Urban trees match rainforests as carbon stores

Not just decorative, urban trees do much more: they enrich civic life, moderate climate change and save the taxpayer millions.

London researchers have identified a new reason for preserving urban trees. Woodland in the world’s great cities, originally intended to enhance the streets, can store as much carbon as a comparable stand of tropical rainforest.

Great concentrations of people in rapidly expanding cities are both driving climate change and at the same time increasingly vulnerable to the extremes of heat threatened by runaway global warming. So the finding is another reminder of the impact that megacities have both on climate change and on the answers to climate change.

Other research teams have already emphasised the direct value of green canopy in crowded urban streets: one study has calculated that megacities benefit to the value of around $500 million a year just by having tree-lined streets and shaded parks.

Urban trees are a vital resource for our cities that people walk past every day.

Phil Wilkes, University College London

Another has matched the foliage in the avenues with real estate prices to find that, in California at least, street trees add up to $1 billion to property values.

And, for once, urban foresters gain something from the increasingly warm and sometimes stifling conditions in the cities: street, garden and park trees flourish as the temperatures creep up.

London geographers report in the journal Carbon Balance and Managementthat they used airborne LiDAR data—the acronym is short for light detection and ranging—and ground measurements to generate a map of the carbon stored in 85,000 trees in just one area of London, the borough of Camden.

They found that parkland such as Hampstead Heath—a famous London open space—stored up to 178 metric tons of carbon per hectare: this is comparable with the 190 tonnes that are typically stored in tropical rainforests.

Trees have value: they provide shade, absorb rainwater, filter the air, and offer habitat for other creatures. One calculation suggests that the services delivered by London’s planes, oaks and horse chestnuts are worth $175 million (£133 m) a year in total: the carbon storage capacity alone is valued at $6.3m (£4.8m) a year. The next step is to take the technique beyond the boundaries of one local authority.

Vital resource

“An important outcome of our work was to highlight the value of urban trees, in their various and very different settings. The approach has been really successful so far, so we’re extending it across London, to other cities in the UK and internationally,” said Mat Disney, an author, and leader of the University College London geography LiDAR research group.

And his co-author Phil Wilkes, also at UCL, said: “Urban trees are a vital resource for our cities that people walk past every day. We were able to map the size and shape of every tree in Camden, from forests in large parks to individual trees in back gardens.

“This not only allows us to measure how much carbon is stored in these trees but also assess other important services they provide, such as habitat for birds and insects.”

This story was published with permission from Climate News Network.

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