Tuesday, 26 June 2018

The Amazon on your doorstep

Our first slice of urban work, led by Phil, is out this week in Carbon Balance and Management (Open Access). We used a combination of TLS and the UK Environment Agency open lidar data to estimate the C density over the London Borough of Camden. We show that the 85K or so trees in Camden have a median C density of 50 t/ha, rising to 380 t/ha in spots such as Hampstead Heath and Highgate Cemetery.
Map of London Borough of Camden, showing the study area.

These are values that wouldn't be out of place in the Amazon, albeit over very small areas. The figure below show the C density over the whole borough.
C density across Camden.

Comparison of Camden C density values to other biomes.
The important aspect of this is not the total storage - clearly we are talking about small areas here! - it's that we are probably undervaluing the C storage capacity of trees in urban areas. And because we can choose where and how to plant them and can manage and protect them, they can grow very large and live long (and prosper). The other aspect we've found is that using allometric (size-to-mass) relationships for non-urban trees to estimate the mass of urban trees is problematic: due to their environment, urban trees have their own weird and wonderful shapes. TLS is the way to help quantify those differences.

I've written a piece for The Conversation on this work, which seems to have gone down well, and there's been some excellent coverage of the article including the Times, and then online science and tech blogs (phys.org, Metro, Reddit - 15K upvotes and counting!).

Various people who are involved in actually planning and implementing policy on protecting and managing urban trees were kind enough to provide quotes about our work:

Sir Harry Studholme, Chair of the Forestry Commission:
The trees in our cities are important. They matter because they are close to people and are a key component of our urban environment providing beauty, shade and homes for myriad species as well as absorbing carbon and pollutants. The work being carried out at UCL is adding colour and detail to this understanding.

Dr. Kieron Doick, head of the Forest Research Urban Forest Research Group:"Urban trees are a very important resource for all those who live in, visit or work in towns and cities, for they provide us with a plethora of health and well-being benefits, and they keep these places cleaner and more attractive. Canopy cover values released last year show that for some areas the abundance of trees is also higher than in the countryside (averaging: 16% (towns) and 10% (pan-England in 2016)). This means we should expect our urban trees to also be providing us will an important carbon sink, helping to combat the global trend of increasing carbon dioxide in the atmosphere. This new work by UCL is a welcome development in advancing this understanding, and I look forward to hearing how the work continues to develop."

Councillor Adam Harrison, Cabinet Member for Improving Camden’s Environment :"Camden is really pleased to partner with UCL, based in the borough, in order to unlock the benefits of trees not just for our own residents but for people's benefit round the world"
We want to expand this work to other cities, both in the UK and elsewhere. Clearly, C storage is just one of the ecosystem services provide, and by no means the most important. But, if we can assess their value more effectively in all ways, hopefully it will help us plan and build better, greener cities.
Scanning in the urban forest, Hampstead Heath.