentine chaparral, specialized fire-following species were less prevalent, mean and maximum fire intensity were lower, and mean time since last fire was longer than in nonserpentine chaparral. Within each soil type, fire responses were positively correlated with measures of soil fertility. In grasslands, fire did not affect native species richness on either soil, but caused an increase in the richness of exotic species on nonserpentine soil at both the local (5 sq. m) and regional scales. Livestock grazing was associated with a similar and independent increase in exotic species richness in nonserpentine grasslands, as well as a decrease in the regional richness of natives. Our results suggest that fire may occur predictably but less frequently, and may play a less pronounced role in the maintenance of diversity on serpentine than nonserpentine soils.
KEY WORDS: fire, species diversity, productivity, serpentine