Impact of Phytophthora Disease on the Growth, Physiology and Ecosystem Services of Common Lime (Tilia × europaea) Street Trees.

Tree diseases are a growing threat to ecosystem service provision by trees in cities and towns globally. Phytophthora is a widespread genus of plant pathogens (oomycetes) that have contributed to significant tree mortality worldwide; however, there has been little research into the impact of Phytophthora infection on urban trees or on ecosystem services important for urban populations, such as urban cooling. This study utilizes a network of Internet-of-Things linked sap flow sensors and point dendrometers collecting data every ~10 min throughout the growing season, combined with ground-based sampling (leaf chlorophyll content, Leaf Area Index), to monitor the impact of Phytophthora plurivora on mature Common Lime (Tilia × europaea) street trees, a globally common urban tree species known to be susceptible to Phytophthora. P. plurivora infection disrupted tree water flux, with an 87% reduction in median diurnal water use in infected trees (24.84 (IQR 77.04) L tree^-1 day^-1) compared with asymptomatic trees (198.36 (IQR 88.22) L tree^-1 day^-1). Infection also significantly reduced stem growth, with median shrinkage in infected trees of -0.22% (IQR 0.32%) compared with 0.35% (IQR 0.20%) growth in asymptomatic trees over the study period (May-October). However, infected trees with less disease damage were able to maintain growth and urban cooling similar to asymptomatic trees during the study period, highlighting the tensions between controlling disease spread and public safety hazards while maintaining ecosystem service provision. Our research raises questions about the impact of P. plurivora on other critical ecosystem services and in other common urban tree species and settings.