Trees in urban and city environments : a review of the selection criteria with particular reference to nature conservation in New Zealand cities

The overall aim of this research was to review the general criteria for selection of trees for urban environments and city environments. The reason for this research was to assess the extent to which criteria for tree selection can contribute to nature conservation in cities. We conducted an extensive review of the literature, looking for publications about the selection criteria. In particular, we looked for any previous published reviews of the criteria. With reference to the criteria used in New Zealand, we undertook an unstructured review of the practices adopted in most cities. A review of the literature revealed many publications about different criteria but only one publication in which there was a general review of the criteria used for selecting trees for urban environments. By way of contrast, lists of tree species deemed to be suitable (or unsuitable) for urban planting are widely available, and some include information about selection criteria, but often with little background explanation. Worldwide, commonly used criteria included commercial availability of species, compatibility with urban environments, landscape design, low maintenance, avoidance of nuisance factors and historical practice. The most common criteria are concerned with the concept of choosing species compatible with local climate and soils. Anecdotal evidence suggests that more and more cities are using a mix of criteria including those that may contribute to conservation and restoration of native biota. We suggest that there should be greater use of ecological, genetic and biogeographical criteria to meet the needs of nature conservation in New Zealand cities