Competition and yield in oil palm agroforestry: examining the ‘yield penalty’ of biodiversity

Natural rain forests have been transformed into large-scale mono-cultural oil palm plantations. This has led to dramatic losses in biodiversity and ecological functioning. To reduce the impact of such practices, farming systems have been suggested, such as agroforests. However, there is not enough knowledge to date concerning underlying ecological, as well as socio-economic processes, constraints and tradeoffs of such systems in oil palm plantations. To fill this gap of knowledge, the Collaborative Research Center 900 has created a long-term biodiversity enrichment experiment (EFForTS-BEE). Experimental tree-islands were established in a conventional oil-palm plantation. One of the main goal of the experiment is to assess ecological and socio-economic trade-offs of such agroforests. To quantify ecosystem services, especially reflected by oil palm yield, the drivers of oil palm yield in these agroforests need to be identified. This research project contributes to understanding the types of competition between trees and oil palms and their effects on oil palm productivity by investigating the effects of light competition. As part of ongoing research activities in EFForTS-BEE, yield of individual oil palms inside and outside the plots are monitored. First results indicate an increase in oil palm yield after thinning and establishing tree islands. Based on these findings, the project will investigate the role of light competition as a yield determining factor on the individual palm/tree level. Additionally, it will continue and extend the oil palm yield survey to determine if the initial yield increase can be maintained over time.

Hypotheses:

• H1: Oil palm yield is negatively correlated with height of neighboring trees.
• H2: Oil palm yield is negatively correlated with crown size of neighboring trees.
• H3: Observed trend of increased oil palm yield after thinning and intercropping with trees decreases over time.