The governance of private residential land in cities and spatial effects on tree cover. Issue 62 (August 2016) - Daniel, Claire
Highlights: Trees on private land are an important component of urban green infrastructure with more than 55% of tree cover in Brisbane's residential suburbs existing over private land. The privately owned part of urban tree cover is influenced by a complex interplay of social preferences, dwelling density, and public policy. Private residential parcels developed since the 1990s have on average 30% less canopy cover than those developed before this time. Governance measures for most private residential land do not require development to protect existing trees or provide suitable spaces for large trees to grow. If development continues to follow the modern trend for large houses on smaller lots, a slow but permanent loss of private tree cover will occur. Abstract: Trees in cities supply ecosystem services, including cooling, storm water quality management, habitat, visual screening and softening of built form. There is an expanding interdisciplinary field encompassing biodiversity, ecosystem services, and stewardship networks in cities. However most of this work focuses on public greenspace. While much work has been done to demonstrate that trees on private land are an important complement to the public urban forest, and to understand the social drivers of such, less is known about the governance of private greenspace in cities. Private land contributes to a significant component of a city's tree cover, particularly in cities characterised by low-density residential suburbs. It is important to understand the mechanisms that govern private tree cover, given the pace and scale of urbanisation globally. We combined policy and spatial analysis to examine the influence of larger and denser forms of residential development on suburban tree cover and the scope of contemporary governance measures. We interrogated tree cover patterns in the rapidly densifying and consolidating city of Brisbane, Australia, to show that private residential tree cover is explained by dwelling density, housing age, terrain slope, high school education, and household income. Results show significantly (30%) less tree cover in low-density residential suburbs developed since the early 1990s. We develop five governance principles for reversing the decline of urban trees on private residential property that may be transferable to other rapidly developing cities in around the world.