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在不断变化，许多地区的木本植物生物量既有增加也有减少。发生这种情况的原因尚不清楚，但人们认为这既与当地土地利用(例如，采伐树木以获取能源和木材，使用火)有关，也与全球气候变化和二氧化碳浓度(有利于树木生长而不是草)有关。其结果是，根据稀树草原和干燥森林的类型以及人类使用的性质，变化模式会有很大的不同(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，数以亿计的农村和城市穷人使用这些稀树草原的产品来减轻贫穷的影响1。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，以非洲最近的工作为基础(参考文献2)。研究问题干燥热带地区木本植物生物量变化的模式和速率是什么？[用雷达遥感回答]我们能解开干燥热带木本植物生物量变化的驱动因素吗？[野外数据空间分析解答]方法论本博士学位将生态野外工作与雷达遥感和空间分析相结合。木本植物生物量的变化将使用最先进的雷达遥感绘制地图，并利用整个干燥热带地区的实地数据进行校准(方法2)。为了了解观察到的变化的原因，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模式之间的关系。来自长期地块的数据3，记录树木种群和植物区系组成如何变化，将被用来补充空间分析，因为这些生态信息可以“确定”变化的原因。这将涉及在干旱的热带地区的几个地点收集新的数据，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.