The Effects of Wild Pigs (Sus scrofa) on Woody Understory Vegetation in Lowland Rain Forest of Malaysia

• Main Author: Ickes, Kalan Leonard
• Other Authors: Vernon Wright
• Format: Others
• Language: en
• Published: LSU 2001
• Subjects: Plant Biology (Biological Sciences)
• Online Access: http://etd.lsu.edu/docs/available/etd-1116101-083403/

An increasingly urgent task in the field of conservation biology is to identify changes in abiotic and biotic interactions that result when large areas of forest are converted to small fragments surrounded by anthropogenic landscapes. My research, conducted in lowland dipterocarp rain forest at the 2,500-ha Pasoh Forest Reserve in Peninsular Malaysia, investigated a novel but strongly negative edge effect - namely, a tremendous increase in the density of wild pigs (Sus scrofa) and the resulting deleterious impacts on the understory plant community. The absence of feline predators due to the small size of the reserve and the presence of a year-round food supply in the agricultural areas surrounding the reserve are believed to be the main factors contributing to increased pig density. Line transects were conducted to determine pig density within Pasoh. Density in 1996 and 1998 was estimated to be 47 and 27 pigs/km², respectively, or 10 100 times historical levels. Fences were constructed to exclude pigs from control plots to quantify the impact of soil rooting and seed predation on plants in the understory. After two years, plots inside exclosures had three times more recruits, greater species richness, and 53% more height growth among plants 1 7 m tall than did adjacent plots to which pigs had access. Surveys were conducted in 1995, 1996, and 1998 to determine the number of reproductive nests constructed by pigs. Pigs constructed an estimated 6.0 nests/ha/year during this time, with an average nest composed of 145 snapped saplings and 117 uprooted saplings. Nest building accounted for 28.9% of all mortality for trees 1 2 cm diameter at breast height. Uprooted stems died, but snapped stems produced a leafless stump that could resprout. Observations of >1,800 stumps for 36 months revealed large differences in resprouting among species, families, and groups of plants with similar life history characteristics. Overall, the results of the different studies suggest that if elevated pig densities continue there could be a shift away from the currently dominant Dipterocarpaceae and Euphorbiaceae.