Insufficient space: Prioritizing large tree species and planting designs still fail to meet urban forest canopy targets

Abstract

The benefits associated with urban forests have led municipalities to set ambitious canopy cover targets to be achieved over the next few decades. Identifying tree species and planting strategies that can achieve these targets is crucial. We applied species-specific tree crown growth models for 20 species commonly planted in Melbourne, Australia to simulate canopy cover increase in newly developed residential suburb over 30 years (2025–2055). Tree species selection and planting strategies were simulated under high and low rainfall. The default strategy represented current tree species selection and planting practices. The two alternative strategies i) occupied all available street planting spaces prioritizing the planting of large crown species at maturity, and ii) occupied all available street planting spaces, maximizing the number of trees planted. Both the default strategy and maximising the number of trees planted achieved 11–15 % canopy cover after 30 years. Prioritising planting trees with large crowns at maturity achieved 16–22 % canopy cover after 30 years. Low rainfall reduced canopy cover in all scenarios by 4–6 %. Increasing the number of species with a large crown at maturity will likely achieve higher canopy cover. However, canopy cover targets will be difficult to achieve unless tree planting on private property increases.