The role of biodiversity in Southeast Asian tropical forest restoration

Thesis

Tropical forests in Sabah, Malaysian Borneo, are threatened by land use change and continued overexploitation. Active restoration of dipterocarp-dominated forests is used to increase the restoration value of these landscapes, and knowledge of the ecological mechanisms that promote tropical forest functioning is critical to realising this goal.

In this thesis, I use a long-term, field-scale experiment to investigate the effectiveness of active restoration techniques in a once-logged lowland dipterocarp forest. I show that enrichment planting of dipterocarp seedlings increases satellite-derived metrics of aboveground biomass, canopy cover, and leaf area index. I then show a clear relationship between ecosystem functioning and the biodiversity of enrichment planted seedlings. This relationship is likely driven by species-specific niche differences which generate stronger complementary effects through a more functionally diverse seedling cohort and is unlikely to be generated via stochastic processes as hypothesised under neutral theory.

At the local scale, I demonstrate that the survival of enrichment planted seedlings in a selectively logged forest may benefit from increasing densities of the surrounding tree matrix as a result of potential positive density-dependence. I also add to the evidence base that light is a primary driver of growth and survival within selectively logged dipterocarp forests. More data concerning the seedling environment, including microclimate variation, will help to provide a more comprehensive assessment of logged forest dynamics.

Finally, I show that survival and growth of enrichment planted seedlings are similar for most investigated species across an old-growth and secondary forest, demonstrating the capacity for old-growth forests to provide restoration target information from which to compare active restoration success. I also identify a growth-survival trade-off in both primary and secondary forests and demonstrate that my studied selectively logged dipterocarp forest is in an early successional stage and has not experienced a collapse in seedling growth and recruitment. However, I call for more work to understand the variables underlying species-specific responses to habitat perturbation.

This thesis helps to inform future restoration design, implementation, and monitoring across Sabah. To maximise the benefits of forest restoration to climate security, economic growth, and social wellbeing, a data-driven approach to forest restoration projects that utilises current ecological theory will become increasingly important.

Authors: Veryard, R

• DOI: 10.5287/ora-dxo8mpvad
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: enrichment planting; dipterocarpaceae; Sabah; remote sensing; Malaysia; restoration
• Subjects: Rain forest ecology; Remote sensing