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Why we’re mapping a million trees and more!

Updated Wednesday, 27 November 2019
Dr Phil Wheeler, Dr Nadia Dewhurst-Richman and Janice Ansine look at the benefits of trees, plus discuss the work of Treezilla.

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Trees have been in the news a lot recently with political parties trying to outdo each other on tree planting pledges. As the climate crisis has risen up the political agenda, trees and tree planting have been recognised as an important response since they take up carbon dioxide from the atmosphere as they grow. A recent study [1] found that a global tree planting effort aimed at increasing tree cover by 0.9 billion hectares would help to remove two-thirds of all human-produced carbon dioxide.

But amid the clamour for more trees, for the many people involved in looking after trees and woodlands the over-riding concern is that we aren’t taking enough care of our existing trees. Part of the problem is that we simply do not know enough about the trees that we have, this is particularly true of urban trees. In fact we know less about trees in towns and cities than we do about those in the wider countryside, despite many urban areas having a higher tree canopy cover than much of the countryside.

Poplar trees in autumn Teardrop Lakes Milton Keynes Poplars in autumn, taken at Teardrop Lakes in Milton Keynes.

As well as taking in carbon dioxide, urban trees provide a number of important benefits to the more than 80% of the UK population that live in towns and cities. Trees take-up air pollution, help reduce flood-risk by increasing the evaporation of rain before it reaches the ground and channeling water into the soil instead of letting it flow over the surface. Trees also reduce the ‘urban heat island’ effect, making cities cooler in the heat. So they can both help to address the causes of climate change and to mitigate its effects. More than this, urban trees are vital parts of our natural and cultural heritage: think of the Plane trees that line the Mall in London or the Sycamore tree at Hadrian’s Wall, one of the most photographed trees in the UK.

Trees also play an important role in supporting our mental as well as physical well-being. With all these benefits, you might think that urban trees are well documented, cared for and protected, but this couldn’t be further from the truth. Despite recent commitments to planting and spending on maintenance, urban trees are very poorly monitored and it’s not known whether the amount of urban tree canopy is increasing or decreasing [2]. What is known is that the average lifespan of an urban tree is substantially less than its rural counterpart, and urban tree-felling in some places greatly exceeds the recommended rate and has resulted in public protests.

Treezilla saw the entry of its one millionth tree record in the database which equates to annual benefits (e.g. air pollution, storm water filtration) worth £95 million.

Insufficient urban tree data for monitoring reflects issues with land ownership, (many trees are privately owned and therefore not routinely monitored), and inconsistent data collection methods used by tree officers employed by local authorities. Furthermore, many local authorities do not have comprehensive tree inventories and only a tiny fraction of the inventories that do exist are publicly-available. In 2013 Treezilla was created, a citizen science project which aims to map every tree in the UK and make the data publicly-available, with the aim of being a one-stop-shop for urban tree data for use by the public, researchers, government and business. However, a dataset of the right information compiled using consistent methods allows us to estimate the benefits of urban trees thereby answering a number of critical questions that would help to leverage more funding support to protect our urban forests.

In June 2019 the Geospatial Commission awarded funding for members of the Treezilla team and other partners to address the issue of the fact data is collected in an inconsistent way and secondly the lack of urban tree data. Through a series of workshops and consultations with the urban tree stakeholder community the project will produce guidelines for carrying out tree surveys with the aim of standardising the way in which urban tree data is collected. Secondly, the project will produce a new optimised Treezilla website and mobile app that will improve the whole data collection process for amateur tree data collectors through to the more experienced data collector.

Trees on the Open University Campus, Walton Hall, Milton Keynes Trees at the Open University in Milton Keynes. This month (November 2019), just in time for the annual National Tree Week [3], Treezilla saw the entry of its one millionth tree record in the database which equates to annual benefits (e.g. air pollution, storm water filtration) worth £95 million [4]. Of course the wider value of a tree is much more than these physical processes. And as we develop the tools in the site we are also incorporating methods for assessing the amenity value of a tree, based upon the widely adopted CAVAT tool. But there will always remain other intangible values that we as individuals attach to trees around us. We don’t need to quantify the meaning of the local children’s favourite climbing tree, or an ancient oak in a village green to understand their value. Perhaps it is these values that should be the real reason that we do all that we can to protect, maintain and enhance our urban trees. And to do that we must start with mapping them!

To help build the Monster Map of Trees, visit the Treezilla website: Look out for a new, quicker, slicker site and apps in time for mapping trees next spring / summer 2020! If your organisation has data you might like to add to the site, or if you are involved in collecting data on urban trees and are interested in contributing to the data standards consultation, contact


Further reading and references

[1] Bastin et al. (2019) The global tree restoration potential. Vol. 365 (6448) pp. 76-79.


[3] 23 November to 1 December 2019, is National Tree Week, the UK's largest annual tree celebration, marking the start of the winter tree planting season. Why not join in this year? Be a #TreeChampion this #NationalTreeWeek: add your local trees to or for information on other ways to get involved go to the Tree Council:

[4] This calculation is based on data from approximately 335,000 trees as the remainder of the dataset had insufficient data for ecosystem service economic benefit calculations. We are working to address this data gap.


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