Growth patterns and effects of urban micro-climate on two physiologically contrasting urban tree species

Abstract

Urban tree plantings for climate-adapted and resilient cities need to consider growth, vitality and ecosystem services of the planted tree species particularly during drought. However, information on growth and ecosystem services of urban trees under changed climate conditions are rare for most species. This study investigated the intra-annual growth patterns of two common but physiologically contrasting urban tree species: small-leaved lime (Tilia cordata) and black locust (Robinia pseudoacacia). Although meteorological variables at the study site in the outer city center of Munich, Germany for the year 2016 were similar to the long-term average climate (1961–1990) different growth patterns were found. This was mainly influenced by species characteristics (water use efficiency, wood anatomy) leading to different transpiration rates and reaction patterns to drought stress. Moreover, species’ drought reactions compared to past years were analyzed in detail with a retrospective dendrochronological approach. Distinct species patterns were identified, highlighting the greater drought tolerance and recovery of R. pseudoacacia compared to T. cordata. These results show that under a drier and warmer climate T. cordata can provide more canopy air cooling for short periods of time due to high transpiration, albeit this is at the expense of great water demands and following growth declines under water shortage. Contrary, R. pseudoacacia proved to be a more suitable and adapted species at sites with less water availability due to better water use efficiency, even at the cost of low canopy transpiration though higher soil moisture and latent heat exchange from the soil.