Water Relations of Trees Growing in a Green Infrastructure (GI) Storm Water Trench

Storm water management is a major concern for cities with outdated combined sewer systems. Uncontrolled storm water pollutes urban watersheds, and impairs the ecological function of streams and rivers. Storm water interception using urban green infrastructure (GI) installations planted with street trees will be a major contributor to improving overall runoff control. It is important to assess the performance of these trees to better understand their contributions to storm water management.

This research project focuses on water relations of trees in a GI tree trench system in the Mt. Airy section of Philadelphia. Acer rubrum ‘Armstrong’ and Platanus × acerifolia ‘Bloodgood’ were evaluated nearly daily at peak solar radiation from May through November for stomatal conductance (g_s), leaf water potential (Ψ_lf) and leaf area index (LAI). Using Ψ_lf and g_s  data from healthy specimens of similar age, the overall water stress of trees in these systems could be quantified. Water relation trends were evident, and analysis showed a significant difference between stomatal conductance rates of the two species, but not within species. Analysis of Ψ_lf data showed significant differences between the ranked data of the two species. In general, through the entire growing season, P. × acerifolia had greater stomatal conductance and lower susceptibility to water stress than A. rubrum ‘Armstrong’. These results suggest P. × acerifolia performs more successfully in these systems when compared to A. rubrum. These results could possibly be influenced by overall plant health, and species traits such as root structure (access to available water), and other traits that affect water relations.

This study provides some fundamental data on water relations and species performance in a GI tree trench system. With the increase of GI systems, continued research in plant performance is essential in developing successful stormwater management systems. Further research plans include assessment of performance throughout the entire course of a day, both seasonally and in consecutive days following significant rain events, determining overall evapotranspiration rates, and assessments of other species and GI systems.