Framework of this study:
This research agenda will be realized in the framework of the established large-scale, long-term experiment within mono-cultural palm oil plantations. On each plot, enrichment plantings of varying plot sizes are established. Across experimental plots, the size varies adopting a random partitions design (Bell et al. 2009) with four partitions series (plot sizes of 5x5, 10x10, 20x20 and 40x40 m) and one plus control plots without planting and with oil palm) resulting in a total of 52 experimental plots in PT Humusindo. Among these plots, species diversity levels varies additionally: 1, 2, 3 and 6 tree species.
The tree species include three fruit trees (Parkia speciosa, Fabaceae; Archidendron pauciflorum, Fabaceae; Durio zibethinus, Malvaceae) and three other native species (Dyera costulata, Apocynaceae; Peronema canescens, Verbenaceae; Shorea leprosula, Dipterocarpaceae). The fruit trees are used by humans and animals, and the native trees are sources for natural latex and timber. The two Fabaceae may enhance the nitrogen availability by nitrogen fixation. The multiple uses of the tree species may positively influence the further acceptance of such a planting scheme by oil palm growers. This specific set of trees was chosen based on availability in local Indonesian nurseries and reproductive conditions in 2010. They represent an initial set of tree species for the experiment while their identity may change if the availability or reproductive conditions change prior to the experiment.
Research in the first stage of the experiment will, additionally to seed rain and successional dynamics of understory plant communities (realized by Anne Gérard), focus on determinants of growth and survival in the planted trees. After the initial planting of the trees, the survival success of individual trees and of tree species will be monitored and analyzed by Anne Gérard. As proxies for growth and biomass increment, the tree height and the basal diameter (measured 10 cm above the ground; compare Potvin & Gotelli 2008) of each individual will be measured on an annual basis. Additionally, the canopy openness will be measured with hemispherical photographs.