Abstract
Tropical biodiversity is threatened by the expansion of oil-palm plantations. Reduced-impact farming systems such as agroforests, have been proposed to increase biodiversity and ecosystem functioning. In regions where oil-palm plantations already dominate the landscape, this increase can only be achieved through systematic ecological restoration. However, our knowledge about the underlying ecological and socio-economic processes, constraints, and trade-offs of ecological restoration in oil-palm landscapes is very limited. To bridge this gap, we established a long-term biodiversity enrichment experiment. We established experimental tree islands in a conventional oil-palm plantation and systematically varied plot size, tree diversity, and tree species composition. Here, we describe the rationale and the design of the experiment, the ecosystem variables (soil, topography, canopy openness) and biotic characteristics (associated vegetation, invertebrates, birds) of the experimental site prior to the establishment of the experiment, and initial experimental effects on the fauna. Already one year after establishment of the experiment, tree plantings had an overall positive effect on the bird and invertebrate communities at the plantation scale. The diversity and abundance of invertebrates was positively affected by the size of the tree islands. Based on these results, we expect a further increase of biodiversity and associated ecological functions in the future. The long-term interdisciplinary monitoring of ecosystem variables, flora, fauna, and socio-economic aspects will allow us to evaluate the suitability of tree islands as a restoration measure. Thereof, guidelines for ecologically improved and socio-economically viable restoration and management concepts could be developed.
Highlights
A major driver of the current biodiversity crisis in South-East Asia is the large-scale transformation of natural rainforest into simplified production systems such as oil palm (Fitzherbert et al, 2008; Immerzeel et al, 2014)
We found a significantly positive effect of plot size on the difference in diversity of LL family richness (p < 0.05) and the difference in abundance of herb layer (HL) invertebrates in year one compared to the baseline (p < 0.05) (Figure 6); Tree diversity, did not affect the difference in richness, abundance, and biomass of birds and invertebrates (p > 0.05) (Figure 7)
By experimentally investigating plot size and tree diversity – two key factors in a restoration context – EFForTS-biodiversity enrichment experiment (BEE) aims at shedding light on the ecological and socio-economic processes associated with ecological restoration of oil-palm landscapes
Summary
A major driver of the current biodiversity crisis in South-East Asia is the large-scale transformation of natural rainforest into simplified production systems such as oil palm (Fitzherbert et al, 2008; Immerzeel et al, 2014). Besides the importance of protecting tropical forests for biodiversity conservation, integrating biodiversity conservation into the management of existing large-scale oil-palm plantations seems imperative (Koh et al, 2009; Foster et al, 2011; Luskin and Potts, 2011; Teuscher et al, 2015). Institutions like the Roundtable for Sustainable Palm Oil (RSPO) focus on non-deforestation policy, conservation of large expanses of high valuable habitat, and threatened species (RSPO, 2013). Restoring habitat heterogeneity at local and landscape scales might be an option to maintain or even enhance biodiversity in oil-palm landscapes (Azhar et al, 2011)
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