2016 | Dr. Susan Day, Virginia Tech
Can planting design and tree management be used to significantly increase stormwater mitigation by trees? Does presence of an urban forest understory or site maintenance practices such as leaf removal or mulching influence water infiltration and capture? Stormwater attenuation by urban forests is provided by a complex structural system that includes canopy interception, stemflow, and transmission into the soil. Plant characteristics, such as leaf morphology, architecture, and stem characteristics dictate canopy interception and stemflow. However, we hypothesize that the overall urban forest canopy structure, rather than characteristics of individual trees, has a greater effect on stormwater mitigation. Specifically, the addition of understory plantings could increase both canopy density and lead to soil surface traits that have already been identified as beneficial to stormwater capture, such as the presence of litter or mulch layers. We will examine three landscape structures in urbanized areas: trees only, trees plus understory, and understory only (defined as low shrubs or herbaceous plants) and evaluate them in terms of their effects on this stormwater mitigation complex. Sites will also be compared to a natural forest reference site, often used in policy development. This analysis will be replicated in a greenhouse study using the three plant structures in bioinfiltration cells with engineered soils where we will analyze changes in soil physical characteristics over time as well as rainfall partitioning using a rainfall simulator and lysimeters. Results can be used to optimize groundcover management beneath trees as well as to inform stormwater policy and runoff estimation models.