Does early crown pruning stimulate root growth in young urban trees?

Urban tree planting programs often suffer from high early mortality rate due to transplant-related stress and root-shoot imbalance. Within this context, crown pruning has been proposed as a way to temporarily reduce transpirational demand and help re-balance the root-shoot relationship in newly planted trees. This study tested how different pruning techniques influence root system development, biomass allocation and leaf physiology in young Acer campestre L. and Carpinus betulus L. Specifically, the experimental questions focus on whether pruning intensity and cut typology can promote the production of new roots beyond the original root ball and improve traits linked to drought tolerance. Sixty container grown plants per species were re potted into 9.5 L air pruning pots and subjected to four canopy treatments: (1) topping cuts removing most apical buds on first-order branches, (2) reduction cuts redirecting growth to suitably sized lateral branch, (3) 50% defoliation per shoot without removing apices, and (4) unpruned control. Leaf physiology has been investigated 4, 5, 6 and 8 months after pruning (MAP). Photosynthetic contribution analysis was used to partition changes in net CO₂ assimilation into stomatal, mesophyll and biochemical components. After one growing season After one growing season, destructive measurements quantified shoot and root biomass, root-to-shoot ratio of newly formed organs, and fine versus conductive root fractions, alongside with basic wood anatomy and IAA levels in phloem. Unless the other pruning type, reduction cut has been carried out without altering the leaf physiology or the hormonal balance. Despite this, total root biomass changed little among pruning treatments, but both pruning types have increased the biomass and allocation of newly produced roots, as well as the proportion of absorptive fine roots. These results show how pruning did not negatively affect root growth and could be useful method to reduce root shoot unbalance during planting, i.e. lowering tree planting failure.