Over-hunting causes reduction in tree diversity over time

These are the results of a long-term study that also support the findings of Beaune et al (2013), reported here (Blog post: Elephant-dispersed trees suffer population declines when elephants are hunted out): when animals are removed from the ecosystem, drastic changes to forest composition soon follow (Harrison et al., 2013). In an impressive long-term experiment carried out in a 52 hectare plot in Borneo, Harrison’s team tracked the performance of over 470,000 trees of more than 1,100 species for a 15-year period, from the onset of intensive hunting. During that time the site lost nearly all its animals larger than 1 kg.  They found that while the density of saplings increased by over 25 per cent (because animals were no longer present to browse saplings), overall species diversity fell. Furthermore, there was a relative decline in animal-dispersed species compared to gravity or wind -dispersed species. Animal-dispersed species were also more clustered than they were prior to hunting. This study shows how catastrophic defaunation is for the composition and structure of a rainforest, and similar changes will almost certainly be seen in Gabon’s over-hunted forests over time.

Harrison RD, Tan S, Plotkin JB, Slik F, Detto M, Brenes T, Itoh A, Davies SJ, Consequences of defaunation for a tropical tree community. Ecology Letters 16:687-694.