Stability of C3 and C4 grass patches after fire and simulated grazing

As the woody legume, Prosopis glandulosa (honey mesquite) has encroached into grasslands and rangelands in the southern Great Plains, USA, two grass species, C4 shortgrass, Buchloe dactyloides (buffalograss), and C3 mid-grass, Nassella leucotricha (Texas wintergrass), have increased in dominance. Occurrence of more productive C4 mid-grasses and herbaceous diversity have declined. We measured effects of various combinations of spring clipping (to simulate cattle grazing) and summer and/or winter fire treatments on the stability of monoculture patches of these two grass species over an eight-year period, with the goal of reducing Nassella and increasing C4 mid-grass cover. All fire treatments top-killed most Prosopis trees that subsequently resprouted. Buchloe cover declined in the No Clip + No Fire treatment but remained intact with clipping and/or fire. Frequent clipping reduced Nassella cover across all fire treatments. Buchloe encroachment into Nassella patches was greatest in the Clip + Alternate Season fire treatment. C4 mid-grass cover increased to 15–25% in Nassella patches in several fire-only or Clip + Fire treatments; greatest gains were observed in treatments that included summer fire. In contrast, C4 mid-grass gains were lower in Buchloe patches. These results suggest that C4 mid-grass restoration was linked with treatments that reduced Nassella cover.

Methods
Data were collected in a field study in north central texas, USA, after plots were exposed to dufferent prescribed fire treatments and/or clipping treatments to simulate grazing. All data were collected over a 9-year period of time. Field observations of ground cover of different grass species, forbs, litter and bareground were recorded in the field, verified with photographs of 0.5 x 1.0 m small plots, and entered into an excel spreadsheet for analysis.