Abstract/Summary

Local flooding events are common in urban environments where impermeable surfaces are becoming a dominant component of the landscape. Nature-based and space-saving solutions, such as hedge planting, create strips of permeable surface where excess water can percolate and reduce pressure on sewer systems. Previous summertime experiments found that the rate of plant evapo-transpiration (ET) is directly linked to replenishing the soil’s capacity to hold water, suggesting that plants with high ET rates would be beneficial in certain contexts to mitigate excess rainfall. This study investigates the rarely-studied winter ET rates/water use of five evergreen hedge species and cultivars. Three year old hedging plants were grown individually in 7.5 l pots in an outdoor field experiment (February-April 2021) in SE England. ET rates were measured at various intervals during this period and weather data collected from an adjacent weather station. We found significant species and cultivar differences in ET, with Thuja plicata ‘4ever Goldy’ consistently transpiring most on a per plant basis (on average over 150 mL/day even in average daily temperatures <5oC) and showing least variation in water loss in relation to solar radiation, but most in response to temperature. Thuja plicata ‘Atrovirens’ transpired most per unit leaf area (0.93 mL cm-2) and varied least in response to air temperature, but most in response to solar radiation. This suggests some scope for considering different types of planting to mitigate winter rainfall depending on the space available and prevailing environmental conditions. We are continuing with year-round monitoring with the view of linking particular plant functional and structural traits (canopy density/volume, branch angle, root system size) to the delivery of this ecosystem service.