Shade from urban trees has long been understood to offer respite from the urban heat island effect, a phenomenon that can result in city centers that are 1–3 degrees Centigrade warmer than surrounding areas. Less frequently discussed, however, are the effects of tree transpiration in combination with the heterogeneous landscapes that constitute the built environment. Writing in BioScience, Joy Winbourne and her colleagues present an overview of the current understanding of tree transpiration and its implications, as well as areas for future research. Their work, derived from tree sap flow data, reveals the complexity and feedbacks inherent in trees' and urban zones' responses to extreme heating events. Dr. Winbourne joins us on this episode of BioScience Talks to discuss the newly published article, as well as directions for future research and the prospects for using trees to better mitigate urban heat in the face of a changing climate. Read this article in BioScience. Subscribe on iTunes. Subscribe on Stitcher. Catch up with us on Twitter.