USA — The effects of burning on rangelands have long been debated. Although it is desirable to remove woody plants and invasive species, fire may also eliminate the native grasses that are important for raising cattle. Studying the effects of burning over a span of years can inform land managers how rangelands will respond to this type of management.
The current issue of the journal Rangeland Ecology & Management describes a 12-year study of a semiarid live oak savanna in Texas. Savannas such as these are transitioning from landscapes dominated by grass and trees into shrub-dominated woodlands. This new face of rangeland ecosystems is neither aesthetically nor economically desirable given the rate and extent of its occurrence.
Human actions have brought about many alterations in rangelands. Global expansion of the cattle industry has caused displacement of native grazers and has contributed to overgrazing. These activities reduce the growth of herbaceous plants that provide fuel , which reduces fire intensity and limits fire effectiveness in eliminating woody plants.
Historically, fires swept the savanna of the Edwards Plateau region of Texas about every six years. This long-term fire study mimicked the historical cycle. Between 1994 and 2006, summer and winter burns were conducted every six years. The results of these burns and a controlled unburned area were compared and contrasted.
Repeated high-intensity summer burnings reduced or eliminated encroaching woody plants such as prickly pear cactus, juniper, and mesquite. With less intense winter burnings, undesirable woody plants tended to maintain their presence on the savanna, but their spread was restricted. Among herbaceous grass species, little bluestem increased following winter burns and remained constant after summer burns. Weather and other variables had greater effect on other grasses than did burning treatments.
The study found that fire can reduce woody plant species without having a long-term, negative effect on desired grasses. While the burned areas showed positive results in their regrowth, the unburned control area of land rapidly transitioned from a grass-and-tree savanna into woody domination.