Selecting public street and park trees for urban environments: the role of ecological and biogeographical criteria

Abstract

Street and park trees form an important component of the urban environment by supplying multiple benefits to the urban community. A tree species selection process describes the steps taken to identify a suitable tree species for a specific location. Research on urban tree species selection has confirmed the use of environmental, social and economic criteria. In contrast, ecological criteria, such as creating wildlife habitat, and biogeographical criteria, such as selecting indigenous species, and their potential conservation benefits have received little attention. Research in conservation biology has advocated the transformation of anthropogenic habitats to habitats for the joint use of humans and other species. Incorporating ecological and biogeographical criteria into a street and park tree selection process may help this transformation by addressing ecology and biogeography in a seemingly ‘unsuitable’ environment. This research aimed to examine the extent to which ecological and biogeographical criteria are used in street and park tree species selection and the potential use of ‘new’ ecological and biogeographical criteria in addition to existing tree selection criteria. This research attempted (i) to research the selection of street and park trees for urban environments, (ii) to identify potential ecological and biogeographical criteria for use in tree selection, (iii) to assess the extent to which street and park trees contribute to the ecology and biogeography of urban environments and (iv) to devise a decision-making support tool for tree selection incorporating proposed ecological and biogeographical tree selection criteria. This research focused on case cities in temperate New Zealand and Australia. Methods for data collection and analysis were taken from the social sciences and ecological studies. An interview technique was used to collect empirical data on the tree species selection process applied by municipal tree-care practitioners. Results were triangulated with policy document information from the respective city councils. The ecological and biogeographical component of this research was investigated through an extensive literature review and an exemplary tree inventory. The results revealed that few ecological and biogeographical criteria are used in urban tree species selection. Furthermore, municipal practitioners seem not to follow a standardised process in selecting street and park trees. Although many tree selection criteria are applied, their way of application appears still unclear. In addition, the results of the investigated parameters from the exemplary inventory showed that tree plantings in urban residential streets and parks probably contribute little to the ecology and biogeography of the urban environment. Based on these results a systematic tree selection decision support tool for municipal tree-care practitioners that includes ecological and biogeographical criteria was designed and applied in a theoretical manner. This tool theoretically verified the potential to integrate ecological and biogeographical criteria into urban tree species selection. Major barriers for their integration were identified. These included a lack of information and a lack of explicit statements in policy documents with regard to urban nature conservation. Furthermore, it was highlighted that education and understanding of ecological and biogeographical concepts may play an important role in applying ecological and biogeographical criteria in future tree selection.