Abstract
Tree planting is widely advocated and applied in urban areas, with large-scale projects underway in cities globally. Numerous potential benefits are used to justify these planting campaigns. However, reports of poor tree survival raise questions about the ability of such projects to deliver on their promises over the long-term. Each potential benefit requires different supporting conditions—relating not only to the type and placement of the tree, but also to the broader urban system within which it is embedded. This set of supporting conditions may not always be mutually compatible and may not persist for the lifetime of the tree. Here, we demonstrate a systems-based approach that makes these dependencies, synergies, and tensions more explicit, allowing them to be used to test the decadal-scale resilience of urban street trees. Our analysis highlights social, environmental, and economic assumptions that are implicit within planting projects; notably that high levels of maintenance and public support for urban street trees will persist throughout their natural lifespan, and that the surrounding built form will remain largely unchanged. Whilst the vulnerability of each benefit may be highly context specific, we identify approaches that address some typical weaknesses, making a functional, resilient, urban forest more attainable.
Highlights
Greening our cities might be thought of as the archetypal urban sustainability solution
Other frequently identified conditions were that the tree is large or mature, that high levels of canopy cover exist in the surrounding urban area, that the tree is maintained for amenity, that people are present nearby, and that the tree is visually accessible to the public
Several conditions that are necessary for delivering one intended benefit are considered likely to undermine the delivery of other benefits. These conditions include those that relate to the presence of a large or mature tree, the presence of large-scale tree cover, the tree being maintained for wildlife, the surrounding area being built to high-density, and the tree being physically accessible to the public
Summary
Greening our cities might be thought of as the archetypal urban sustainability solution. Whilst the financial [8] and natural resource [9] costs may be considerable, such planting programmes typically claim that a wide range of sustainability benefits will be delivered; including, but not limited to: building energy savings, improved air quality, carbon capture, increased biodiversity, improved water quality, and direct improvement of human health and wellbeing [7,9,10]. There are drawbacks associated with increasing urban tree cover that need to be considered, typically referred to as disbenefits or disservices [22,23]
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