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Journal of Environmental Horticulture






Horticultural Research Institute

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Microclimates characteristic of urban park, plaza, and canyon spaces were related to physiology and growth of even-aged sweetgum (Liquidambar styraciflua L.) street trees. Microclimates, tree growth, and physiological responses were characterized diurnally and seasonally. Park and plaza sites received unobstructed sunlight while the canyon was limited to four hours of direct solar radiation in midsummer. Potential seasonal insolation was 44 per cent of the potential maximum at the canyon and over 90 per cent at the park. Heating from paved surfaces at the plaza resulted in cumulative pan evaporation nearly 50 per cent greater than the other sites. Tree growth at the plaza and canyon acclimated physiologically and develop-mentally to the prevailing environmental conditions. Indicative of shade acclimation, canyon trees exhibited thinner leaves and less trunk growth when compared with the park; crown size and shoot growth were unaffected. In contrast, plaza trees, growing in a very coarse and shallow soil, were sparse and stunted. This was apparently due to leaf removal over time that eliminated nutrient cycling and progressively depleted soil nitrogen. Nutrient depletion apparently interacted with chronic high evaporative demand and water stress to limit the growth of the plaza trees. Park, plaza, and canyon designations of urban spaces provide a useful framework for predicting microclimatic factors that can affect tree growth for an urban site. Long-term growth and development, however, within any of these urban spaces will depend on interactions with existing soil conditions.