The extent of stunting in trees growing within car parks compared with those situated in peripheral landscaped areas in the UK

Abstract

ABSTRACT Tree planting in towns and cities offers a range of important social, economic and environmental benefits; however, the harsh growing conditions of urban sites can substantially limit these benefits. This study investigated the effect of a car park environment upon the growth and development of trees planted within 13 sites in the UK. The size and condition of trees planted 11 to 27 years ago in restricted soil volumes surrounded by car park surfaces (n = 160) were compared to trees of the same age and species situated within the landscaped peripheries (n = 33) of 13 sites. Crown density was assessed at three sites planted with Acer platanoides L. as an additional measure of tree health. Analysis of stem diameter identified that trees in the landscaped areas exhibited 64.2% greater girth when compared to those planted in pits and 49.9% greater girth compared to those planted in strips within car park areas (excluding sites containing Platanus x acerifolia (Aiton) Willd., which coped well within car parks). Trees in peripheral landscaping areas were on average 20% taller in height and tree condition was significantly associated with estimated soil volumes. Sampled crown density also identified that the Norway maples within three car parks had around 30% sparser crowns than trees of the same species planted in adjacent landscaping areas. This study concludes that species and substrate conditions are crucial factors influencing the growth of most tree species in a car park setting. The stunted trees arising from inadequate car park design in the last three decades in the UK provide a sanguine lesson on how not to establish the urban forest of the future