Permeable ground, persistent effects: a decade of legacy growth in urban Tilia x europaea at Lindholmsallén, Gothenburg. Permeable ground as growth variable.

Abstract

Urban trees deliver critical ecosystem services ranging from transpiratory cooling and stormwater management to carbon sequestration and biodiversity support, however their capacity to provide these services is fundamentally shaped by the conditions of their immediate growing environment. Impervious ground surfaces restrict water infiltration, elevate soil temperatures, and impair root zone aeration, all of which constrain tree growth and long-term vitality. Measurements done between 2015 to 2016 demonstrated that a low fraction of permeable ground surface significantly suppressed both current-year shoot growth and, to a lesser extent, long-term stem growth in Tilia x europaea street trees along Lindholmsallén, Gothenburg. The present study revisits the same individual trees a decade later, with the aim of determining whether that permeability signal has persisted, strengthened, or diminished as the trees have aged and their urban context has intensified. Stem circumference and crown dimensions were re-measured in February 2026, and surface permeability was reassessed to account for both crown expansion and substantial ground surface alterations resulting from a decade of urban development, including the construction of large buildings and a tram line. The results reveal that yearly diameter growth is no longer significantly associated with surface permeability, likely reflecting a combination of age-related growth deceleration, probable exhaustion of confined root volumes, climatic stress including the exceptional 2018 drought, and construction-related disturbance. However, total accumulated basal area in 2026 shows a clear and statistically significant positive relationship with permeable surface fraction, with trees in the highest quartile of permeability access having accumulated 12.3% greater basal area than those in the lowest. These findings demonstrate that the influence of ground surface permeability on urban tree growth does not diminish with time but compounds as a structural legacy with direct consequences for the long-term ecosystem service capacity of street trees and for the planting decisions that determine it.