Water Relations of Sweetgum in an Urban Canyon and Park    (View PDF)

Roger K. Kjelgren and James R. Clark

Abstract: Water use and water relations of sweetgum growing in an urban canyon were investigated. Predawn water potential, dawn-to-dusk stomatal conductance, and leaf morphology were measured over a two-year period at a downtown site in Seattle, Washington. Trees received four hours of direct midsummer sunlight during midday. This was compared to similar-aged sweetgum street trees growing in a neighboring park-like setting. Specific leaf area and leaf presentation angle of the canyon trees were characteristic of shade acclimation. Stomata of the canyon trees quickly opened in response to light during the morning shade period, but closed rapidly in response to low humidity during the sunlit period, and remained closed through the afternoon shaded period. Overall lower conductances and leaf temperatures in the canyon trees resulted in transpiration rates that were lower than the park trees. The data suggest that trees growing in urban canyons will deplete soil water less rapidly due to the effects of reduced irradiance on tree transpiration.

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https://doi.org/10.48044/jauf.1993.042