Effects of wildfire severity and post-wildfire management actions on vegetation recovery trajectories in the Lost Pines of Texas

Background/Question/Methods

The Lost Pines of central Texas are the westernmost stands of loblolly pine (Pinus taeda) in the United States. They support a diverse native plant community and are the habitat of the endangered Houston toad. In September 2011, catastrophic wildfire burned much of the Lost Pines, including almost all of Bastrop State Park. The wildfire, combined with a record drought, killed many of the trees in the Park.  As central Texas becomes warmer and drier, both fires and droughts will likely be more frequent and intense. Park management goals include restoration to diverse pine savanna, thought to have existed in the area prior to its logging a century ago, and continuing to provide habitat for the endangered Houston toad. We are investigating the ways in which post-fire plant communities are affected by (1) wildfire severity and (2) post-wildfire management actions, including hydromulch reseeding with sterile grasses for erosion control. Twenty-five 12-year-old permanent plots established using FIREMON protocols were re-surveyed in summer 2012 for woody and herbaceous species composition. 

Results/Conclusions

In most of our plots, pre-wildfire yaupon (Ilex vomitoria) abundance and pine needle drape resulted in heavy burn severity in 2011. In summer 2012, loblolly regeneration was greatest in plots that were scorched to moderately burned, had been treated with pre-wildfire prescribed burns, or both. The absence of loblolly seedlings in heavily burned plots may have been due to seed shortage, unsuitable seed beds, or both. Unburned plots appeared to be too shady for loblolly seedlings. Heavy hydromulching, which coated the ground and included a mix of sterile grass seed (× Triticosecale and Leptochloa dubia), suppressed loblolly regeneration. There was a statistically significant interaction between wildfire severity and hydromulch treatment on sand post oak resprout numbers. In unmulched plots there were more oak resprouts in lightly burned plots; in heavily mulched plots there were more oak resprouts in heavily burned plots. No statistically significant relationship was found between yaupon abundance or herbaceous species richness and hydromulch treatment or wildfire severity. Post-wildfire trajectories are likely to be determined by the ‘race’ between oak resprout and loblolly seedling regeneration. If initial trends continue, hydromulching may have controlled erosion at the cost of favoring oaks over pines.