Including Tree Diversity In Predictions Of Tropical Forest Drought Responses

热带森林是世界上最重要的生态系统之一;它们是生物多样性的热点，储存大量的碳，减缓气候变化，并影响全球天气模式。预测这些热带森林将如何应对气候变化是全球政策决策的优先事项。土壤湿度的长期减少和严重干旱事件预计将成为下一个世纪热带森林的主要威胁。如果未来遭受干旱，热带森林的命运将取决于哪些类型的树木死亡，哪些树木可以从幼苗存活到成年。了解这一点需要了解树木拥有哪些属性，这些属性会改变树木在干旱期间死亡或存活的风险，以及这些属性在不同类型，年龄或高度的树木之间如何变化。目前，大多数植被模型用于预测热带森林对未来气候变化的响应，只考虑有一个或两个固定类型的热带树木。它们只能解释不同树冠高度和位置的树木对干旱反应的非常有限的差异。因此，这些模型目前不太可能从树木特性的真实多样性中捕捉干旱反应的变化，而这些变化最终将决定热带森林对干旱胁迫的恢复力。在植被模型中代表热带森林干旱响应对树木特性多样性的依赖是复杂的。它需要关于不同功能类型和发育阶段的树木如何应对长期干旱胁迫的新数据。我的目的是收集必要的数据，以了解干旱生存的热带树木是如何与树木的属性和它们的变化在整个树木的发展在干旱条件下。我将使用这些数据来开发植被模型，并提供一个步骤的变化，他们如何代表热带森林干旱的反应。我有一个激动人心的机会来使用世界上运行时间最长的热带森林干旱实验，在过去的15年里，50%的降雨量被排除在外。在这里，我将测试不同发育阶段和不同属性的热带树木对长期干旱胁迫的反应是否不同，以及这如何影响死亡风险。我将详细的生理测量与树木在干旱中生存的能力，对重要的树木类群的不同大小的类，这些类群将包括物种被发现是高度敏感和耐干旱胁迫。为了配合这项研究，将在幼苗干旱实验中种植焦点分类群的幼苗，该实验将用于测试幼苗在之前暴露于干旱后是否具有抗旱性。最后，来自已经暴露于15年实验干旱的母树的幼苗和来自没有暴露于干旱的那些的幼苗将在实验室条件下生长并经受各种土壤干旱条件。这将测试是否在母树中预先暴露于干旱会诱导产生更耐旱的幼苗。我的研究将创建唯一的数据集，能够测试功能特性，发育阶段和干旱暴露如何控制干旱引起的死亡风险，以及哪些类型的树木最有可能从幼苗存活到成年，以维持未来干旱条件下的热带森林。这将为我的模型开发工作提供一个独特的机会，使用从单树模型到动态全球植被模型的模型层次。我的最终目标是代表干旱反应的重要差异，基于树木树冠的位置和它所拥有的属性，以便更准确地预测热带森林将如何应对未来的气候变化。

Tropical forests are one of the world's most important ecosystems; they are a biodiversity hot spot, store vast quantities of carbon, mitigate climate change, and influence global weather patterns. Predicting how these tropical forests will respond to climate change is a priority for making global policy decisions. Prolonged reductions in soil moisture and acute drought events are predicted to be a key threat to tropical forest in the coming century. The fate of tropical forests if exposed to drought in the future will depend on which types of trees die and which can survive from seedling to adult. Understanding this requires knowledge of which properties trees possess that alter their risk of dying or their survivorship during drought, as well as how these properties change between trees of different types, ages or heights. Currently most vegetation models used to predict the responses of tropical forest responses to future climate change only consider there to be one or two fixed types of tropical tree. They only account for very limited differences in how trees of different canopy heights and positions respond to drought. Therefore these models are currently unlikely to capture the variations in drought responses from real-world diversity in tree properties and which will ultimately determine the resilience of tropical forests to drought stress. Representing the dependency of tropical forest drought responses on the diversity of tree properties in vegetation models is complex. It requires new data on how trees of different functional types and developmental stages respond to prolonged exposure to drought stress. My aim is to collect the data necessary to understand how drought survivorship of tropical trees is related to tree properties and their variation throughout a trees development in drought conditions. I will use this data to develop vegetation models and provide a step change in how they represent tropical forest drought responses. I have the exciting opportunity to use the longest running tropical forest drought experiment in the world, a site where 50% of incoming rainfall has been excluded for the last 15 years. Here I will test if tropical trees at different developmental stages and with different properties respond differently to long-term drought stress and how this influences mortality risk. I will make detailed physiological measurements of properties associated with a trees ability to survive in drought, on important tree taxa of different size classes; these taxa will include species found to be highly sensitive and resistant to drought stress. To accompany this study, seedlings from the focal taxa will be grown in a seedling drought experiment which will be used to test if drought resistance in seedlings increases following prior exposure to drought. Finally seedlings from mother trees which have been exposed to 15 years of experimental drought and seedlings from those which have not been exposed to drought will be grown in lab conditions and subjected to various soil drought conditions. This will test if prior exposure to drought in mother trees induces production of seedling which are more drought-resistant.My research will create the only data-set which is able to test how functional properties, developmental stage and drought exposure control the risk of drought-induced mortality and which types of tree are most likely to survive from seedling to adult to sustain tropical forests under future drought conditions. This will provide a unique opportunity for my model development work, using a hierarchy of models from the scale of a single tree model to a dynamic global vegetation model. My ultimate goal is to represent the important differences in drought responses, based on a trees canopy position and the properties it possesses, to enable more accurate predictions of how tropical forests will respond to future climate change.