Data from: Tree performance in a biodiversity enrichment experiment in an oil palm landscape

1. Large-scale conversion of tropical forests into oil palm monocultures
has led to dramatic losses of biodiversity and ecosystem functions. While
ecological restoration is urgently needed in many oil palm landscapes,
there is a lack of scientific knowledge of sustainable management
strategies. 2. We established experimental tree islands of varying sizes
(25 m2 to 1600 m2) and diversity levels (1, 2, 3 and 6 species) in an oil
palm plantation in Sumatra, Indonesia. Six native multi-purpose tree
species including Jengkol (Archidendron pauciflorum), Durian (Durio
zibethinus), Petai (Parkia speciosa), Meranti (Shorea leprosula), Sungkai
(Peronema canescens), and Jelutung (Dyera polyphylla) were planted between
living and felled oil palms. Here, we analyze the controlling factors of
tree growth and survival during the first four years at the level of local
neighborhood and tree island. 3. We found a significant effect of
diversity levels on tree productivity, i.e. basal area was higher in
mixed-species than in single-species tree islands. This overyielding was
attributed to enhanced tree growth, while mortality had no effect. In the
local neighborhood, tree species richness had a positive effect on tree
growth during the first year only, indicating that selection and dominance
of well-performing species at high level of diversity are most likely
driving overyielding. 4. Trees grew better away from living oil palms,
suggesting tree-palm competition. Proximity to felled oil palms increased
growth especially during the first years, during which the planted trees
might have benefited from the additional available space and resources.
Despite positive edge effects from the conventional oil palm management in
the surrounding, tree island size had an overall positive effect on tree
growth. 5. Synthesis and applications. We planted multiple native trees in
an oil palm plantation following a tree island pattern. The establishment
success differed widely among species. The selection of particular species
is a decisive factor to foster a positive relationship between diversity
andtree growth. Planting larger tree islands (e.g. 1’600 square meters) is
a better option to enhance tree growth, but tree-palm competition implies
a trade-off between tree growth and palm oil production locally.