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以及这些限制在全球范围内的变化非常困难；环境本身或与其他生物的相互作用施加限制的程度是问题的症结所在。这个项目将结合实验、实地研究和物种分布模型来测试从干旱到更潮湿环境的梯度上的植物物种是否受到挤压，一方面是干旱导致的死亡，另一方面是适应更潮湿条件的物种的激烈竞争。这些结果可以帮助解释何时、何地以及如何限制树木范围边界，从而推动科学的发展。这些信息可能有助于指导土地管理者，通过建议哪些养护和预测工具在何种情况下是相关的，从而为快速变化的气候未来做好准备，从而提高国家福利。它还将通过高中生的活动来改善科学教育。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根本权衡的限制，因为适应耐受压力的能力是昂贵的，并限制了最大生长速度。利用苗木实验、树种年代学技术和物种分布模型，该项目探索了美国和澳大利亚干旱梯度的树种是否在快速生长(竞争能力的替代)和耐旱性之间表现出权衡。然后，它测试这种权衡是否反映了田间成年树木的生长限制，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周转。对于更广泛的影响，将与高中教师合作开发和试行基于这项研究的模块，结果将通过大学教学温室向公众公布。

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.