Oil palm plantations are expanding in tropical areas worldwide as demand increases. Although oil palms use less land than other oil crops, the conversion of tropical forest into oil palm plantations has had a devastating impact, threatening wildlife including orangutans, macaws, and spider monkeys.
It’s critically important that biodiversity and connectivity be integrated into these agricultural landscapes. Practices that support connectivity can be leveraged to benefit agricultural producers, where biodiversity provides ecosystem services to the benefit of wildlife and farmers alike.
Mateus, A.M.G., Domptail, S., Magiera, A. and Waldhardt, R. 2023. How landscape characteristics in a heterogeneous oil palm plantation mitigate pest abundance: A case study from Mapiripán, Colombia. Forest Ecology and Management 540: 121061.
A recent study in Colombia analyzed the relationship between landscape structure and oil palm pest abundance. Researchers classified landscape types on the Macondo oil palm plantation, which spans almost 6,000 ha and is 60% oil palm fields and 40% riparian forest, grassland, wetlands, roads, and buffer vegetation.
They calculated landscape metrics for these areas (including proximity, edge, edge density, diversity, and evenness) and used those metrics to run a cluster analysis. The analysis classified nine landscape structure types present on the plantation. Abundance data for two main oil palm pests, butterfly larvae of the split-banded owlet (Opsiphanes cassina) and red weevil (Rhynchophorus palmarum) were collected by larvae counts and bait traps over three years.
Two gradients emerged as the dominant descriptors of the plantation’s landscape characteristics: heterogeneity (diversity and complexity of vegetation) and connectivity (measured with proximity and edge indices). These features had a strong relationship with the abundance of insect pests. Well connected, heterogeneous landscapes had lower pest abundance overall. Homogenous landscape structure types had increased populations of red weevils. Interestingly, butterfly larvae were especially present in homogenous, low-vegetation areas where grassland patches were well connected to each other.
This result raises the concern that, in some cases, connectivity may support the movement of pests along with the movement of wildlife. Overall, the researchers advocate for complex landscape structure across the entire plantation in order to improve connectivity for wildlife in the surrounding forest and reduce pest abundance.
Though the study did not address the mechanisms by which pest abundance was reduced in diverse, connected landscapes, other research has established how corridors and complex landscapes can provide habitat for beneficial predators and balance ecosystem processes. The study goes on to say that connected forest patches within the plantation can create a spillover effect, allowing pest predators to enter the plantation, although this idea is contested.
The authors suggest that a complex, multi-functional agricultural landscape with high heterogeneity and connectivity can both support biodiversity and provide economic benefits. The authors emphasize the importance of using land-sharing and land-sparing techniques simultaneously— setting some land aside from human use for conservation, and integrating conservation practices on land that is being used.
While fully protected areas play a vital role, the biodiversity crisis and climate change demand all hands-on-deck— and all lands-on-deck— to mitigate ecological harm. Palm oil is here to stay, so management practices that prioritize landscape diversity and connectivity can play an important role in moving towards a more resilient and sustainable food system.
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