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

热带稀树草原和干燥森林在不断变化，许多地区的木质生物量既有增加又有减少。发生这种情况的原因尚不清楚，但据认为与当地的土地使用（例如，树木收获能源和木材，使用火）以及气候和二氧化碳浓度的全球变化（有利于树木而不是草的生长）有关。其结果是巨大的变化模式取决于热带草原和干燥森林的类型和人类使用的性质（图1）。这一点很重要，因为这些生态系统所提供的生态系统服务与人类生计之间存在联系：例如，在南部非洲，数亿农村和城市穷人使用这些热带稀树草原的产品来减轻贫困的影响。该项目的目的是了解整个干旱热带地区植被变化的模式和原因，建立在最近的工作在非洲（参考文献2）。[to我们能解开干旱热带地区木本生物量变化的驱动因素吗？[回答与现场数据+空间分析]方法这个博士将生态实地考察与雷达遥感和空间分析相结合。将使用最先进的雷达遥感技术绘制木本生物量的变化图，并使用整个干旱热带地区的实地数据进行校准（方法2）。为了了解所观察到的变化的原因，我们将使用空间分析和实地数据。空间分析将分析变化如何与气候变化、土地利用和植被类型的空间格局相关联。记录树木种群和植物区系组成如何变化的长期图3的数据将用于补充空间分析，因为这种生态信息可以“指纹”变化的原因。这将涉及在干旱热带地区的几个地点收集新数据，并与合作伙伴合作整理现有数据。

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 QuestionsWhat 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]MethodologyThis 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.