Tree growth rate under urban limiting conditions

Abstract

The benefits of green areas mostly depend on the trees’ dimension, which in the urban environment is not as predictable as it is in woodland. Growth models based on tree height and tree diameter at breast height have been largely employed to predict tree growth also in urbanised contexts. However, city environments differ from natural ones, and in addition to geographical influence, they present high variability in growth conditions within a few metres. Different urban conditions may influence tree vertical and diametral growth. The present study aims to jointly consider the effect of urban environment, maintenance practices and available space on the size growth of some tree species. Dendrometrical, space, management and status parameters of the sampled trees were collected during field surveys 14 years apart. Tree height and diameter at breast height data interpolations were realised and charted by an open-source graphing calculator to build three different growth equations (linear, logarithmic and logistic) for each of the five species considered regardless of tree growth conditions. The comparison between the comprehensive best-fitting models realised within this study and a USA inventory-based study highlighted quite similar tree growth trends, probably due to the consideration of both constrained and unconstrained trees. Furthermore, a study on the curves of same-growth condition trees of the same species was conducted. Generally, heavy pruning techniques such as control and pollard pruning, characterised by the removal of a consistent part of the tree crown, stand out as the main growth-limiting factor for the different species.