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Abstract

Clearing forests for oil palm plantations is a major threat to tropical terrestrial biodiversity, and may potentially have large impacts on downstream marine ecosystems (e.g., coral reefs). However, little is known about the impacts of runoff from oil palm plantations, so it is not clear how oil palm development should be modified to minimize the risk of degrading marine ecosystems, or how marine conservation plans should be modified to account for the impacts of oil palm development. We coupled terrestrial and marine biophysical models to simulate changes in sediment/nutrient composition on reefs as a result of oil palm development in Papua New Guinea, and predicted the response of coral and seagrass ecosystems to different land-use scenarios. The condition of almost 60% of coastal ecosystems were predicted to be substantially degraded (more than a 50% decline from their initial state) after 5 years if all suitable land was converted to oil palm, with only 4% of coastal ecosystems improving in condition as trees matured. We evaluated marine ecosystem condition if the oil palm developments were consistent with global sustainability guidelines and found that there were only slight improvements in ecosystems condition compared to the scenario with complete conversion of forest to oil palm. Substantially reducing the impact of oil palm development on marine ecosystems required limiting new plantings to hill slopes below 15°, a more stringent restriction than currently allowed for in the sustainability guidelines. We evaluated priority marine conservation areas given current land-use and found reef ecosystems in these areas will likely be heavily degraded in the future from runoff. We find that marine conservation plans should be modified to prioritize turbid areas where coral communities may be more tolerant of increased suspended sediment in the water. The approach developed here provides guidelines for modifying marine conservation priorities in areas with oil palm development. Importantly, oil palm development guidelines cannot be truly ecologically sustainable unless they are modified to account for the impacts of oil palm on coastal marine ecosystems.

5. Conclusion

Our proposed “best practices” guidelines – no development N15° slope - should be considered for future oil palm expansion in the tropics. We illustrate the potential differences in soil erosion, runoff, and associated diffuse impacts on reef condition for agricultural practices that do not follow sustainability guidelines versus those that do. Sustainable oil palm development will reduce the impacts of pollutants on marine ecosystems, but more stringent restrictions on development are required to reduce coral degradation. Ideally, oil palm expansion must consider marine and terrestrial resource needs and inter-system connections. We recommend guidelines for sustainable oil palm development be expanded to explicitly account for ocean impacts. Finally, for decision-makers planning marine conservation at the land-sea interface, reserves designed with only existing land-uses in mind may be inadequate, and consideration of future land-use change impacts must be considered to avoid loss of marine ecosystems