Trees provide annual services worth USD 500 mn per magacity

New York: Trees provide each megacity with over USD 500 million every year in services that make urban environments cleaner, more affordable and pleasant places to live, a study of 10 magacities, including Mumbai, has found.

Megacities are home to nearly 10 per cent of the world's 7.5 billion people.

Researchers found that tree-based ecosystem benefits had a median annual value of USD 505 million, which is equivalent to USD 1.2 million per square kilometre of trees.

The value of trees' services was USD 35 per capita for the average megacity resident. It could easily be doubled by simply planting more of them, they said.

"Megacities can increase these benefits on average by 85 per cent," said Theodore Endreny from The State University of New York College of Environmental Science and Forestry in the US.

"If trees were to be established throughout their potential cover area, they would serve to filter air and water pollutants and reduce building energy use, and improve human well-being while providing habitat and resources for other species in the urban area," said Endreny, lead author of the study published in the journal Ecological Modelling.

The study estimated existing and potential tree cover, and its contribution to ecosystem services in 10 megacity metropolitan areas across five continents and biomes (a large, natural community of plants and animals that occupies a major habitat).

The cities were Beijing, Buenos Aires, Cairo, Istanbul, London, Los Angeles, Mexico City, Moscow, Mumbai and Tokyo.

The researchers estimated the benefits of tree cover in reducing air pollution, storm-water runoff, energy costs associated with heating and cooling buildings, and carbon emissions.

"Trees have direct and indirect benefits for cooling buildings and reducing human suffering during heat waves," Endreny said.

"The direct benefit is shade which keeps the urban area cooler, the indirect benefit is transpiration of storm-water which turns hot air into cooler air," he said.

Urban trees perform services most people are unaware of, including removal of airborne particulate matter dangerous to human respiration by capture on leaves.

They also provide energy savings in the form of cooling and insulation from both summer sunlight and winter winds; and carbon sequestration, which occurs when trees absorb and store carbon dioxide as they mitigate climate change.

"Placing these results on the larger scale of socio- economic systems makes evident to what extent nature supports our individual and community well-being by providing ecosystem services for free," said Professor Sergio Ulgiati of University Parthenope of Naples in Italy.