The effect of fire in a sprayed tobosagrass-mesquite community on Stamford clay soils
In a sprayed tobosagrass-mesquite community, a sere consisting of a sprayed (1966) and of an unsprayed control with burns from 1 to 6 growing seasons old was studied for a wet (1973) and a dry (1974) year on the Rolling Plains of Texas. Spring, summer and fall frequency, density, cover and yield were combined into a relative importance value (I max = 600). Significant species were selected from species which had a frequency analyzable by chi-square (ie <_ 6%). A total of 121 species were collected in the sere, of which 37 in a wet (1973) year and 8 in a dry (1973) year were significant.
Tobosagrass was singularly the most important species. The community was simple because of the importance of tobosagrass. The response to fire in this community was largely the response of one species, tobosagrass, and reaction of other species to it. Tobosagrass and the community after fire reached equilibrium with the sprayed, unburned area by the sixth growing season.
Fire increased the current years growth of tobosagrass. It was about three times higher in the first growing season after the fire than 2 it was in the unburned" area. So biomass increased (Y = a + bX - X^2), yield decreased (Y = a = bX + X^2). They have opposite mathematical functions. Beginning with the yield obtained during the first growing season, biomass and yield from the basis for the horseshoe effect.
Biomass, growth rate, canopy area, height and resprout number were studied with individual plants of mesquite, lotebush and pricklypear. Within six growing seasons, the shrubs had regained at least 70% of all growth measurements compared to the sprayed control. Biomass and growth rate of burned plants reached equilibrium with unburned plants by the sixth growing season. Fire inflicted mortality on mesquite (27%) and pricklypear (55.5%) but no lotebush were killed. Seedlings of mesquite were not observed until the third growing season after the fire.
Fire stimulated microflora activity. The response of the microflora was similar to the response of tobosagrass. They decreased exponentially after the first growing season across the sere until they reached equilibrium with the unburned area during the sixth growing season.
A hypothesis for a mechanism for secondary-autogenic succession following prescribed buming was based on the microenvironmental changes associated with the plant-air layer manipulation. Soil temperature, moisture, infiltration rates, surface plate thickness, organic carbons and nitrogen levels were used with surface litter and percent ground cover to construct the hypothesis. The tobosagrass-mesquite community after burning reached equilibrium as ground cover reached equilibrium (Y = log10X).