Effects of native pigs (Sus scrofa) on woody understorey vegetation in a Malaysian lowland rain forest

Large mammals often play important roles in determining the structure and composition of plant communities. This study focused on the extent to which wild pigs (Sus scrofa) influence the dynamics of tree seedlings and saplings in a lowland rain forest at Pasoh Forest Reserve in West Malaysia. Native wild pigs are common in the study area and may significantly influence growth and survivorship of woody plants in the understorey through several activities - namely, nest building, soil rooting and seed predation. To test experimentally the impact of pigs on the plant community, eight 49-m² exclosures were constructed. After 2 y, the number of recruits inside exclosures was three times greater than in unfenced control plots. Stem density was highly correlated with species richness, which also increased significantly inside exclosures. Height growth of plants was greater in the exclosures by 52.5% for trees between 1 and 7 m tall. Trees less than 1 m tall, however, exhibited no differences in growth. Mortality of plants also did not differ between treatments. The observed differences between exclosure and control plots can be attributed to soil-rooting and seed predation, suggesting that these two behaviours of wild pigs are important to plant dynamics in the understorey.