PARENT SESSION
Oral Session # 52: Fire Ecology III: Grasslands; Scrub.
Presiding: J Grace
Wednesday, August 6. 1:30 PM to 5:00 PM, SITCC Meeting Room 102.
The effect of fire on a mixed Chihuahuan Desert plant community.
McKernan, Pamela*,1, White, Joseph1, Gutzwiller, Kevin1, Barrow, Wylie2, Randall, Lori2, 1 Baylor University, Waco, TX2 U.S. Geological Survey, Lafayette, LA
ABSTRACT- The effect of fire on plant community composition and successional response was investigated in Big Bend National Park, Texas (1) locally by observing the short-term response of vegetation within a 500ha prescribed burn and (2) regionally through land cover change analysis using Landsat-5 Thematic Mapper (TM) data. We predicted that fire intensity and severity within this patchy fuel environment would reduce overall shrub densities and promote grass establishment. Predictions of long-term community changes were based on trends observed between Landsat TM images of 1986 and 1999 and on seed bank analyses. Within the burn sites, the pre-fire characterizations of fuel distributions and vegetation cover indicated a shrub-dominated community with disconnected fuels and vegetation canopies. Seed pools also indicated higher proportions of shrub species. Surface fire temperatures, rates of spread, and post-fire severity ratings were related to fuel patchiness and pre-fire species composition. Post-fire seed banks did not change appreciably due to the low intensity of the burn. Shrubs were most reduced by the prescribed burn, while site patchiness was significant in determining mortality rates. Analysis of landcover change from Landsat TM derived vegetation maps between 1986 and 1999 indicated a region-wide proliferation of shrub communities. Comparison of burned and unburned areas in the park showed no difference in the rate of landcover change suggesting a negligible impact of fire in patchy shrub dominated communities. This supports the idea that the occurrence of a single fire in an extremely patchy fuel and vegetative environment may not be sufficient in changing community composition.
Key words: desert, fuels, fire, Landsat