Forest fragmentation creates abrupt transitions (i.e., forest edges) which induce large gradients in key environmental drivers of tree ecophysiology (e.g., light, temperature, and soil moisture) between the forest edge and interior. However, we are only beginning to learn how these changes in environmental conditions alter tree carbon and water exchange with the atmosphere. We know that trees along a forest edge can grow more than twice as fast as trees in the forest interior (Reinmann and Hutyra 2017) and there is evidence that trees near a forest edge also use more water (Herbst et al. 2007), which in turn accelerates soil drying during the growing season (Reinmann et al. 2020). Our previous work has also demonstrated that while conditions near a forest edge can greatly enhance rates of tree productivity they can also make trees more negatively impacted by climate stressors such as excessive heat (Reinmann and Hutyra 2017). Despite these advances in understanding of how forest edge effects alter tree tree productivity and water use, we know very little about the underlying ecophysiological mechanisms. In this subproject we will conduct leaf-level measurements of gas exchange on canopy leaves from trees along forest edge-to-interior transects and across our precipitation treatments at CLIFF. In addition, we will conduct mini experiments on these leaves that will help us understand temperature sensitivities of gas exchange and to separate stomatal versus biochemical limitations to photosynthesis. This subproject may also incorporate measurements of tree sap flow (i.e., transpiration). A typical week may entail some combination of field work to measure leaf-level ecophysiological processes, maintenance and data downloads from sap flow sensors, compile/review literature on forest edges and tree ecophysiology, curating and analyzing datasets, and preparation for a final presentation. Collectively, we expect these measurements will provide data that advances our understanding of how forest edge effects and water availability alter tree ecophysiology modulators of ecosystem carbon and water exchange. We also expect this work to provide new insight into how water availability mediates the response of tree ecophysiological processes to heat stress.