HERBAGE RESPONSE FOLLOWING CONTROL OF HONEY MESQUITE WITHIN SINGLE TREE LYSIMETERS

Justification for controlling honey mesquite (Prosopis glandulosa Torr. var. glandulosa) on rangelands has been traditionally related to enhanced livestock production from increased herbage production. More recently, however, it has been hypothesized that control would also increase off-site water yield. The objective of this 3-year study was to quantify the effects of control of individual honey mesquite trees inside nonweighable lysimeters on herbage standing crop, leaf area, and aboveground production. Utilizing frequent harvest techniques, estimated aboveground net primary production (ANPP) in intact tree lysimeters averaged 235 g/m2. Estimated ANPP in the treated lysimeters averaged 349 g/m2. The increased ANPP, following removal of the trees, resulted in significantly greater amounts of herbaceous leaf area and standing crop. The increase in ANPP was relatively uniform regardless of distance from the trunk of removed trees and was the result of increased production by those herbage species present at time of control rather than a shift in species composition. The dominant species in both treatments was Texas wintergrass (Stipa leucothrica Trin. & Rupr.). Sideoats grama [Bouteloua curtipendula (Michx.) Torr.] was a subdominant. The results, in combination with concurrent water yield studies, suggest control of honey mesquite will not enhance water yields dramatically in this region in the absence of livestock grazing.