Urban plants' role as carbon sinks 'underestimated'

The ecological services provided by urban trees are often overlooked, the study says

Plants in cities and towns make a major contribution towards removing carbon from the atmosphere, a study suggests.

The authors say the research is the first of its kind in Europe to quantify how much carbon is stored within this urban vegetation.

They add that the data are vital because local authorities are key in helping the UK reach its target of cutting CO2 emissions by 80% by 2050.

The findings will be published in the Journal of Applied Ecology.

In this study, the researchers used information from satellite data and from field research to survey the amount of vegetation across Leicester - a city with a population of about 300,000 people.

The assessment included domestic gardens, public spaces, road verges and derelict industrial land.

The team estimated that 231,000 tonnes of carbon, equivalent to 3.16kg per square metre, was locked away in the city's vegetation - most of which was stored by trees.

"Large trees are particularly important carbon stores," said lead author Zoe Davies from the University of Kent.

"Most of the publicly owned land across Leicester is grassland.

"If just 10% of this was planted with trees, the existing carbon pool across the city could be increased by 12%."

Urban world

The researchers noted that during the past century, the planet's urban population grew ten-fold. Now more than than half of the world's population is living in urban areas.

As a result of this rapid expansion, urban areas continue to grow at a faster rate than any other land-use type.

Yet, the team observed: "Despite the importance of urbanisation as a major driver of land-use change, there have been surprisingly few attempts to explicitly quantify the provision of ecosystem services at a city-wide scale.

"This is likely to be a legacy of the perception that urban ecosystems have limited ecological value because they are heavily modified by humans and relatively small in size."

Dr Davies said current assessments hold that once land in the UK is classified as urban, its biological carbon density is assumed to be zero.

"Our study illustrates that this is not the case," she explained.

"There is a substantial pool of carbon locked away in the vegetation within a city - another reason why urban trees and green spaces should be valued."

The study is part of £2.5m project, funded by the Engineering and Physical Sciences Research Council (EPSRC), that is investigating the size of the urban carbon footprint.

The programme, involving five universities, is divided into four areas: domestic buildings, non-domestic buildings (offices, schools, factories etc), transport and biological sequestration.