Collaborative Research: The other side of tropical forest drought: Do shallow water table regions of Amazonia act as large-scale hydrological refugia from drought?

覆盖地球的植被有许多重要的功能。植被的最大影响之一是捕获和储存大气中的二氧化碳。广阔的亚马逊雨林为这种碳储存功能做出了重大贡献。然而，亚马逊森林正受到最近气候变化的威胁，这使得干旱更加严重和频繁。一个很大的问题是，亚马逊是否会适应这些干旱，或者它们是否会减缓森林生长并杀死树木，这将释放碳。一个重大的挑战是缺乏关于亚马逊森林的大部分（约30%）的信息，这些森林的地下水位较浅，树木生活在水过剩的环境中。在这些被水淹没的森林里，树木生长缓慢，因为土壤条件不利于树根生长。在这里，干旱实际上可以通过减少这种水涝对树木有益。另一方面，这些森林的根生长在靠近土壤表面的地方，需要潮湿的条件。在这种情况下，持续很长时间的严重干旱会使上层土壤干燥，并可能进一步减少生长，比排水良好的森林中杀死更多的树木。该项目将回答地下水资源作为热带森林对干旱反应的重要控制的作用问题。有关森林生长和二氧化碳交换的数据将提供给更广泛的研究界。该项目还将帮助培训学生如何测量森林，并向公众提供有关热带森林的信息，该项目将测量巴西亚马逊地区森林冠层对干旱的反应。方法是将野外生态学与林冠塔和卫星对生态系统的远程观测相结合。在这个项目中建造的树冠塔--这是第一个在亚马逊内陆的积水土壤中建造的树冠塔--提供了关于树木生长的详细信息。将测量森林冠层的光合作用能力以及叶片的数量和物候。这一新知识将与现有的深地下水位深度站树冠塔网络、横跨亚马逊的卫星图像、森林调查网络提供的树木生长和死亡数据以及土壤水和其他环境因素的详细测量相结合。该项目将对影响森林碳循环的因素建立一个准确的新认识，同时对比积水与排水良好的土壤反应。一个基于数据的生态系统结构和功能模型将对亚马逊河流域的这些水涝森林对气候变化反应的贡献进行量化核算。这些结果有可能改变我们目前对热带森林干旱影响的看法。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The vegetation that covers the Earth has many important functions. One of the biggest impacts of vegetation is trapping and storing carbon dioxide from the atmosphere. The vast Amazon rainforest makes a significant contribution to this carbon storage function. However, the Amazon forest is being threatened by recent changes to climate, which is making droughts stronger and more frequent. A big question is whether the Amazon will be resilient to these droughts, or whether they will slow forest growth and kill trees, which would release carbon. A significant challenge is the lack of information about a large portion of the Amazon forest—about 30%—with shallow water tables, where trees live in an environment of excess water. In these water-logged forests, tree growth is slow because soil conditions are poor for tree roots. Here, drought could actually be beneficial to trees by reducing this water-logging. On the other hand, these forests have roots that grow close to the soil surface and require wet conditions. In this case, strong droughts that last a long time dry the upper soil and could reduce growth more, killing more trees than in forests with well-drained soils. This project will answer questions about the role of belowground water sources as an important control on response of tropical forest to drought. Data about forest growth and carbon dioxide exchange will be made available to the broader research community. This project will also help train students in how to measure forests, and provide information about tropical forests to the public.This project will measure forest canopy response to drought at sites in the Brazilian Amazon. The approach is to unify field ecology with remote observation of ecosystems from canopy towers and satellites. Canopy towers constructed in this project—representing the first of their kind in water-logged soils of the interior Amazon—provide detailed information about tree growth. The capacity of the forest canopy for photosynthesis will be measured as well as leaf demography and phenology. This new knowledge will be combined with networks of existing canopy towers in deep water table depth sites, satellite images spanning the Amazon, data on tree growth and death from a network of forest surveys, and detailed measurements of soil water and other environmental factors. This project will build an accurate new understanding of the factors that impact forest carbon cycling, while contrasting water-logged with well-drained soil responses. A data-based model of ecosystem structure and function will offer a quantitative accounting of the contribution of these water-logged forests in the Amazon to climate change responses. These results have the potential to transform our current perspective on drought effects in tropical forests.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.