By Zaria Greenhill & Paul de Zylva


The Root of the Problem: why are mature trees felled in urban areas?


Imagine you live in a Victorian house in Lewisham. You’re comfortable, you know the neighbours and the nearby amenities, it’s generally peaceful and offers security and a sense of place. It’s your home.


And then you see a crack in the wall. Worried, you contact your insurance company and, after some investigations, they point to the large plane tree in the street outside and declare that it’s for the chop. This seems disappointing. There are birds in it in summer and you realise that the shade does keep your south-facing home cooler in summer heat. But you’re briskly told that the council will fell the tree on request, problems solved.


But hang on a minute, does a perfectly healthy tree have to go, just for a crack in the wall?  Is it really that easy?


London’s Forest’

London is a very green city, which is one of the things that makes it relatively cleaner and more liveable than some other megacities. In Lewisham, we have just over 17% tree cover, which makes us among the bottom third of London’s 32 boroughs (highest is Barnet, shaded by 26% tree cover).

In the UK overall, however, we have a severe problem with the loss of nature and biodiversity. In the international ‘Biodiversity Intactness index’ UK ranks 12th worst globally, and lowest out of all G7 nations, having retained only 50% of its biodiversity in face of human pressures. So, we’d better try and save whatever we can of the remaining nature and biodiversity, and trees in particular are important as they provide habitats for other species, such as invertebrates and pollinators, which are important for our gardens and parks and allotments, fungi and birds. Mature trees are housing estates for birds every year as they build nests for their young.

Rather surprisingly, the city’s trees have a price tag, in terms of the ‘ecosystem services’ they provide. The entire sum is £137,200,000 per year[1], for ‘services’ include urban cooling, support for wildlife, as mentioned above, flood water absorption and some species can even absorb air pollution as well. And we love them: the aesthetic value in trees is well documented and is reflected in the fact that streets with trees tend to have higher financial value. The uncomfortable correspondence between wealth and tree cover on a Lewisham level, one of the hidden aspects of social inequality in our borough, is laid out in Climate Action Lewisham’s statement on mature trees here.


Shifting ground

Back in the Lewisham Victorian house (more costly because of the trees) we learn that the worrying cracks are due to subsidence. This is when the ground beneath a building shifts or shrinks and the building moves around, or possibly sinks with its own foundations. It’s common on the heavy Eocene clay soil under most of London and the South East: it retains water in the winter and can dry out as hard as concrete in the summer. You can sometimes see cracks in the ground in parks in hot weather, that’s proof that the ground is moving, and it can damage buildings. Greater climate-related extremes of weather exacerbate this, and, some say, so do trees.

Obviously trees ‘drink’ water from the soil, especially in dry weather. This makes them incredibly useful when there’s an excess of water, such as in a storm or flood (they improve soil quality so that it can absorb more water, and hold a quite surprising amount in canopies in the short term, avoiding the overwhelm of those Victorian drains that often causes surface water flooding), but as their roots search for water there’s a risk of exacerbating subsidence in clay soils. However, in a context of increasing climate-related extremes of temperature, it’s complex to pin the ‘fault’ for subsidence on trees. It’s too easy to assume that a large tree will inevitably cause subsidence and that any problems may not be outweighed by the value the tree brings to its surroundings. It’s common to find cases of subsidence where there are no mature trees nearby.


What do the experts say?

 The Association of British Insurers, the last word in authority on insurance matters, says:

  • “Cracking in properties can occur for reasons unrelated to subsidence. These include the natural settlement of soil under new homes or extensions, thermal and humidity expansions or the drying and shrinkage of building materials (including freshly plastered walls).”


The Royal Horticultural Society says:

  •  “Most trees growing near buildings cause no damage. But in some cases, subsidence and structural damage can be linked to tree roots. Blocked drains and lifted paving may also be a problem. Understanding the factors involved in tree damage to buildings, including soil type and depth of foundations, will help both tree and house owners determine what action to take and when to get professional help.”

 Of course, not all trees are the same and species with finer and longer root systems, such as poplars, willows, elms and oaks are more associated with insurance claims. According to Local Surveyors Direct, 70% of all valid claims are tree-related, and they take longer, cost more and are more difficult to resolve than any other causes of subsidence.


Pointing to the lack of proper evidence of trees being to blame, Arboricultural consultants Sylvanarb say:

  • “Where structural damage to a property has occurred, trees within close proximity are often cited as being the most likely cause of damage…All too often a tree will initially be identified as the cause of damage, sometimes without all necessary investigations having been carried out.”
  • “Mature trees often compliment and add value to a property. However, many surveyor reports highlight existing trees as being a potential threat to a building. This can invariably lead to misplaced concern and unnecessary precautionary tree removal.”

Notably, Local Surveyors Direct say that

  •  “Even with fairly detailed investigations, it is not possible to make an accurate prediction as to which trees from amongst the total population will actually initiate damage.”


The London Tree Officers Association (LTOA) says:

  • “Tree Officers frequently receive requests that action be taken against a particular tree, or trees, either because they may possibly at some future date cause problems with a building, or because they are already suspected of having caused a problem with the foundations of a nearby property.”


Is it the case that our insurance company is requiring the precautionary removal of the tree? Just in case it causes problems in future?  But rather than being expendable, is that tree actually protecting the home from other issues, such as the baking effect of direct sunlight into a poorly-insulated Victorian home in summer? And would the area be hit harder if there’s a flood locally? And what if the local inhabitants love that tree and the beauty it bestows on an ordinary suburban street? What price a tree?


So why are trees so often felled as a supposed response to subsidence?

The insurance industry started providing subsidence cover for homeowners in the early seventies. During the famously long hot summers of 1975 and 1976, claims reached a value of £500m. By the late eighties, tree-related claims rose, and by the nineties 2,841 claims made between 1990 and 1992 alone. Skip forward to 2018 and 2,500 claims costing a total of £14 million were made in the spring of that year alone.

2018 was declared the joint hottest summer on record, with 1976, 2003 and 2006, as wildfires burned on the moors near Manchester and a couple of vehicles sank into melted tarmac. Mid-July saw a high of 32.5 degrees in the south. Probably not coincidentally this was the summer both Climate Action Lewisham and the international movement Extinction Rebellion boiled up, and as a direct result of the heat subsidence-related claims leapt to 10,000 and cost £64 million.


What’s the situation in Lewisham?

Lewisham Council look after approximately 30,000 trees in our borough (that’s about 1 tree per ten residents), although official numbers vary. This does not include trees on private land, such as in private gardens. There is one council officer to oversee their care, due to long term austerity measures (over half the local authority’s overall budget goes on health and social care: there is little left over for trees). The great risk to the council is that if one of their trees is considered a threat they are financially liable for any damage it may cause, including subsidence. In the case of property with cracks the local authority may be compelled to fell the tree whether there is strong enough evidence for its detrimental effect or not, or irrespective of whether its value is seen as higher to the council, the homeowner or the community (or the wordless birds and bugs), because should the cracks worsen, or the property becomes unstable, the local authority become legally liable. The bill can run into millions and it strikes understandable terror into the hearts of the council budget-managers. The threat to trees in Lewisham, as in many other areas, is from financial forces that are not related to the ecological, social or amenity value of an actual tree.

Is the answer to plant more trees?

Lewisham council are very good at planting trees, alongside the much-loved local charity ‘Street Trees for Living’. See below a graphic showing the approximate numbers of planted and felled trees over the last decade:

In the last decade approximately 1000 trees have been felled in Lewisham, that’s around 3% if the total, and around 170 of those are due to subsidence. The council points to its record of planting trees, but there is a time lag of about 50 years between a newly-planted sapling and a mature tree in terms of its ability to provide shade, support other species and swallow flood water. We don’t have time to wait for saplings to grow up, we need big trees now. We need to keep alive all those we still have and take care of them.

Here are some examples of how communities have protected their own trees, nationally and locally:

  1. In Sheffield, a Private Finance Initiative signed between the local authority included the felling of 10,000 street trees between 2012 and 2018. Local people organised en masse, were arrested and charged, but finally brokered an agreement with the developers and the council in 2021 to the effect that many trees were spared and the coalition of organisations look after them. A feature film called ‘The Felling’ is being released on this remarkable story in March.
  2. In Cambridge, a row of 100-year-old plane trees in Alexandra Gardens were threatened with severe pollarding due to subsidence. The council were threatened with a bill of £13000 to underpin neighbouring houses, by their insurers. The community have rebelled, see more here:
  3. Closer to home, in Moremead Road SE6 (near Bell Green) two 170 year old oaks are threatened with felling due to subsidence. The evidence that they are causing subsidence has never been made available and it is thought to be the mere threat of litigation by insurance companies that have driven the council to repeatedly try and fell the trees. They have not yet succeeded due to the determination of the local community (which Climate Action Lewisham has supported). There are ropes in the trees ready for tree-climbing protesters to shin up among the branches at a moments’ notice, but the actual ownership of the land and the trees is now under question, hence a lull in the threat to the trees.
  4. In Senlac Road, the last plane tree in the whole street is under threat due to subsidence in one property. The owners of the property are distressed by the cracks in their walls, understandably. All the other neighbouring homes are underpinned and have never had problems, but the insurers will not contemplate paying for repairs to the house or expensive underpinning, they are consistently demanding the felling of the last plane tree in the street.


If homeowners pay for insurance year after year, at what point are the trees enemies of their homes’ integrity rather than manageable assets? Why are the obvious benefits of mature trees ignored over the risks they pose to buildings through their roots?

Who wins and who loses through the common practice of felling mature trees?
  • Local authorities lose – they have to pay for the felling, deal with the distress and at times expense of local communities and their (increasing) protests, and the down-the-line effects of urban heating, potential flood damage and declining urban wildlife habitats.
  • Local communities also lose – they have fewer birds, fewer insects that pollinate their gardens, their risk of overheating in summer increases, which for the vulnerable is a serious problem. They lose the aesthetic value of the trees and they also lose comparative financial values on their homes.
  • Nature loses: fewer habitats in already habitat-stressed areas does not help birds and bugs reproduce and exist healthily, enriching the biodiversity of the urban landscape.
  • Homeowners with worrying cracks in their property win if felling a neighbouring tree resolves that problem, but they can also be at risk from the issues outlined above, and indeed tree felling may not solve a subsidence problem. Indeed, what is home insurance for? You pay for protection to your home, and there are ways in which homes can be supported and managed, usually expensively, to avoid subsidence caused by soil changes or trees.
  • Insurance companies demand the felling of trees at councils’ expense and refuse to contemplate paying for underpinning or other remedial work that could keep valuable trees alive while ensuring the safety of buildings. Their profit grow while the under-monetised realms of public feeling and nature lose, and those they underwrite do not necessarily benefit in the intended way.

At Climate Action Lewisham we would like to see an end to the common practice of felling mature trees, and to see a policy that would see them protected in all cases, save when they were a danger to life. We would like communities and the local authority to work together with homeowners to find ways to protect property and trees, without putting undue pressure or risk on the council’s slender budget. We feel that a wholesale policy change is needed to bring about this progress, and this is beyond Lewisham council or any particular community’s remit to achieve, but by raising the issue and working together, we believe we can build a pathway to future change. In the meantime the chainsaws are quiet and the remaining birds are building nests.