Mesquite savanna development using low-intensity fires and Reclaim herbicide

Introduction Mesquite in dense thickets reduce grass production and make livestock management more difficult. To compound the problem, treatments which top-kill mesquite, such as chaining, shredding, high-intensity fires, or herbicides such as 2,4,5T or triclopyr (Remedy), stimulate regrowth from stem bases and increase stem number per plant and per land area (Fisher et al. 1959). An alternative strategy may be to manage for a "mesquite savanna", or a grassland with a low density of taller trees. The mesquite savanna offers a middle ground between maximizing benefits while minimizing negative effects of this species (Jacoby and Ansley 1991). Mesquite may enhance soil fertility by nitrogen fixation. Plant species diversity often is enhanced because growth of some grasses, shrubs and forbs are better beneath mesquite canopies than in open spaces. A mesquite savanna may enhance wildlife habitat over open grassland alone and optimizes a multiple use strategy of livestock and wildlife production (Fulbright 1997). The savanna option may provide sustainable ecological and economical productivity while minimizing management and maintenance costs. The tactical goal for savanna management would be to reduce density of thickets to some "moderate" level, yet maintain the upright growth form of remaining mesquite. Fire may accomplish such a goal iffireline intensity is low enough so as to not top-kill the larger mesquite, yet sufficient to top-kill or possibly root-kill the smaller mesquite. Another treatment which has potential for mesquite savanna development is a low rate of Reclaim (clopyralid) herbicide. Use of clopyralid alone has been observed to root-kill some mesquite, but surviving plants usually have "stem flagging" in which portions of the canopy foliage survive (Jacoby and Ansley 1991). The remaining foliage on stem-flagged mesquite may exert apical dominance and prevent sprouting from stem bases. Our objective was to examine the potential oflow-intensity fires and a low rate of clopyralid herbicide to convert mesquite thickets into savannas. Specific hypotheses were: (I) lowintensity fires or a low rate of clopyralid will achieve the thicket-to-savanna objective by achieving a moderate (i.e., 20 to 40%) level of top-kill and root-kill, and (2) repeated lowintensity fires are more effective than single low-intensity fires in achieving the thicket-to-savanna objective.