COS 119-7
Interactive effects of prescribed fire and grazing on woody encroachment and invasive grass abundance in a south Texas coastal prairie
Developing effective restoration techniques for coastal prairies degraded by woody encroachment and invasive introduced grasses requires an understanding of two fundamental ecological processes: fire and grazing. Prescribed fire and grazing are recommended for suppressing non-native species that are functionally distinct from the native prairie they invade. However, in south Texas, exotic C4 grasses (Bothriochloa ischaemum and Dichanthium sericeum) invade native C4 prairies. Comprehensive examination of non-native grass response to fire and grazing is needed, given the functional similarity of the natives and non-natives in this system. We established a full-factorial, completely randomized experiment on an encroached prairie in south Texas to examine the interactive effects of seasonal prescribed fire and ungulate grazing on invasive grass abundance, herbaceous community diversity, and woody vegetation density. We randomly assigned six treatments to 36 10mX10m plots including: i.) summer burned and fenced ii.) summer burned and unfenced iii.) winter burned and fenced iv.) winter burned and unfenced v.) unburned and fenced vi.) unburned and unfenced . We conducted independent prescribed fires in August 2013 and February 2014. Each season of burn treatment was followed by a two month rest period and two month grazing rotation.
Results/Conclusions
Results from vegetation sampling conducted two months after treatment applications suggest that summer prescribed fire may decrease shrub height and canopy cover and increase total stem counts across all shrub species. Total percent foliar cover of all shrubs in summer burned plots decreased. Leaf litter cover increased and bare-ground decreased in grazed plots. There were no significant interactions between summer burned and grazed plots on shrub height, stem count, or canopy cover. Percent utilization was similar in both summer burned and unfenced (grazed) plots and unburned fenced plots. Assessing plant community responses to prescribed burn season in combination with grazing will provide important insights into the factors influencing woody vegetation dynamics and invasive grass growth and survival. Sampling of these plots in subsequent growing seasons and comparing vegetative responses to summer vs. winter prescribed fire will reveal whether certain seasons of fire are more effective at controlling re-sprouting shrubs and invasive grasses.