Rates of spread of the invasive species, cogongrass: Implications for restoration of gopher tortoise habitat

The federally-listed as threatened gopher tortoise (Gopherus polyphemus) depends upon the abundant herbaceous groundcover and open conditions found in remaining fragments of longleaf pine-bluestem forests.  Thus, there is interest in restoring these habitat conditions to many of the pine-shrub forests resulting from fire suppression. Cogongrass (Imperata cylindrica), a non-native grass, threatens habitat quality of these pine-bluestem forests because it provides lower quality forage than most vegetation that it displaces.  To provide information that can assist land managers with habitat management for gopher tortoises on Camp Shelby Training Site, MS, we measured: 1) rates of vegetative encroachment of cogongrass into burned and unburned pine-bluestem and pine-shrub forests and also ruderal areas from 2002 to 2004 and, 2) spikelet dispersal into pine-bluestem and pine-shrub forests.  Burning increased linear encroachment (P = 0.002) and number of cogongrass shoots (P < 0.001) in both forest types.  Mean linear growth during the 2 year period was 220 cm in burned pine-bluestem, 142 cm in unburned pine-bluestem, 175 cm in burned pine-shrub, and 94 cm in unburned pine shrub. By 2004, number of cogongrass shoots was greatest in pine-bluestem burned plots (mean = 84) and least in pine-shrub unburned plots (mean = 8). Spikelets of cogongrass consistently dispersed farther into pine-bluestem (mean =17.3 m) forests compared to pine-shrub forests (mean = 9.4 m; P = 0.004).  Based on these results, efforts to restore pine-shrub forests to pine-bluestem forest conditions should implement control of cogongrass before and after use of fire. In addition, managers will need to be vigilant in their control efforts as restoration efforts shift conditions to those of pine-bluestem forests.