DISSERTATION RESEARCH: Between a tree and a dry place - How competition and drought tolerance constrain tree geographic ranges

事实证明，确定物种范围的主要限制因素以及这些限制因素在全球范围内的变化是非常困难的；问题的关键在于，环境本身或与其他生物体的相互作用在多大程度上施加了限制。该项目将结合实验、实地研究和物种分布模型，以测试沿着从干燥到潮湿环境的梯度的植物物种是否在其范围的一侧因干旱而死亡，以及与适应潮湿条件的另一侧物种的激烈竞争之间受到挤压。研究结果可以帮助解释何时、何地以及如何限制树木范围的界限，从而推进科学的发展。这些信息可以帮助指导那些寻求为气候迅速变化的未来做好准备的土地管理者，指出哪些保护和预测工具适用于哪些情况，从而提高国家福利。还将通过高中生的科学教育活动，提高科学教育水平。长期以来，人们一直假设植物受到竞争能力和环境压力耐受性之间的基本权衡的约束，因为适应环境压力需要消耗大量的能量，并且限制了最大的生长速度。利用幼苗实验、树木年代学技术和物种分布模型，本项目探讨了美国和澳大利亚干旱梯度地区的树种是否表现出快速生长（竞争能力的代表）和耐旱性之间的权衡。然后测试这种权衡是否反映了田间成年树的生长限制，以及观察到的权衡和/或系统生长限制是否解释了物种在干旱梯度上的更替。为了产生更广泛的影响，将与高中教师合作开发和试点一个基于这项研究的模块，并将通过大学教学温室向公众传播结果。

Identifying the main constraints on species ranges and how these constraints vary across the globe has proven remarkably difficult; the degree to which the environment alone or in combination with interactions with other organisms imposes the limit is the crux of the problem. This project will combine experiments, field studies, and species distribution models to test whether plant species along a gradient from dry to wetter environments are squeezed between death from drought on one side of their range and fierce competition with species adapted to wetter conditions on the other. The results can help explain when, where, and how tree range boundaries are constrained, thereby advancing the state of the science. Such information may help guide land managers who seek to prepare for a rapidly changing climatic future by suggesting which conservation and forecasting tools are relevant in what situations, and thus enhances national welfare. It will also improve science education through activities for high school students.It has long been hypothesized that plants are constrained by a fundamental trade-off between competitive ability and environmental stress tolerance, because adaptations to tolerate stress are energetically costly and limit maximum growth rates. Using seedling experiments, dendrochronological techniques, and species distribution modeling, this project explores whether tree species inhabiting aridity gradients in the U.S. and Australia show a trade-off between fast growth (a proxy for competitive ability) and drought tolerance. It then tests whether this trade-off mirrors growth constraints on adult trees in the field, and whether the observed trade-off and/or systematic growth constraints explain species turnover across aridity gradients. For broader impacts a module based on this research will be developed and piloted in cooperation with high school teachers, and results will be communicated to the public through a university teaching greenhouse.