Assessing the impact of feral hog populations on the natural resources of Big Thicket National Preserve

The Big Thicket National Preserve (BTNP) is a unit of the National Park Service whose mission prioritizes conservation of its wildlands in the United States. One threat to natural resources of the BTNP has been impacts associated with feral hog (Sus scrofa) activities. Population numbers of this non-native game species have increased throughout Texas, including areas within the preserve. Recreational hunting permitted by the BTNP has served as a means of controlling hog numbers, although the reported amounts of hog damage to park resources appear to have increased in recent years. Population reduction of feral hogs and mitigation of their impacts require research that documents and validates feral hog impacts on park resources. Here, I evaluated (1) population trends of feral hogs for the past 20 years via data from hunter-card surveys and track-counts, and (2) feral hog impacts on native vegetation for 3 management units of the BTNP. Results from my analysis suggest a nearly 3-fold increase in hog numbers throughout the preserve since 1981. The overall damage to vegetation from hog rooting or wallowing averaged to 28% among the 3 units of the BTNP. Landscape features such as topography, soil moisture, soil type, and dominant vegetative cover types were used to predict hog damage. Floodplains had the most damage in the Big Sandy unit (45%), while flatlands were mostly impacted in the Turkey Creek unit (46%), and uplands in the Lance Rosier unit (32%). Vegetative cover was an important variable in explaining variation in hog damage throughout the 3 units of the preserve. Impacts were more widespread across different vegetative strata than previously believed. Study results also support the premise that hog damage in the BTNP parallels the increase in hog abundance over the past 20 years. A more aggressive program for population reduction of feral hogs and mitigation of their impacts is recommended for the BTNP to continue to meet its legal mandates for conservation.