The response of savannas and dry forests to global change: disentangling the effects of climate change, land use and changing CO2 using radar

Savannas and dry forests are in flux, with both increasing and decreasing woody biomass in many areas. Why this is happening is unknown, but it is thought to be linked to both local land-use (e.g. tree harvesting for energy and timber, the use of fire), and global changes in climate and CO2 concentration (which favours the growth of trees over grasses). The result is hugely variable patterns of change depending on the type of savanna and dry forest and the nature of human use (Fig 1). This matters because of the linkages between ecosystem services derived from these ecosystems and human livelihoods: for example, in southern Africa, hundreds of millions of the rural and urban poor, use products from these savannas to mitigate the effects of poverty1. This project aims to understand the patterns and causes of vegetation change across the entire dry tropics, building on recent work in Africa (ref2).

Research Questions
What are the patterns and rates of woody biomass change in the dry tropics? [to be answered with radar remote sensing]
Can we disentangle the drivers of woody biomass change in the dry tropics? [answered with field data + spatial analysis]
Methodology
This PhD will mix ecological fieldwork with radar remote sensing and spatial analysis. Changes in woody biomass will be mapped using state of the art radar remote sensing, calibrated with field data from across the dry tropics (method in2). To understand the causes of the observed changes, we will use spatial analysis and field data. The spatial analysis will analyse how change is related to the spatial patterns of climate change, land use and vegetation type. Data from long term plots3,recording how tree populations and floristic composition have changed will be used to complement the spatial analysis because this ecological information can "fingerprint" the causes of change. This will involve collecting new data at several sites across the dry tropics and working with partners to collate existing data.