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Open AccessArticle

Identifying Tree Traits for Cooling Urban Heat Islands—A Cross-City Empirical Analysis

Department of Geography and Geology, University of Salzburg, 5020 Salzburg, Austria
Institute of Forest Botany and Forest Zoology, TU Dresden, 01069 Dresden, Germany
Department of Climatology and Landscape Ecology, University of Szeged, 6722 Szeged, Hungary
Evolutionary Ecology of Plants, Department of Biology, Philipps-University Marburg, 35043 Marburg, Germany
Department of Biosciences, University of Salzburg, 5020 Salzburg, Austria
Institute of Ecology and Botany, Centre for Ecological Research, 2163 Vácrátót, Hungary
Author to whom correspondence should be addressed.
Forests 2020, 11(10), 1064;
Received: 3 September 2020 / Revised: 23 September 2020 / Accepted: 30 September 2020 / Published: 30 September 2020
Research Highlights: This paper presents a cross-city empirical study on micro-climatic thermal benefits of urban trees, using machine-learning analysis to identify the importance of several in situ measured tree physiognomy traits for cooling. Background and Objectives: Green infrastructure and trees in particular play a key role in mitigating the urban heat island (UHI) effect. A more detailed understanding of the cooling potential of urban trees and specific tree traits is necessary to support tree management decisions for cooling our progressively hot cities. The goal of this study was to identify the influence and importance of various tree traits and site conditions. Materials and Methods: Surface temperature, air temperature at 1.1 m and at tree crown height, as well as wet bulb globe-temperature of shaded and fully sun-exposed reference areas, were used to study the cooling effect of seven different urban tree species. For all 100 individuals, tree height, crown base, trunk circumference, crown volume, crown area, leaf area index (LAI) and leaf area density (LAD) were measured. Measurements were conducted in the cities of Dresden, Salzburg, Szeged, and Vienna as representatives for middle European cities in different climate zones. Results: Beside site conditions, tree species, height, height of crown base, as well as trunk circumference, have a great influence on the cooling effect for city dwellers. The trunk circumference is a very valuable indicator for estimating climate regulating ecosystem services and therefore a highly robust estimator for policy makers and tree management practitioners when planning and managing urban green areas for improving the availability and provision of ecosystem services. View Full-Text
Keywords: microclimate; tree physiognomy; random forest microclimate; tree physiognomy; random forest
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MDPI and ACS Style

Helletsgruber, C.; Gillner, S.; Gulyás, Á.; Junker, R.R.; Tanács, E.; Hof, A. Identifying Tree Traits for Cooling Urban Heat Islands—A Cross-City Empirical Analysis. Forests 2020, 11, 1064.

AMA Style

Helletsgruber C, Gillner S, Gulyás Á, Junker RR, Tanács E, Hof A. Identifying Tree Traits for Cooling Urban Heat Islands—A Cross-City Empirical Analysis. Forests. 2020; 11(10):1064.

Chicago/Turabian Style

Helletsgruber, Carola; Gillner, Sten; Gulyás, Ágnes; Junker, Robert R.; Tanács, Eszter; Hof, Angela. 2020. "Identifying Tree Traits for Cooling Urban Heat Islands—A Cross-City Empirical Analysis" Forests 11, no. 10: 1064.

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