Effects of Prescribed Burning on King Ranch Bluestem at Vegetative Regrowth and Flowering Stages
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Bothriochloa ischaemum (L.) Keng var. songarica (King Ranch bluestem), an invasive exotic grass dominates native grasses and forbs and endemic species, lowers diversity and alters vegetative habitat structure of plant communities. My study site in the Edwards Plateau ecoregion of central Texas was a generally uniform monoculture of King Ranch bluestem devoid of woody vegetation with slight slope and no channelized drainages, composed of Doss silty clay soils. I compared density, average basal area and total basal area in burned and unburned plots under relatively mild climatic conditions and low fuel load. I assigned four plots to each treatment according to a randomized block design to test the hypothesis that two prescribed fires, selected according to phenological cues associated with low root biomass, would significantly reduce plant vigor and cover. Fire behavior was quantified from measures of flame length and depth and rate of spread. Three mixed-effect models, which treated plot as the replicate and random variable, revealed no significant correlations between treatment type (unburned plots, a burn on 16 July, and a burn on 19 September) and three subsequent measures of King Ranch bluestem plant density and cover (density, P = 0.79; average basal area, P = 0.70; and total basal area, P = 0.48). Because these results showed no correlations, quadrat was then treated as the replicate in subsequent analyses, which also resulted in no correlation between treatment and final measures of density and cover (P = 0.79), average basal area (P = 0.70) and total basal area (P = 0.48). My study presents information for better understanding fire behavior and provides guidance for future research on controlling King Ranch bluestem. In particular, evidence indicates intense fire is likely necessary to reduce density and vigor, regardless of burn date, season or phonological cues.