Population and clonal level responses of a perennial grass following Wre in the northern Chihuahuan Desert

Relationships involving Wre and perennial grasses are controversial in Chihuahuan Desert grasslands of southern New Mexico, USA. Research suggests that Wre delays the resprouting of perennial grasses well after two growing seasons. However, such results are confounded by livestock grazing, soil erosion, and drought. Additionally, post-Wre grass responses may depend on initial clone size. We evaluated the eVects of Wre, grazing, and clone size on Bouteloua eriopoda (black grama) in southern New Mexico grasslands. Four 2-ha plots were established in each of four sites. Fire and grazing were applied or not applied in 1999 such that four treatment combinations were assigned randomly to plots within each site. Within each plot, small (0–10 cm2 basal area), medium (10– 30 cm2), and large ( > 30 cm2) clones were initially mapped in Wve 0.91-m2 quadrats where grass attributes and litter cover were evaluated before and at the end of two growing seasons following Wre. Maximum Wre temperature was also measured. At a population level, canopy and litter cover were each approximately 50% less in burned than unburned areas. However, compared to initial levels, canopy height had increased by 10% at the end of the study, regardless of Wre. At a clonal level, basal cover reductions were attributed mostly to large clones that survived Wre. Smaller clone densities had decreased by as much as 19% in burned compared to unburned areas, and Wre reduced the basal cover of medium clones. Basal and canopy cover, recruitment, and clone basal area decreased with increased Wre temperatures. Almost all responses were independent of grazing, and interactive eVects of grazing and Wre were not detected. Fire did not kill all perennial grass clones, regardless of size. However, rapid responses were likely inXuenced by above-average precipitation after Wre. Future studies in desert grasslands should examine how perennial grass dynamics are aVected by Wre, precipitation patterns, and interactions with grazing.