Study shows oil palm plantations impact amphibians
KINABATANGAN: Recent research published in Biological Conservation by scientists at Danau Girang Field Centre, Cardiff University and the University of Melbourne have found that oil palm plantations, which produce vegetable oil used in foods, cosmetics and cleaning products, may negatively affect amphibians in nearby areas of rainforest.
The study was conducted in Sabah, and highlights the importance of maintaining areas of natural forest habitat in order to preserve existing biodiversity.
Across Southeast Asia, large areas of existing rainforest have been replaced with large scale oil palm plantations, which has resulted in detrimental impacts on forest species. Agricultural plantations, such as oil palm, not only support fewer species compared to rainforest habitats, but they are also thought to negatively impact species in adjacent areas of natural habitat due to ‘edge effects’.
Edge effects are changes in community dynamics or species diversity that occur at habitat boundaries, and such effects can be pronounced if habitat structure changes abruptly between two different habitat types.
Until recently, there was little information surrounding the effects of oil palm plantations on amphibian communities in adjacent forest habitats.
The team, primarily based at Cardiff University and at the Danau Girang Field Centre located within the Kinabatangan Wildlife Sanctuary in Sabah, examined the number of frog species found in forest and plantation habitats, and assessed whether community composition changed across these habitat types.
They also evaluated whether both the number of frog species and their community composition varied in relation to environmental parameters including distance to the forest-plantation interface, standing surface water and canopy density.
Dr Sarah Scriven, now a post-doctoral research associate at the University of York, and joint first author of the research paper, said: “It is really important to widen our understanding of how oil palm agriculture may impact forest taxa that are sensitive to disturbance, and amphibians are especially vulnerable to habitat disturbance due to a complex number of factors relating to their specific physiology and ecology”.
“To determine the effects of oil palm agriculture on frog communities, we conducted nocturnal visual encounter surveys over a six-month period in both plantation and forest habitats at different distances from the forest-plantation interface. During these surveys we visually searched for both terrestrial and arboreal frog species and listened out for their specific calls,” she added.
The study showed that forest sites supported a higher number of frog species compared to oil palm plantation sites, and that plantations were dominated by wide-ranging, terrestrial species of little conservation concern. Forest habitats, however, supported both more endemic species (i.e., species found only in Borneo) and more arboreal species compared to plantation habitats.
Dr Graeme Gillespie, a wildlife ecologist based at the Department of Environment and Natural Resources in Northern Territory, Australia, said: “We found that the number of frog species declined as proximity to the forest-plantation interface increased, and our results suggest for the first time that oil palm plantations have adverse negative impacts on amphibian diversity several kilometres into adjacent forest habitats”.
The researchers also said that the change in habitat structure following conversion of rainforest to oil palm plantations is likely responsible for the changes in frog species richness and community composition. In particular, the findings of the study show that frog species richness increased with canopy density, which also increased with distance from the forest-plantation interface. The results therefore suggest that a higher number of frog species were found in less disturbed forest sites far from the forest-plantation edge.
Dr Benoit Goossens, director of Danau Girang Field Centre, Reader at Cardiff University and an advisor to the Sabah Wildlife Department, said: “Whilst oil palm provides a valuable and economically important crop, this study demonstrates that oil palm plantations may have detrimental effects on sensitive taxa in adjacent rainforest habitats”.
Benoit also pointed out that these new findings suggest that in order for small forest patches or narrow corridors to be of long-term conservation value in oil palm landscapes, their sizes and widths need to adequately account for the considerable influence of edge effects.
The research paper, ‘Edge effects of oil palm plantations on tropical anuran communities in Borneo’ can be found online at: https://wwwsciencedirect-com.abc.cardiff.ac.uk/science/article/pii/S0006320717306377