Oil palm is the most productive vegetable oil crop per unit area and is crucial to the economy of developing countries such as Malaysia and Indonesia. However, it is also highly controversial due to the impact it has on biodiversity. Inputs of herbicides to control understory vegetation in plantations are high, which is likely to harm native biodiversity, but may be unnecessary in protecting oil palm yield. In this study we investigate the effects of understory manipulation using herbicides on soil fauna, litter decomposition rates, and soil abiotic variables: pH, soil organic carbon, soil water content, nitrogen, carbon/nitrogen ratio, potassium, and phosphorous. Understory vegetation was manipulated in three treatments: enhanced understory complexity (no herbicides, developed understory), normal understory complexity (intermediate herbicide use with some manual removal) and reduced understory complexity (heavy herbicide use, no understory vegetation). Two years after treatment, soil macrofauna diversity was higher in the enhanced than the normal, and reduced understory treatment. Furthermore, both macrofauna abundance and litter decomposition was higher in the enhanced than the reduced understory treatment. By contrast, soil fertility did not change between treatments, perhaps indicating there is little competition between oil palms, and understory vegetation. The reduction of herbicide use should be encouraged in oil palm plantations, this will not only reduce plantation costs, but improve soil biodiversity, and ecosystem functioning.

No abstract

Oil palm plantations have expanded rapidly in recent decades, and are causing substantial impacts on tropical habitats and biodiversity. However, owing to its long lifespan (25-30 years), oil palm forms a much more varied and structurally-complex habitat than many other crops. This can include abundant understory vegetation and also epiphytes on palm trunks. However, the diversity of this plantation vegetation has been poorly studied, and there has been little consideration of the impacts of common plantation vegetation management practices on plant communities. We conducted a long-term vegetation management experiment that forms part of the Biodiversity and Ecosystem Function in Tropical Agriculture (BEFTA) Programme in Riau, Indonesia. We manipulated herbicide and manual cutting regimes within mature oil palm plantations to create three different understory complexity treatments (Reduced, Normal, and Enhanced vegetation) across replicated sets of plots. Plant communities were surveyed before and after experimental understory vegetation treatments began in three different microhabitats: within the middle of the plantation block (core), on the road edge (edge) and on oil palm trunks (trunk). Part of the sampling was also conducted during a drought event. We recorded 120 plant species, which comprised a mixture of native, non-native, "beneficial," and "problem" species. We found substantial variation in plant communities between edge, core, and trunk microhabitats, indicating high levels of heterogeneity within the plantation. There were significant effects of varying understory treatment within both core and edge microhabitats, but no spillover of impacts into the trunk microhabitat. We also observed substantial impacts of drought on plant communities, with declines in either biomass, percentage cover, or richness seen across core, edge, and trunk microhabitats during low-rainfall periods. Our findings highlight the diversity of plant communities that can be supported within oil palm plantations, and the substantial impacts that management decisions, and also drought, can have on them. Given the Luke et al. Plant Communities in Oil Palm Plantations role that diverse plant communities can have in supporting species in other groups, this is likely to have a significant impact on the wider plantation biodiversity. We suggest that plantation management strategies give greater consideration to within-plantation understory plant communities and choose more wildlife-friendly options where possible.

Conversion of forest to oil palm plantations results in a significant loss of biodiversity. Despite this, first‐cycle oil palm plantations can sustain relatively high biodiversity compared to other crops. However, the long‐term effects of oil palm agriculture on flora and fauna are unknown. Oil palm has a 25‐year commercial lifespan before it must be replanted, due to reduced productivity and difficulty of harvesting. Loss of the complex vegetation structure of oil palm plantations during the replanting process will likely have impacts on the ecosystem at a local and landscape scale. However, the effect of replanting on biodiversity is poorly understood. Here, we investigate the effects of replanting oil palm on soil macrofauna communities. We assessed ordinal richness, abundance, and community composition of soil macrofauna in first‐ (25‐ to 27‐year‐old) and second‐cycle oil palm (freshly cleared, 1‐year‐old, 3‐year‐old, and 7‐year‐old mature). Macrofauna abundance and richness drastically declined immediately after replanting. Macrofauna richness showed some recovery 7 years after replanting, but was still 19% lower than first‐cycle oil palm. Macrofauna abundance recovered to similar levels to that of first‐cycle oil palm plantations, 1 year after replanting. This was mainly due to high ant abundance, possibly due to the increased understory vegetation as herbicides are not used at this age. However, there were subsequent declines in macrofauna abundance 3 and 7 years after replanting, resulting in a 59% drop in macrofauna abundance compared to first‐cycle levels. Furthermore, soil macrofauna community composition in all ages of second‐cycle oil palm was different to first‐cycle plantations, with decomposers suffering particular declines. After considerable biodiversity loss due to forest conversion for oil palm, belowground invertebrate communities suffer a second wave of biodiversity loss due to replanting. This is likely to have serious implications for soil invertebrate diversity and agricultural sustainability in oil palm landscapes, due to the vital ecosystem functions that soil macrofauna provide.

The expansion of oil palm (Elaeis guineensis) plantations is a primary cause of land-use change and biodiversity loss in Southeast Asia. This has led to an increasing demand for the development of more sustainable agricultural management practices in plantations, such as Integrated Pest Management. Although populations of carnivorous mammals show declines when forest is converted to oil palm, some species, such as Leopard Cats (Prionailurus bengalensis) have been found to persist. They are often encouraged by plantation managers for their conservation value, and as agents of pest control to manage rat populations. Despite this, little is known about whether they reduce pest rat numbers, or whether plantation management affects how they use the oil palm habitat. This study was based at the Biodiversity and Ecosystem Function in Tropical Agriculture (BEFTA) Programme in mature oil palm plantations in Riau, Sumatra, where there are three management strategies altering understory vegetation structure. We quantified Leopard Cat activity, invasive rat abundance and rat damage using camera traps, live traps, and visual estimates, respectively. We collected data over a 4-year period, before and after the management strategies were applied. We recorded three species of wild mammals (Leopard Cats, Common Palm Civets, and Wild Pig) within the plantations, of which Leopard Cats made up 82% of the total number of observations. We found that Leopard Cat habitat use was higher with increased understory vegetation, but that there was no effect of the vegetation treatments on rat abundance or rat damage. There was also a trend for reduced rat abundance with increased Leopard Cat activity. These results show that management practices can significantly affect Leopard Cat habitat use, with potential benefits for pest control. They also highlight the value of large-scale long-term manipulative experiments for developing more sustainable management practices in oil palm.