The effects of summer and winter season fires on grass production, woody plant cover, and prickly pear density were studied in the western Edwards Plateau on the Texas AgriLIFE Research Station near Sonora, TX, USA. Years of heavy grazing and fire suppression in the Edwards Plateau region has resulted in the conversion of this former grassland-savanna matrix into a mesquite (Prosopis glandulosa) and juniper (Juniperus spp.) dominated woodland that is difficult to restore. Most research suggests that the sole use of fire to manage invasive woody species, particularly ashe juniper (Juniperus ashei) and redberry juniper (Juniperus pinchotii), will not restore the more productive grassland or savanna ecosystem. We analyzed the long-term response of a heavily invaded savanna to long-term fire treatments applied at the historic fire return interval of six years. We hypothesize that 1) summer fire will reduce juniper and prickly pear cover more than winter fire; 2) summer and winter fire will increase herbaceous production over control (no fire); and 3) repeated burns in the summer will reduce woody plant dominance, thereby producing greater herbaceous production than the winter or control treatments.
Results/Conclusions
Twelve years after the initial fire treatments, the winter fire treatments are more similar to the controls than summer fire treatments. Production of herbaceous plants has increased in the summer fire plots, while biomass has remained relatively unchanged in the winter and control treatments. Similarly, the overstory woody canopy has been reduced by 50% in summer fire plots, whereas cover did not differ over time in winter and control treatments. Such findings suggest that fires conducted at high fire intensities, such as those performed in the summer fire treatments, can shift the competitive balance in favor of grasslands and savannas, whereas fires conducted at low fire intensities (e.g. winter fire treatments) are incapable of accomplishing restoration goals in a stable, juniper woodland ecosystem.
