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Before the Court of Appeal’s decision in Berent v Family Mosaic Housing and Ors [2012, EWCA Civ 961], it was commonly accepted in subsidence claims that, in order to establish the foreseeability of subsidence,  a claimant simply had to show evidence of a large tree close to an old property, founded on shrinkable soil. As is by now well known, in Berent, the Court of Appeal concluded that this was not enough. In that case, the court developed the prevailing wisdom of earlier cases such as Kirk v Brent London Borough [2005, All ER (D) 130] and concluded that in order to establish foreseeability of harm – and therefore a duty to take any precautionary step in maintaining their tree – the claimant had to prove that there was “a real risk” of damage.

Negligence and nuisance in subsidence claims

Since Berent, it has been clear that there are no special principles of law applicable to claims for subsidence damage caused by tree roots: those subsidence claims are subject to the general law of negligence and nuisance. The Court of Appeal in Berent restated the cardinals of foreseeability; it did not, however, reset them.

To establish liability, the successful claimant had to show not only that a real risk of subsidence damage caused by their tree was foreseeable to the defendant, but also that there were reasonable steps that the defendant should have taken to prevent that damage.

However, in the recent first instance decision in Pattichis v London Borough of Enfield [unreported], when applying the general law to a given set of facts, some of the factors the court considered when assessing the presence of ‘real risk’ were very specific: not only to tree root subsidence cases but also to the individual tree involved. This is a line of reasoning likely to have serious and not necessarily intended consequences for both parties, if reproduced in future cases.

Subsidence damage

The Borough of Enfield owned a Norway maple situated outside the claimant’s property. It was well established and in fact it was agreed between the parties that the tree had caused subsidence damage to the property. The defendant also admitted that in the three years preceding this claim, there had been, to their knowledge, 17 subsidence claims in the Enfield borough, all within a two- mile radius of the property.

Reasonably foreseeable damage

Causation was accepted: the issue in dispute was whether this damage was reasonably foreseeable to the defendant. Should Enfield have acted to prevent this subsidence from occurring?

The claimants argued that the tree presented the requisite ‘real risk’ of damage to the property. Experts for both parties agreed that the following factors were present and that these made the risk of subsidence somewhat foreseeable to the defendant:

  • The property’s foundations were unlikely to accord with any building guidelines, because of their age;
  • The property was founded on London Clay, which is known to be a factor in subsidence;
  • The property was within the tree’s likely zone of influence; and
  • The tree was an acer, a species commonly implicated in subsidence claims.

The claimant pointed to these factors and the high number of known previous claims in the local area as evidence that the subsidence damage to the property had been foreseeable to the defendant. Had the defendant implemented a biennial cyclical management plan for the tree, this would have provided the regular maintenance needed to prevent damage from occurring.

The defendant insisted that the risk of subsidence damage to the property posed by the tree was not significant enough to warrant any duty to manage it in this way: in other words, it did not amount to a ‘real risk’ pursuant to the test in Berent.

Subsidence hotspots

The concept of a subsidence ‘hotspot’ had been developed in the earlier case of Berent. The judge in Pattichis concluded that, in order for an area to constitute a hotspot, there first had to be an explanation as to why it presented an elevated risk of subsidence. The claimant argued that the history of 17 previous subsidence claims within a two-mile radius was clear evidence that this was a known area of subsidence risk. The defendant pointed out that the houses within that radius were of different types of construction. A ‘hotspot’ could be more accurately defined in an area where subsidence occurred to a more homogenous group of buildings, such as a particular housing estate.The judge concluded that a history of similar incidents close by was not sufficient in itself to establish a hotspot.In his opinion, the tree in this case posed no more of a subsidence risk than any other Norway maple tree in the defendant’s borough, situated up to six metres away from any other pre-war housing stock, built on London Clay.

Tree management

The age of the tree in 2009 (when the damage occurred) was disputed. However, it was accepted by both parties that it was a relatively young tree. It was approximately nine metres in height at the time of damage and both parties agreed it had the potential to grow to an estimated 18 metres, left unpruned. They also agreed that it was difficult to assert that it would definitely cause subsidence damage to the property at any given time. Nonetheless, the claimant argued, the tree could not be said to pose the same risk as, say, a newly planted maple tree.

As a London borough, the defendant ought reasonably to have known about managing the risk of tree-root subsidence and ought to have been aware of the risk that the tree posed, especially in light of the 17 previous subsidence claims, which they had admitted they knew about. The claimants also highlighted to the court that some Norway Maple trees within the area of the previous subsidence claims and under the control of the defendant were managed according to a programme of more frequent, biennial cyclical pruning. The tree itself was pruned at four year intervals.

The judge considered the two academic papers relied upon by the claimants’ expert: the 2008 third edition of the Risk Limitation Strategy for Tree Root Claims by the London Tree Officers Association (LTOA) and the Horticulture Link 212 Project (Hortlink).  The claimants’ expert argued that, in essence, a biennial 70-90% crown volume pruning strategy (sometimes referred to as ‘crown reduction’) would, according to this research, more than likely have prevented the subsidence damage to the property by restricting moisture uptake from the underlying soil. It was possible to manage that risk without removing the tree, by pruning the tree using the Hortlink method and in a manner adopted elsewhere with such trees throughout London.

The defendant did have a biennial maintenance strategy for minimising the risk of subsidence in the borough. This strategy recognised that acers (the species that includes Norway maples), pose a high risk of subsidence. Norway maples were, however, specifically excluded from the biennial pruning regime and instead were generally maintained on a much more extended four-year regime. Exceptions were made in the case of individual Norway maples, which the defendant had identified as posing a greater risk than average. Other types of acer, however, such as silver maples, were managed on the two-year cycle, as the defendant sought to differentiate between specific trees within species.

Although the defendant accepted maples in general tolerate pruning well, they felt that Norway maples were at greater risk of reacting badly to pruning. The judge seemingly accepted the defendant’s evidence on this point: this was a further reason for omitting it from the more rigorous biennial management scheme.

Amenity of the tree

Neither party denied that trees are an important feature in any landscape. There was no doubt in the judge’s mind that trees fall into a category of potential risks that can be described as being beneficial to the public. The judge, quite properly, considered whether the risk posed by the tree was enough to warrant a higher degree of maintenance and, if so, what aesthetic impact any work to the tree might have on its amenity value.

The Hortlink method of 70-90% pruning became the focus of the argument. It is clear that pollarding a tree can reduce the risk of future subsidence. What seemed to the court to be less certain was whether pruning to the Hortlink standard would prevent future subsidence in the same way. In the end, the judge was unable to move past that uncertainty. He concluded that, by way of interpretation of the LTOA figures, reducing the tree by 70-90% would only reduce the risk of subsidence by 18-20%. In addition, the judge concluded that Hortlink pruning would reduce the tree virtually to a stump, severely reducing its amenity value.

This was not the view of the claimants’ expert. There are several ways to achieve sufficient leaf area reduction while preserving amenity value: a Hortlink 70-90% crown reduction will not inevitably turn a tree into a stump. Nevertheless, the judge felt the amenity value and canopy coverage would be too severely reduced for Hortlink to be considered a proper maintenance option in this case. The claimants’ expert considered this view to be at odds with the adopted management regime of many thousands of London’s street trees and the published advice of the LTOA.

The tree’s amenity value appeared to play a significant part in the judge’s decision. He was reluctant to deliver a judgment whose effect would be to require all trees to be pruned in a manner that would make them appear not dissimilar to stumps.With this in mind and with, in his opinion, no guarantee that pruning to this level would prevent subsidence effectively, the judge concluded that the defendant’s position was the more realistic approach to the risk.

He also acknowledged that the defendant has a limited budget and so can only manage trees posing the highest risk of subsidence. He concluded that the defendant did not breach any duty to the claimant by failing to include the tree in its two-year maintenance cycle.

What happens next?

As often happens, this was certainly a case that was successfully defended on its own facts. Although the decision is one made in the first instance and therefore not binding on any future court, local authority tree owners are likely to feel encouraged by it. However, it was clearly a finely balanced decision that depended upon the interplay of several variables, particularly the specific tree and building involved.

There are, of course, implications for both future claimants and defendants in subsidence claims,. Was the judge in this case suggesting that claimants are bound to consider not only the species of the tree causing the damage and its distance from the affected property, but also trees of similar species in the area, their distance from properties and whether they have also caused subsidence?

Further, if the defendant has considered the species of tree in relation to its subsidence risk at any stage and decided against actively managing the tree, does this exonerate them from all liability – even if the decision not to actively manage is one disputed by the claimant?

It appears that claimants may now have to think more carefully about what information to seek from the defendant at pre-action disclosure stage. A more detailed approach will be necessary if, as appears to be the case, the claimant must assess the reasonableness of the defendant’s tree maintenance regime and considerations in light of published research and government papers.

While this ruling has implications for claimants, largely around pursuit of the claim pre-issue, it should also give prospective defendants food for thought. In particular, the individual species of tree that was the cause of the damage was a very significant factor in the judge’s decision. Looking more closely at that tree, one wonders for how long the choices made by the defendant would have continued to be sufficient to satisfy their duty of care. At the time of the claim, the tree had reached a height of nine metres. It was agreed that it would likely grow to a height of 18 metres. At what point would it have become unacceptable for the defendant to do nothing further? At what point should the tree have been put on a more frequent and proactive maintenance regime? Those questions remain unanswered.

Unfortunately, trees do not behave with absolute predictability, unless they are felled. The reluctance to do this, sacrificing their amenity value, appears to suggest that the claimant will almost always fail on this point. Would the judge’s decision have been different if the tree had been less visible to the public? If there were a significant number of similar trees within a small area, would this have offset any adverse aesthetic impact of heavy pruning? Clearly, if the court had been persuaded that the tree would have responded well to pruning, that might have produced a different result. If the other trees on the same street had been of a different species that tolerated pruning well, could or should this particular tree have been removed? If the trees implicated in those 17 previous subsidence cases nearby had all been silver maples, would that have increased the perception of ‘real risk’?

Unfortunately, in finding for the defendant on this occasion, the judge may inadvertently have increased the burden on all defendant local authorities in future cases. It seems that it may now be necessary to examine each case by reference not only to the tree causing the damage but the trees in the surrounding area. This of course will also mean scrutinising the local authority’s strategy not only for that tree but also for the area. Success in future will depend on the defendant’s ability to justify their overall strategy of tree management in their boroughs, as well as their specific maintenance strategy for any individual tree within it. Since a tree does not stand still, defendant local authorities will have to point to a strategy for each tree that evolves as it grows, if they are to escape liability.

As the definition of a ‘hotspot’ also continues to evolve, local authorities may find themselves in the unenviable position of also having to dispute every previous case of subsidence in the surrounding area, in order to defend the claim in hand. If this case has set the bar higher for claimants, future defendants may expect to receive more frequent and more extensive FOI requests, backed by Pre-Action Disclosure applications at an early stage and more and more extensive Requests for Further Information, post-issue. Although not binding, if this decision is an indicator of a future trend in tree root subsidence litigation, then successful cases will become ever-more fact specific, increasing the burden on local authorities to give early disclosure. The role – and the cost – of the arboricultural expert in isolating the real risk in any particular set of facts will also increase significantly.  If this decision marks the beginning of a trend, local authorities may yet see individual subsidence claims fought tree by tree, and street by street in future.

For more information on tree-root subsidence claims or any of the other issues raised in this article please contact Natalie Blannin in our Property Insurance Litigation team at [email protected]/0117 394 5048