Land-use intensification and deforestation are affecting the potential of ecosystems to store carbon and maintain biogeochemical cycles. Tropical forest conversion is associated with severe losses in species and functional diversity, which may impair ecosystem resilience in response to disturbance and environmental stresses.
In Phases 1 and 2, subproject B04 Leuschner investigated (1) how biomass carbon pools and the carbon sequestration potential of the vegetation are affected by forest transformation, and (2) whether oil palm and rubber monocultures are more susceptible to water deficits and reduced functional diversity. We found that forest transformation to oil palm and rubber plantations reduced biomass carbon pools up to fourfold and decreased net carbon uptake potential. The comparative study of tree hydraulic properties showed that wood anatomy and embolism resistance are highly variable among rainforest tree species, which may buffer forest productivity against drought stress periods, while oil palm has a rather cavitation-sensitive xylem.
In Phase 3, B04 Leuschner/Kotowska will continue the wood growth measurements to generate a 10-yr time series, which will allow analysing inter-annual productivity fluctuations and carbon source-sink dynamics. In order to upscale results to the landscape level, we will measure plant aboveground biomass in the interdisciplinary Landscape Assessment. Further, we link biomass to plant structural and functional variables with the aim to parameterize landscape-scale productivity and biogeochemistry models. We can capitalize on the database of morphological and functional traits collected for several hundred woody species jointly with B06 Kreft, which will be completed by fine root traits from selected species with the aim to analyse leaf, wood and root economics spectra for different plant life forms and link them to phylogeny. Additionally, we will study belowground interactions between oil palms and planted tree islands in the B11 Oil Palm Biodiversity Enrichment Experiment (EFForTS-BEE) to improve the mechanistic understanding of palm-tree belowground competition. We attempt to quantify spatial segregation of water and mineral nitrogen uptake between palm and tree root systems using miniature sap flow gauges and 15N tracers, and explore fine root distribution and turnover in the contact zone. Resource consumption will be related to the growth performance to conclude on competition intensity and asymmetry between species.