Långsiktigt kommunalt arbete med stadsträd och biodiversitet kan underlättas av inventeringar och lagstiftning

Sammanfattning

Biodiversity is in decline globally and locally. With a growing urban population, urban green spaces are shrinking, affecting local flora and fauna. Urban trees play a vital role in providing ecosystem services, such as creating habitable microclimates and preventing urban heat islands and flooding. Hosting a large number of species, urban trees – street trees and park trees – can help prevent species loss and serve as important stepping stones, connecting patches of suitable habitats in and adjacent to the city. In planning for climate change and climate adaptation, many cities resort to a broader variety of tree species. Exotic trees are favoured for their greater tolerance to heat stress and drought. This can however negatively affect native species composition. Further, many Swedish municipalities have densification goals for their built-up areas. Altogether, biodiversity goals related to trees can be difficult to achieve, in conflict with climate adaptation and urban development. This study investigates how municipalities in the Stockholm region are working with the above-mentioned issues. This is done by a survey distributed to ecologists and landscape architects working for Stockholm municipalities, complemented by an interview with a tree specialist. The aim was to investigate the long-term work with tree planning and inventories on biodiversity and urban trees, as well as conflicts arising with densification and climate adaptation. The study also aims at investigating how personal views and motivations amongst the respondents, as well as the content of planning documents, are reflected in the actual work being done. The results show a variety of approaches to biodiversity in relation to urban trees. A relatively consistent view states that exotic trees should be favoured in city centres, while native trees are preferred in the outskirts, although cultural heritage plays an important role. Further, building goals are difficult to combine with goals to preserve tree cover in cities. Amongst the municipalities, the use of inventories varied greatly in execution and implementation in long-term municipality work. The unanimous view was that biodiversity associated with urban trees is important, though resources on all fronts were lacking in order to fully address the issue. An important outtake from this study is the need for improved communication and cooperation between and within municipalities, as well as with private land owners. A deeper and more widespread understanding of existing inventories, along with standardized inventories, could make biodiversity work related to trees more effective. Longterm, the addition of exotics could help preserve urban biodiversity. Even though exotics generally host fewer species compared to native trees, they can support native biodiversity where native trees cannot.