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

稀树草原和干燥森林处于不断变化之中，许多地区的木质生物量有增加也有减少。发生这种情况的原因尚不清楚，但人们认为这与当地土地利用（例如，为了获取能源和木材而砍伐树木，使用火）、全球气候变化和二氧化碳浓度（这有利于树木而不是草的生长）有关。其结果是，根据稀树草原和干林的类型以及人类使用的性质，变化模式变化很大（图1）。这一点很重要，因为来自这些生态系统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，数亿农村和城市贫困人口使用来自这些稀树大草原的产品来减轻贫困的影响。该项目旨在了解整个干旱热带地区植被变化的模式和原因，以最近在非洲开展的工作为基础（参考文献2）。研究问题：干燥热带地区木质生物量变化的模式和速率是什么？[用雷达遥感回答]我们能解开干旱热带地区木质生物量变化的驱动因素吗？这个博士将把生态实地调查与雷达遥感和空间分析结合起来。木质生物量的变化将使用最先进的雷达遥感绘制，并使用来自整个干燥热带地区的实地数据进行校准（方法2）。为了了解观测到的变化的原因，我们将使用空间分析和现场数据。空间分析将分析变化与气候变化、土地利用和植被类型的空间格局之间的关系。记录树木种群和植物区系组成变化的长期标绘数据将用于补充空间分析，因为这些生态信息可以“指纹”显示变化的原因。这将涉及在干旱热带地区的几个地点收集新数据，并与合作伙伴一起整理现有数据。

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.