Effects of Climate and the Urban Heat Island Effect on Urban Tree Growth in Houston

Some studies have shown that urban tree growth is limited by many factors diverging from forest stands such as soil compaction, reduced soil aeration, limited nutrient and water availability, shading through buildings, high nitrogen inputs through pollutants and dog urine as well as vandalism. Especially, global warming can amplify the negative effects of urban microclimates on tree growth, health and well-being of citizens.

In this study, to quantify the growth of urban trees influenced by the urban climate, ten urban tree species in four climate zones were assessed in an overarching worldwide dendrochronological study. The focus of this analysis was the species water oak (Quercus nigra L.) in Houston, Texas, USA. And 183 water oak trees were chosen for data collection.

The results indicated that similar to the overall growth trend, the authors found in urban trees, water oaks displayed an accelerated growth during the last decades. Moreover, water oaks in the city center grew better than the water oaks growing in the rural surroundings of Houston though this trend was reversed with high age. Growth habitat (urban, suburban, rural and forest) significantly affected tree growth (p < 0.001) with urban trees growing faster than rural growing trees and forest trees, though a younger age of urban trees might influence the found growth patterns. Growing site in terms of cardinal direction did not markedly influence tree growth, which was more influenced by the prevalent climatic conditions of Houston and the urban climate.

Besides, higher temperatures, an extended growing season and eutrophication can cause an accelerated growth of trees in urban regions across, across all climatic zones. However, an accelerated growth rate can have negative consequences like quicker ageing and tree death resulting in higher costs for new plantings and tree management as well as the decrease in ecosystem services due to a lack of old trees providing greatest benefits for mitigating the negative effects of the urban climate.

Article by Astrid Moser, et al, from Germany and USA.

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Image by Kat Shaw, from Flickr-cc.