Stormwater runoff is an issue in urban areas as impervious surfaces increase. Various retention systems that incorporate trees have been developed but are expensive and require large amounts of space and cause their implementation to be difficult. We are investigating a system that is simple and mitigates the effects of stormwater runoff while increasing the urban tree canopy. Our full-scale prototype of this system has been constructed adjacent to a parking lot on Virginia Tech’s campus in Blacksburg, VA. It consists of a rectangular prism of a clay loam soil surrounded by a gravel moat filled with gravel. The system mitigates stormwater runoff by utilizing water uptake from three London planetrees planted in the soil prism. The gravel bed is intended to support an expansive root system that can absorb and transpire captured runoff while utilizing the soil for nutrients and anchorage. Adjacent to the gravel bed are three control trees of the same species, planted in the undisturbed native soil. The purpose of this study is to evaluate and compare tree performance and characterize the hydrology of the gravel bed. We are monitoring crown and root growth, photosynthesis, conductance rates, plant-water relations, and rainfall. The trees in the system have generally outperformed the control since being planted in May 2020.

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