Effects of Yaupon, Chinese privet, and Chinese tallow on understory fuel flammability in East Texas hardwood and pine ecosystems

Forest understory fuels can have profound effects on fire behavior and crown fire initiation. Accurate fire behavior prediction in understory fuels is an essential component for estimating fire intensity and severity during wildfire and prescribed fire events. This study focused on estimating temporal and seasonal changes in fuel loading and flammability parameters associated with the expansion of invasive yaupon (Ilex vomitoria), Chinese privet (Ligustrum sinense), and Chinese tallow ( Triadica sebifera) in East Texas pine and hardwood ecosystems. Fuel loading data of invasive species infested sites indicated significant increases in understory biomass when compared to1988 estimates, suggesting a clear need to revise regional fuel models. Multiple and simple regression biomass prediction equations were developed for all three invasive species to facilitate fuel load estimates. Oxygen bomb calorimetry (OBC) and thermogravimetric analysis (TGA) were used to identify potential seasonal variations in species-specific flammability indices. OBC and TGA proximate analysis indicated significant seasonal differences in mean net heat content (NHC), ash %, and volatile matter percent (VM %) in Chinese privet and tallow. Yaupon and Chinese privet exhibited the highest mean NHC values in both seasons. Comparison of thermokinetic analyses using mean activation energy (Ea), relative spontaneous ignition temperature (RSIT), and gas-phase combustion rate and duration revealed flammability differences among all species during growing and dormant seasons. Ea and RSIT results indicated that yaupon foliage and Chinese tallow wood were the most ignitable and combustible fuels in both seasons. Unique flammability results for Chinese tallow wood may warrant future testing of new integrated management approaches utilizing prescribed fire.