2018 Urban Research Award: Water Use Efficiency in Urban Street Trees

Under the direction of Boston University Associate Professor Lucy Hutyra, Earth & Environment PhD candidate Sarah Garvey will examine water use efficiency among urban street trees in order to determine their climate sensitivity in relation to non-urban trees. Her research question is based on her lab’s recent work that suggests Boston’s street tree growth rates are ~4x higher than non-urban trees, but that those same trees have mortality rates at two times the rate of non-urban trees.

Garvey will directly monitor transpiration (water flow from the ground through the tree and then out the leaves) in urban and rural trees to examine water use efficiency (WUE) across tree conditions. WUE refers to the amount of CO2 uptake per unit of water transpired (lost to the atmosphere). Her hypothesis suggests that urban trees will transpire more and therefore have lower WUE as compared to rural trees, which would indicate that urban street trees are contributing more significantly to evaporative cooling in cities than previously estimated. If so, urban trees play an even greater role mitigating the urban heat island effect and moderating urban temperatures than previously thought.

Garvey will directly measure transpiration by installing sap flow sensors on urban for the 2018 growing season (May – September), using heat pulses as a tracer for tree water movement.

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