The benefits of tree wounds: Microhabitat development in urban trees as affected by intensive tree maintenance

Abstract

In addition to social and economic benefits, urban trees provide habitats for many different species and contribute significantly to urban biodiversity. To prevent harm to humans or infrastructure, tree risk assessment is conducted regularly in urban areas. Resultant pruning activities are often criticized as leading to unnecessary injuries and artificial tree shapes. In this study we compared different tree maintenance levels and the occurrence of biodiversity related structures, so-called tree microhabitats, to provide another perspective on the consequences of pruning urban trees.For a sample of urban street and park trees in Montreal, Quebéc, Canada, we found that the positive relationship between tree size (diameter at breast height) and microhabitat abundance and diversity was less steep than in a nearby forest with comparable species composition. Intensive tree maintenance in urban trees led to levels of certain microhabitats such as cavities and injuries that were comparable to natural, unmanaged forests. Light maintenance of urban trees encouraged more crown deadwood than typical and intensive maintenance levels. Tree species as well as cardinal direction of the nearest building played a minor role in the occurrence and development of microhabitats.Our results underline the importance of conserving and maintaining large living trees, especially in urban areas to provide tree microhabitats. These results also demonstrate the important role of intensive tree maintenance in stimulating tree microhabitat development in urban areas. However, new ways have to be found to reconcile the need for microhabitats and the maintenance of structurally healthy urban trees.