Growth of street trees in Copenhagen with emphasis on the effect of different establishment concepts

Abstract

Limited rooting space is considered a major problem for growth of street trees. Different approaches to extend the soil volume accessible to roots have been implemented in Copenhagen, Denmark, during the last 15 years. The presented survey investigates growth and vitality of trees planted in 1) structural, load-bearing soil; 2) sand-based loadbearing soil; and 3) so-called super planting pits and trees planted in conventional planting pits. The trees were either street trees or situated on paved squares. The results provide evidence that vitality of recently established street trees in Copenhagen generally is on an acceptable level. Furthermore, tree growth in both of the load-bearing materials allowing for root growth was found to be comparable to tree growth in conventional planting pits, and those methods are therefore considered applicable at sites where conventional pits cannot be established. However, tree growth in super planting pits was superior to any of the other methods both in regard to growth rates and vitality. This method is therefore recommended wherever space for large planting pits with open surfaces can be made available. Growth of trees planted in conventional pits varied considerably, reflecting the broad range of different conditions the term "conventional planting" pit covers. © 2007 International Society of Arboriculture.