Urban tree cover targets: The good, the bad and the SMART
Justin Morgenroth, Kieron J. Doick, Richard J. Hauer, Dexter H. Locke, Camilo Ordóñez, Lara A. Roman, Tenley M. Conway, Cynnamon Dobbs, Peter N. Duinker, Natalie Marie Gulsrud, C.Y. Jim, Andrew K. Koeser, Shawn Landry, Stephen J. Livesley, Lorien Nesbitt, Charlie M. Shackleton, Puay Yok Tan, Jun Yang
Abstract
Urban tree cover (UTC) is a commonly used metric in policy and management activities, including urban forest resources assessment, equity and distribution, and ecosystem services modelling. Despite the well-established benefits associated with urban tree canopy, declining tree cover has catalysed many cities into setting UTC targets. In this short communication, we used an assessment of UTC targets set by 57 cities worldwide to discuss the merits and drawbacks of setting UTC targets and to inform recommendations for setting effective UTC targets. We found that UTC targets range in ambition, varying between 4% and 50%. To meet these targets, cities would have to increase their current UTC by between 0.47 and 23.3 percentage points within stated timelines of between 3 and 51 years. We found that cities with lower current UTC set ambitious targets, requiring relatively large annual increases in UTC. Moreover, cities in xeric or dry biomes set lower targets (< 20%) than cities in temperate or tropical biomes (> 25%). We found that setting UTC targets can provide a range of benefits, but achieving a UTC target at the expense of other indicators of urban forest structure and quality poses risks. We reflect on pathways to set specific, measurable, achievable, resourced, and time-bound UTC targets, while acknowledging the associated issues. This exploration of UTC targets will help ensure that UTC remains a useful metric for urban forest management and planning.