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Growth of Samanea saman: Estimated cooling potential of this tree in an urban environment

Ow, Lai Fern, Ghosh, Subhadip, Yusof, Mohamed Lokman Mohd
Urban forestry & urban greening 2019 v.41 pp. 264-271
Samanea saman, cooling, evapotranspiration, grasses, growth performance, heat island, leaf area, pavements, rain, soil properties, soil water, temperature, tree growth, trees
Trees facilitate cooling of an urban environment through evapotranspiration. Urban trees help mitigate the urban heat island effect. However, urban conditions are often undesirable for tree growth and this negatively impacts on the cooling ability of urban trees. This study investigated foliar and soil characteristics relating to the growth performance of Samanea saman –commonly planted tropical urban tree. The study was conducted on trees that had been growing for three years under three different growth conditions, in pavement, grass verges, and in structural soil. Trees in structural soil grew faster, were lusher despite a lower soil moisture present in the fast-draining engineered blend. The structural soil was compacted to meet pavement load bearing requirements. The evapotranspirational cooling by trees in structural soil was approximately 75% higher compared with trees planted in pavements, and 50% greater than those in grass verges due to greater leaf area. In April, when temperatures were high and precipitation low, estimated cooling potential of the larger trees in structural soil was 8.5 kW while in July when temperatures were slightly lower with no change in rainfall, cooling was estimated to be 28% lower. By comparison, cooling was 76% and 81% lower for trees in pavement during the same period. The greater potential of structural soil resulted in evapotranspirational cooling.