Effects of pruning on growth and ecosystem services of plane trees in urban environment

Pruning is one of the most common management practices of urban trees to ensure safety, for aesthetic reasons or to remove dead plant parts. A tree’s growth performance and ecosystem services such as evaporation and shading can also be affected by pruning. This research study investigated how the growth of naturally grown Platanus x hispanica trees in Germany differs from that of table-topped pruned trees of the same species. The influence of this kind of pruning on photosynthesis, leaf area, growth and ecosystem services was demonstrated. We found that leaf level photosynthesis of table-topped trees was 20% higher and leaf level transpiration rate 56% higher than in naturally grown trees of the same age. Conversely, canopy photosynthesis and canopy latent heat flux was significantly lower in table-topped trees (47% and 82%). Our results clearly indicate a decrease in both size and diameter increment for table-topped trees compared to naturally grown trees, which confirms the reduction in the physiological processes photosynthesis and transpiration on canopy level. The changed physiology resulted in reduced stem diameter growth for table-topped plane trees in the year after pruning for 39%. Crown projection area and the crown volume of naturally grown plane trees is 2 times and 2.7 times higher than the ones of table-topped plane trees of the same diameter size, while leaf area is on average 30% larger for table-topped trees. The allometric relationships clearly differed. Our results show that specific environmental conditions should be considered when pruning trees in terms of growth and ecosystem services. A possible reduction in growth and services due to pruning can be mitigated by improving site conditions (e.g., low soil sealing, large root volume). However, especially in water-scarce environments or with high soil sealing, the reduction in transpiration following this type of tree pruning can be potentially beneficial. Our study, though, did not investigate sociocultural motives or aesthetic reasons for pruning. Our investigations focused exclusively on the growth and ecosystem services of a single species, P. x hispanica . Future studies should fill this gap by conducting a holistic study of the ecological, social, and aesthetic impacts of tree pruning that also includes other species with different growth and drought characteristics. • Table top pruning increases photosynthesis and transpiration of plane trees by 20% and 56% • In contrast canopy photosynthesis and latent heat flux were significantly lower • These resulted in reduced stem diameter growth of the pruned trees by 39% • Allometrics had changed: crown dimensions of pruned trees were > 2 times smaller • Leaf area is on average 30% larger for pruned trees