Water Relations of Sweetgum in an Urban Canyon and Park

Document Type

Article

Journal/Book Title/Conference

Journal of Arboriculture

Volume

19

Issue

5

Publisher

International Society of Arboriculture

Publication Date

9-1-1993

First Page

266

Last Page

270

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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