This is a timely article that underscores the urgent need for more research to assess the biodiversity impacts of oil palm agriculture.

Currently, more than a third of the palm oil produced in Malaysia and Indonesia is exported to China and India, mostly for use in the food processing industry. The energy market for palm oil is also growing because this crop is the most productive among current major biodiesel feedstocks. My research shows that by 2050, global biodiesel demand could lead to substantial expansion of oil palm agriculture (1.5-fold), which could in turn result in losses of up to 5.4 million ha of natural habitats in major oil palm-producing countries (Koh 2007).

In an effort to address the growing environmental concerns and to protect its share of the biofuel market, the Malaysian oil palm industry has argued both that oil palm plantations are beneficial to biodiversity (http://www.mpoc.org.my/ma...), and that expansion of oil palm cultivation has not come at the expense of forests (http://www.mpoc.org.my/en...). Recently, David Wilcove and I used national land-use data compiled by the Food and Agriculture Organization of the United Nations to investigate these claims (Koh & Wilcove 2008). Our study shows that between 55% and 59% of the total extent of oil palm expansion in Malaysia, and at least 56% of that in Indonesia likely had occurred at the expense of forests. We also show that the conversion of either old-growth or secondary forests to oil palm plantations results in significant biodiversity losses.

Turner et al.’s article also raised the question of whether it would be possible to enhance biodiversity in oil palm plantations. I recently conducted an empirical study in ~40,000 ha of oil palm plantations in Borneo to address this very question, focusing on approaches the oil palm growers currently employ. These approaches include the planting of flowering plants to attract the insect predators and parasitoids of oil palm pests. The results show that biodiversity in oil palm plantations could be marginally enhanced by altering vegetation characteristics at the local level (e.g., percent ground weed cover), or by increasing natural forest cover at the landscape level (Koh 2008a). However, I emphasize that the increase in biodiversity resulting from these practices is quite minor relative to the loss that occurs when forests are converted to oil palm.

Turner et al. also hinted that such biodiversity enhancements may bring financial rewards to oil palm growers. I also recently conducted a bird-exclusion experiment in Bornean oil palm plantations to test the hypothesis that insectivorous birds inhabiting plantations provide a natural pest control service for oil palm agriculture. The results show that bird exclusion significantly increased herbivory damage to oil palm seedlings compared to control treatments, and that the magnitude of this insect control increased with the abundance of insectivorous birds (Koh 2008b). These data strongly suggest that biodiversity-friendly plantations may benefit not only native species but also oil palm growers from the ecosystem service that these species provide.

I echo Turner et al.’s key argument that to gain a better understanding of the biodiversity impacts of oil palm agriculture, more studies must be conducted for different taxonomic groups and across oil palm-growing regions of the world. I hope scientists will engage non-governmental organizations, oil palm producers, local governments, and rural communities to come up with creative approaches to both protect the forests and biodiversity under threat from oil palm expansion and improve the livelihoods of the local people.

Lian Pin Koh
Department of Ecology and Evolutionary Biology, Princeton University, 106A Guyot Hall, Princeton, New Jersey 08544, USA (email: lkoh@princeton.edu)

References
Koh, LP (2007) Potential habitat and biodiversity losses from intensified biodiesel feedstock production. Conservation Biology 21: 1373-1375.
Koh, LP (2008a) Can oil palm plantations be made more hospitable for forest butterflies and birds? Journal of Applied Ecology (revised manuscript awaiting decision).
Koh, LP (2008b) Birds defend oil palms from herbivorous insects. Ecological Applications (in press).
Koh, LP, Wilcove, DS (2008) Is oil palm agriculture really destroying tropical biodiversity? Conservation Letters (in press).