Influence of weather and climate on the growth patterns of common urban tree species

As climate change continues, cities are experiencing more heat and drought, causing further deterioration of growing conditions for urban trees. We investigated the growth of the commonly planted urban tree species Tilia cordata, Acer platanoides and Robinia pseudoacacia. The growth analyses are based on dendrometer data from permanent tree laboratories in two German cities with different precipitation levels: Munich with 940 mm/year and Würzburg with 570 mm/year. Species-specific growth patterns (quantity, growth initiation and duration) and the effects of site microclimate on stem increment were analyzed. Due to the high temporal resolution of the dendrometer data and the long recording periods of over 5 years, both long-term trends over several years and short-term reactions of the trees to external influences can be analyzed.

Additional to the species-specific differences, with lowest annual growth rates for T. cordata, significant trends show that precipitation and urbanization strongly dictate where trees grow the best. For both cities, cooler and greener sites revealed higher stem increment compared to warmer, highly sealed sites in the historic city centre. During 2021 more precipitation was registered (14 to 19% higher than the long-term average) in both cities. The most beneficial effect on tree growth is clearly shown for Munich, with approximately 50% higher increment for A. platanoides and 30% higher increment of T. cordata compared to the drier year 2022.

These results can support planning decisions on the selection of suitable tree species for urban locations.