In East Texas, excluding feral hogs from forest plots for 7 years more than doubled the abundance of woody plant species with large seeds

Feral hogs are known for rooting through forest floors in search of food, but their effects can extend beyond the soil they disturb. By eating seeds, trampling vegetation and altering ground cover, the animals can influence which plants survive to become the next generation of trees. According to a 2009 study published in Forest Ecology and Management, excluding feral hogs from forest plots in East Texas’s Big Thicket National Preserve for seven years increased the abundance of woody plants, particularly species with large seeds.

Seven years without hogs changed the understory

The research assessed the impacts of feral hogs on a pine-hardwood forest in the Big Thicket. They created 16 plots that were 10 metres by 10 metres and surrounded eight of them with fencing to exclude hogs from entering. The other eight were left without the fence so that they could compare them for seven years. They found that hog exclusion increased the diversity of woody vegetation in the forest understory. This effect was strongest in plant species with large seeds. Each species with a mean seed mass above 250 milligrams had more than twice as many individuals in the fenced plots as in the unfenced plots.


Among these trees are hickories (Carya), oaks (Quercus) and tupelos (Nyssa). Their seeds are consumed by hogs, and the study authors suggested that nut and seed consumption may help explain why these trees are rarer where hogs have access. Without hogs, more seeds could survive long enough to germinate and contribute to forest regeneration. That did not mean there were twice as many trees in the forest. There was this difference observed in the study plots, especially among large-seeded woody trees.

Rooting also altered the forest floor

In addition to eating seeds, hogs disturb soil and leaf litter by rooting for food, changing the conditions in which plants grow. In the Big Thicket experiment, plots accessible to hogs had more bare soil and less plant cover and surface litter than fenced plots. The soil carbon-to-nitrogen ratio was also lower in plots where hogs were present, possibly because their activity accelerated nitrogen mineralisation. A 2007 study published in Human-Wildlife Interactions examined three management units in Big Thicket National Preserve and found that rooting and wallowing had damaged an average of 28 per cent of the surveyed area. The extent varied by landscape, reaching 45 per cent in floodplains in the Big Sandy unit and 46 per cent in flatlands in the Turkey Creek unit.

Together, the findings show that feral hogs can affect forest vegetation in different ways. By eating seeds, they can limit the regeneration of native trees, particularly large-seeded species. At the same time, their rooting disturbs soil and ground cover, potentially creating conditions that favour some invasive plants. In a 2009 experiment, the invasive Chinese tallow tree (Sapium sebiferum) was more than twice as abundant in plots where hogs were present. The researchers suggested that soil disturbance might help explain this pattern, although the experiment did not establish the exact cause. The results indicate that hogs can hinder the recovery of some native plants while potentially favouring the spread of an invasive tree.

What the findings mean for forest management

Feral hogs are an established management concern in the Big Thicket. The National Park Service identifies them as a major non-native species in the preserve because of the habitat disturbance they cause and the difficulty of controlling their populations. The seven-year experiment provides evidence that excluding hogs can improve conditions for woody plant regeneration, especially for species whose large seeds are attractive to the animals. Such changes matter because the seedlings and saplings growing beneath the canopy help determine the composition of the forest in the future. However, the research was conducted in a specific forest environment using small-sized experimental patches. The findings do not show that fencing would revive all hog-affected forests or that all plant species would respond the same way.