Tropical forests support over two-thirds of the world's terrestrial biodiversity. However, between 35% and 50% of tropical forests have already been degraded, and the rate of deforestation continues to increase. Secondary forests, plantations and other human-modified habitats now dominate tropical landscapes, leading to concerns that human degradation of these landscapes will elevate greenhouse gas emissions and jeopardise ecosystem services at local, regional and global scales. The area of protected forests is unlikely to increase greatly in the future, so the persistence of tropical biodiversity and the important biogeochemical cycles and ecosystem services associated with it will depend to a large extent on the way we treat the wider tropical landscape. The Human Modified Tropical Forests programme seeks to 'significantly improve our understanding of the links between biodiversity and biogeochemical cycles in tropical forests' through 'integrated observations and modelling linked to gradients in forest modification'. To contribute towards this goal our consortium will use surveys along a modification gradient within the SAFE landscape in Sabah (Malaysian Borneo) to detect patterns, combined with manipulative field experiments to gain a mechanistic understanding of biodiversity-function linkages. We will assess links between above- and belowground components of tropical biodiversity and investigate the extent to which different elements of biodiversity (e.g. species of conservation concern) are associated with measures of ecosystem function (decomposition processes and biogeochemical cycles). We will then upscale from the experimental sites to the landscape-scale to generate spatial layers of ecosystem function, biodiversity, and greenhouse gas fluxes to inform policy scenario modeling. Our work will thus (1) characterise soil microbial function and measuring associated biogeochemical fluxes; (2) Experimentally test the links between aboveground biodiversity and soil function; (3) Build and add to existing datasets for bird and mammals, and explore correlations between ecosystem functioning and the distribution of species of conservation concern; and (4) Explore policy scenarios for optimising biodiversity and function protection.

Anthropogenic disturbance and land-use change in the tropics is leading to irrevocable changes in biodiversity and substantial shifts in ecosystem biogeochemistry. Yet, we still have a poor understanding of how human-driven changes in biodiversity feed back to alter biogeochemical processes. This knowledge gap substantially restricts our ability to model and predict the response of tropical ecosystems to current and future environmental change. There are a number of critical challenges to our understanding of how changes in biodiversity may alter ecosystem processes in the tropics; namely: (i) how the high taxonomic diversity of the tropics is linked to ecosystem functioning, (ii) how changes in the interactions among trophic levels and taxonomic groups following disturbance impacts upon functional diversity and biogeochemistry, and (iii) how plot-level measurements can be used to scale to whole landscapes. We have formed a consortium to address these critical challenges to launch a large-scale, replicated, and fully integrated study that brings together a multi-disciplinary team with the skills and expertise to study the necessary taxonomic and trophic groups, different biogeochemical processes, and the complex interactions amongst them. To understand and quantify the effects of land-use change on the activity of focal biodiversity groups and how this impacts biogeochemistry, we will: (i) analyse pre-existing data on distributions of focal biodiversity groups; (ii) sample the landscape-scale treatments at the Stability of Altered Forest Ecosystems (SAFE) Project site (treatments include forest degradation, fragmentation, oil palm conversion) and key auxiliary sites (Maliau Basin - old growth on infertile soils, Lambir Hills - old growth on fertile soils, Sabah Biodiversity Experiment - rehabilitated forest, INFAPRO-FACE - rehabilitated forest); and (iii) implement new experiments that manipulate key components of biodiversity and pathways of belowground carbon flux. The manipulations will focus on trees and lianas, mycorrhizal fungi, termites and ants, because these organisms are the likely agents of change for biogeochemical cycling in human-modified tropical forests. We will use a combination of cutting-edge techniques to test how these target groups of organisms interact each other to affect biogeochemical cycling. We will additionally collate and analyse archived data on other taxa, including vertebrates of conservation concern. The key unifying concept is the recognition that so-called 'functional traits' play a key role in linking taxonomic diversity to ecosystem function. We will focus on identifying key functional traits associated with plants, and how they vary in abundance along the disturbance gradient at SAFE. In particular, we propose that leaf functional traits (e.g. physical and chemical recalcitrance, nitrogen content, etc.) play a pivotal role in determining key ecosystem processes and also strongly influence atmospheric composition. Critically, cutting-edge airborne remote sensing techniques suggest it is possible to map leaf functional traits, chemistry and physiology at landscape-scales, and so we will use these novel airborne methods to quantify landscape-scale patterns of forest degradation, canopy structure, biogeochemical cycling and tree distributions. Process-based mathematical models will then be linked to the remote sensing imagery and ground-based measurements of functional diversity and biogeochemical cycling to upscale our findings over disturbance gradients.