Green belts 'effective' for curbing urban sprawl, Montreal study shows

Researchers at Concordia University say they have found an "almost always effective" way to curb urban sprawl, especially in big cities.

According to their study, the development of green belts on the outskirts of urban centres could help limit the increase in urban areas over a given territory, reducing harm to the environment. Green belts are protected areas, such as forests or agricultural land, which surround a city and even a region where real estate development is greatly limited or prohibited.

Parnian Pourtaherian, the lead author of the study published in academic journal Landscape and Urban Planning, says these spaces would prevent the often disorderly expansion of suburbs and certain economic activities.

Using open-source data, the researchers tracked the urban sprawl of 60 European cities from 2006 to 2015, half of which had a green belt. These were classified into four categories: very large cities (2.5 million inhabitants and more), large cities (more than one million), medium-large cities (500,000 to one million) and medium-sized (96,000 to 500,000).

According to this study, 90 per cent of cities with a green belt had experienced a decrease in urban sprawl during the given period. Conversely, only 36 per cent of the other cities had experienced such a decrease.

"We found great variability in green belt effectiveness across small, medium, and large cities," said Pourtaherian. "But the difference in relative changes in urban sprawl was more pronounced in larger cities."

Pourtaherian, who holds a master's degree in science from the department of Geography, Planning and Environment at Concordia University, says this method could also be used across Canada.

Ottawa and Toronto both have a green belt and Vancouver has a "Green Zone" to protect natural assets. On the other hand, Montreal still doesn't have a real green belt, but it urgently needs one, Pourtaherian says.

Effective if well regulated

For Jochen Jaeger, a professor in the department of Geography, Planning and Environment at Concordia, green belts are almost always effective, provided they are well supervised. Their effectiveness can be undermined if they are not properly protected or if they are too small or too narrow, he says.

"Some developers and politicians take advantage of the housing crisis argument to expand large residential estates and to allow additional low-density urban growth, or even to remove existing protective laws," said the co-author of the study. "They also apply salami tactics to chip away at the green belt by arguing that every little bit lost is just an 'insignificant' loss until there is nothing left."

A suburban sprawl may seem to go hand in hand with population growth, but its expansion puts residents further away from services offered in major centres on top of endangering the fauna and flora on the outskirts of cities.

"Limiting urban sprawl is crucial since it leads to the loss of green spaces and wildlife habitats and reduces ecosystem resilience due to habitat fragmentation, declining wildlife populations and extinction of local species," said Jaeger.

These effects will only be exacerbated by the climate crisis, he added, which will lead to higher expenditure on transport infrastructure, electricity distribution, water supply and wastewater collection. Urban sprawl is also associated with increased consumption of fossil fuels for transportation and the loss of fertile agricultural land.

Avoiding the expansion of low-density urban areas into natural spaces helps maintain the benefits of these spaces – including better air and water quality – which the current generation can then pass on to future generations.