Variable Urban Irradiance and Shade Acclimation in Norway Maple Street Trees |
Shade acclimation response of Emerald Queen Norway maple street trees to variable irradiance levels in an urban setting was investigated. Specific leaf area, trunk growth, and crown density were measured in thirteen sites ranging from urban canyons in the business core to open exposures in residential areas of Seattle, Washington. Percentage of potential seasonal input of global shortwave radiation for each site was modeled based on the azimuth and elevation angles of the surrounding horizon topography. Building height in the business core reduced estimated potential sea-sonal irradiance to 27%-90% of that for an unobstructed horizon topography, while those outside the business core had 90-95% of potential irradiance. As potential irradiance decreased these maples exhibited growth responses charac-teristic of shade acclimation in a dose-response pattern. Specific leaf area increased and trunk growth and crown density decreased to acclimated levels between 70-85% of potential irradiance. Shade acclimation did not detract from the appearance or utility of these trees in the urban canyon. Foliage of the canyon trees was healthy and lower crown density of these trees was not detectable without full-sun-grown trees for comparison. Supporting pdf: Variable Urban Irradiance and Shade Acclimation in Norway Maple Street Trees |
