A herd of translocated and resident pronghorn meander through the Marfa Plateau.

Prescribed Fire and Pronghorn Habitat

Forbs are an important dietary component for many wildlife species, including pronghorn, which consume forbs as their primary food source. The precipitous decline of pronghorn in the Trans-Pecos has inspired recent research examining habitat improvement for this species, including the use of prescribed fire as a method of increasing forb quantity and diversity.

Research, rainfall and recovery.

We evaluated vegetation on several sites on three Brewster County ranches where prescribed burning has been utilized as a management tool. On all three ranches, areas were available allowing for examination of vegetation characteristics on unburned (control) sites; on very recently burned sites following green-up; and on sites, one, two, three, and four years, post-burn. Analyses were made for forbs, for herbaceous species in general, and for woody vegetation. We also considered the effects of grazing and variable precipitation, including the lack of the latter during the exceptional drought of 2011.

Each prescribed fire has the potential to produce unique results given differences in relative humidity, temperature, soil moisture, live fuel moisture, wind velocity, and fine and woody fuel loads. On our study sites, we noted an overall decline in herbaceous vegetation where grazing was present, due in large part to a preference of cattle for highly palatable new growth over old, dead, or dormant growth. Where grazing was absent or minimal, standing biomass was more similar to controls.

Forb diversity and density seemed as dependent upon precipitation and grazing as on fire effects and both increased on grazed areas following prescribed burns. Cattle hoof impacts can compact litter, the accumulation of which inhibits herbaceous plant growth. Cost-analysis suggests that prescribed burning to increase forb production may be as or more effective than mechanical or chemical treatments. Grazing on burned sites may need to be deferred or limited, especially during drought years, but can be used to extend the increase in forb diversity and density after fire.