The impact of air pollution on growth features and the health of trees in Berlin

This study examined the impact of air pollution, and more specifically the impact of traffic, on the health of urban trees. Due to the lack of data sets, urban tree growth modeling often relies on the existing knowledge of forest. However, urban trees differ from forest trees. One of the aims of the study is to fill the lacunae in this field. It was hypothesized that in streets with higher traffic volume, both growth parameters and health status of trees would be decreased in comparison to trees growing in streets with lower traffic volume. Four of the most common tree species growing in Berlin were selected: Tilia cordata Mill., Acer platanoides L., Platanus acerifolia (Aiton) Willd., and Aesculus hippocastanum L. Apart from the tree age and stand position (high and low traffic volume), the height and circumference were measured and the following traits were analyzed: trunk condition, crown defoliation, leaf discoloration, the presence of hollows and nests. The streets that were selected for the analysis were located in the center of Berlin. For each species, four streets with high traffic volume and four streets with low traffic volume were chosen. The car traffic volume had a significant impact on growth parameters. Significant differences in height and circumference between trees growing on streets with low or high traffic volume were noticed; the higher the traffic volume, the lower the tree height and circumference. This tendency is particularly visible in P. acerifolia, T. cordata and A. platanoides. This relation was observed in all species except for A. hippocastanum. In the conditions of high-traffic volume, A. platanoides is thriving revealing the smallest differences in vitality and condition of the crown, trunk and leaves. The greatest differences in the health condition of the trees among the analyzed variants of traffic intensity were observed in the case of T. cordata. Lime trees seem to be most suitable for planting in the streets with lower traffic volume, whereas A. platanoides seems most suitable for planting in the streets with high traffic volume. P. acerifolia, despite its generally good health, is suffering from several progressing diseases. It is worth considering whether it should be gradually replaced with more resistant species. Aesculus, especially A. hippocastanum, are currently the most endangered ones. An alternative to this species can be A. carnea.