According to Yan Liu, a professor of geographical information science at the University of Queensland, and Rachel Gallagher, a Ph.D. candidate at the same institution, zoning has been the key tool used by urban planners to influence how our cities grow and change for almost a century.

"Contemporary zoning truly developed after the Second World War," the researchers wrote. "A combination of large real estate interests and the emerging field of urban planning created low-density, car-centric suburbs."

Urban plans called for standardized subdivisions and land uses, and engineering of streets and infrastructure.

Urban development was largely characterized by detached houses in residential suburbs, while large road networks separated these suburbs from commercial and industrial areas of the city.

However, in the late 1980s, many cities began to introduce planning mechanisms to restrict outward expansion. Changes in zoning allowed for increased density and a mix of land uses—the aim was to encourage redevelopment of existing urban areas.

Yet, as cities become denser and the traditional suburban "house and garden" is redeveloped, buildings are replacing trees, and settlements become grayer.

Replacing an existing home with a larger house or with several townhouses typically results in all existing vegetation being stripped from the site.

Compact city land-use policies and urban forest policies need to work together to ensure that there could be both high-quality built environments and extensive tree cover.

Experts argue that cities urgently need more strategic identification of small and large lots that are suitable for more intensified development, particularly to reduce the need for the widespread low-level consolidation that threatens tree cover.

At the same time, land-use regulation should ensure that both low-yield and higher-density redevelopment maintain the contribution of private land to the urban forest. Existing and new approaches to achieving this outcome need to be considered, whether that's done through local rules, government programs, or incentive schemes.

Rapid urban consolidation can change urban landscapes significantly over the next few decades, and the right decisions need to be made to ensure we don't end up with more "urban hell," which can be further explored in our previous publications on the subreddit here and here.