Assessing the impacts of the 2010 drought on Amazon zone of transition

2010年，亚马逊流域经历了不寻常的干旱，这是五年来的第二次大干旱，这种模式与该地区未来气候的一些预测非常相似。这是因为大多数气候模型预测，由于全球气候变化，下个世纪的旱季强度会增加，气温也会升高。无论长期气候变化是否已经涉及到当前的事件，都可以帮助我们评估潮湿的森林、落叶林和稀树草原生态系统和物种对干燥的反应，从而帮助评估亚马逊气候干燥时的潜在影响规模。我们的团队在该地区拥有一个庞大的实地样本网络，由于这些样本是标准化的，它们代表了衡量干旱实际影响的绝佳机会。我们已经在2005年的严重干旱中做到了这一点（当时被称为“世纪干旱”，但今年的程度超过了这一点）。在这个方案中，我们将重点放在亚马逊南部边缘的场地上，该地区受到2010年干旱的严重影响。这一大片区域是亚马逊潮湿森林物种、落叶物种和稀树草原之间的“紧张地带”，不同的植被类型有时在同一地点相邻。在这里，我们有30个可用的永久地块，因此我们能够首次测量在这个森林/稀树草原混合带对不同物种和植被形成的实地影响。这一点很重要，因为预计在这些生态紧张的区域内，长期的植被变化将首先被观察到，这些高多样性和高碳储量的区域可能会显著影响区域碳排放。我们计划做以下工作：1)最近调查30个亚马逊南部样地，记录树木生长和植被生产力。2)重新测量近500棵树，我们在干旱前测量了它们的结构细节，以评估干旱是否改变了它们。3)在关键树种的树上安装高精度测量工具（“树径计”），以便更好地监测未来的干旱。4)分析从(1)和(2)收集的数据，以检验我们的假设：2010年的干旱导致了森林而非稀树草原的生物质碳损失。我们预计稀树草原将比森林更有弹性，森林的反应将与2005年的情况相似。2010年的干旱加速了树木的死亡，减少了森林的生长，但稀树草原却没有。我们预计森林物种在面对同样程度的干燥时比稀树草原物种更敏感。生物量损失和/或死亡率最大的森林和稀树草原样地是土壤最浅的样地。我们预计土壤深度会影响干旱反应，较浅的土壤具有较少的水分储备。在每个林分中，生长在干旱地区的物种比生长在干旱地区的物种更具抗旱性。我们认为，树木面临的干旱风险与其地理分布有关，因此，通常在潮湿气候中发现的物种将比它们的邻居对干旱更敏感。物种干旱敏感性的差异与结构性状的差异有关。我们预计更耐旱的常绿树木将有一个更保守的水力结构，如致密的木材。本研究的预期成果是：1)改进了亚马逊过渡森林对干旱敏感性的量化。2)首次评价了森林和稀树草原树木对干旱条件的差异敏感性。3)通过整合(1)(2)，可以更好地理解热带稀树草原在“紧张地带”取代森林的可能性，甚至在气候干燥时成为亚马逊核心森林的可能性。4)提高对抗旱生理基础和土壤条件重要性的认识。5)为当地合作者评估未来干旱的影响而安装的基础设施。

In 2010 the Amazon Basin experienced unusually dry conditions, a second major drought in 5 years, a pattern which is remarkably similar to some predictions of the future climate of the region. This is because most climate models predict an increase in dry season intensity, and all an increase in temperature in the coming century as a consequence of global climate change. Whether or not long-term climate change is already involved the current event can help us evaluate how humid forest, deciduous forests and savanna ecosystems and species respond to drying, so helping assess the potential scale of impacts as the Amazon climate dries. Our team has a large network of on-the-ground sample plots in the region, and because these are standardised they represent an excellent opportunity to measure the actual impacts of drought. We already did this with the severe 2005 drought (described then as 'the drought of the century' but surpassed in extent this year). In this proposal we focus on our sites at the southern fringes of Amazonia, an area very strongly affected by the 2010 drought.This large area is a 'zone of tension' between Amazon moist forest species, deciduous species, and savanna, with the various vegetation types sometimes adjacent in the same sites. Here we have 30 permanent plots available so we are able for the first time to measure the on-the-ground impacts on different species and vegetation formations at this forest/savanna mixing zone. This is important because it is expected that within these zones of ecological tension that long-term vegetation changes will first be observed, and these areas of high diversity and high carbon storage could significantly affect regional carbon emissions.We plan to do the following:1) Recensus 30 southern Amazon plots to record tree growth and vegetation productivity.2) Remeasure nearly 500 trees where we have pre-drought measures of details of their structure, to assess if drought has changed them.3) Install high-precision measurement tools ("dendrometers") on trees of key species, to enable better monitoring of future droughts4) Analyse data collected from (1) & (2) to test our hypotheses:1. The 2010 drought caused biomass carbon loss from forest but not savanna. We expect savanna to prove more resilient than forest, and for forest responses to mirror those of 2005.2. The 2010 drought accelerated tree death and reduced growth in the forest but not the savanna. We expect forest species to be more sensitive than savanna species when faced with the same degree of drying.3. Forest & savanna plots that had the greatest biomass loss and/or mortality are those with shallowest soils. We expect soil depth to affect the drought response, with shallower soils having fewer moisture reserves.4. Within each stand, species which also occur in drier areas were more drought-resistant than those already at the dry end of their range. We expect that the risk a tree faces from drought is related to its geographic distribution, so that species that are typically found in moister climates will be more drought-sensitive than their neighbours.5. Species differences in drought sensitivity are related to variation in structural traits. We expect the more drought-resistant evergreen trees will have a more conservative hydraulic structure, such as denser wood.The expected outcomes of this research are:1) Improved quantification of the sensitivity of transitional Amazon forest to drought.2) A first assessment of the differential sensitivity of forest and savanna trees to drought conditions.3) By integrating (1) & (2), understand better the chances of savanna replacing forest in the "zone of tension", and even into core Amazon forests, as the climate dries.4) Improved understanding of the physiological basis of drought-resistance and the importance of soil conditions.5) The infrastructure installed to allow local collaborators to evaluate effects during future droughts.