Article: Veteran trees, extreme weather and habitat benefits Looking back on October 1987

With the 30th anniversary of the hurricane approaching and having visited many sites with old trees both here and abroad over the last 10 years, I have been moved to ponder how many veteran/ancient trees were perhaps lost to us in the UK on that fateful night in 1987. The great storm brought gusts of up to 94mph across London, leading to 15 million trees being damaged and/or destroyed throughout the UK and 18 people losing their lives. Six of the seven eponymous oaks in Sevenoaks were toppled and the National Pinetum at Bedgebury in Kent lost at least 30% of the National Conifer Collection. Having witnessed the ferocity of that tempest during the evening and throughout the night, I returned to work the following morning, weaving my car through the woody debris of the aftermath. I was unsure what to expect once I arrived at the gates of the north London open space of Hampstead Heath where I was based as a horticultural apprentice. Sadly, I was to witness devastation. Observations over 30 years suggest that there are multiple outcomes for veteran trees exposed to severe weather events. We see destruction, dysfunction and decline in the roots, trunks and canopy of old trees. However, we often, with time, also see rejuvenation.

Hampstead Heath storm damage, 1987. 

A total of 647 trees were damaged at Hampstead Heath in October 1987 with 483 of those completely uprooted – and somewhat surprisingly, only four of those were veterans (250 years old or above). I have talked with other tree managers/ officers/ecologists across open-space sites in the south-east of the UK (especially those with large numbers of ancient/ veteran trees), and it turns out that old hollow trees came through the storm largely unscathed.

Most of these sites were extensively surveyed post storm, and thanks to the efforts of those surveyors, we have valuable information about the species and age of trees impacted by the storms. At Hampstead, all the damaged and toppled trees within the site compartments were recorded and measured. The map (below) shows a section of Windsor Great Park which was compiled by Ted Green post storm. It records oak trees lost (red dot), oak canopy damage (red circle), beech trees lost (blue circle), sweet chestnut lost (green triangle), lime trees lost (orange triangle) and various other species. Windsor Great Park lost none of the ancient hollow trees at the roots; only partial canopy and branches above the hollow trunks were affected.

Perhaps there are reasons which can be debated for this, including (natural and unnatural) propping, shorter stout retrenching canopies and protection from the wind by taller younger neighbouring trees, but the hollow nature and flex in movement of these veterans played a fundamental part in their on-going survival. Ted recounted to me one particular old beech at Windsor which was hollow from the ground right up to its canopy framework; it stood firm whilst the younger sweet chestnuts in the plantation around it succumbed to the wind and all fell like dominos. Richmond Park lost none of its famous named veterans/ancients like the 750-year-old Royal Oak. Rangers who were working at Burnham Beeches and Ashtead Common at the time of the storm recall that none of their hollow old pollards collapsed or toppled. The low numbers of veteran trees lost at these five sites amongst the thousands of damaged and uprooted trees strongly suggests that veterans which are hollow and/or retrenched with shorter, compact canopy sails can and do withstand significant storms like the one in 1987.

The following 3 trees are good examples of Ancient/veteran trees that came through the storm largely unscathed.

Above; The Royal Oak, Richmond Park

Above; Pollarded beech, Burnham Beeches

Above; King Offa's Oak, Windsor Great Park

The case studies that follow examine two Hampstead Heath veterans that survived the storm. Both trees have benefited from management intervention.

Case study 1: The Bandstand Oak

In the heart of a north London Victorian park known as Golders Hill sits a well-known landmark tree called the Bandstand Oak (above).

Thousands of people have sat in their deckchairs during the summer months over many decades listening to jazz and watching clowns hosted at the park’s performing stage. The oak tree is thought to be approximately 450 years old and has a girth of 6.75m. I first became aware of this particular tree as a child when my family visited the park and Hampstead Heath around the late ’70s and early ’80s. The two images (below) taken in 1900 and 1975 appear to show the tree had been thinned and/ or pruned but they may also reveal what years later I would understand to be early natural retrenchment.

It is an imposing landscape tree that is a relic of a less urban time in the site’s history. It had changed little in terms of aesthetics and health since the beginning of the 1900s up to when the storm struck. I take many images of trees daily, both at work and in my leisure time, so it is a little frustrating that I didn’t capture any images of this tree in the immediate aftermath of the storm. We didn’t have digital cameras back then and were too busy clearing up damaged trees across the site and unblocking the roads outside. The tree is open-grown and sits on a hill so the wind had complete access to wreak havoc on the canopy. I suspect that the oak was then, as now, colonised by the brown rot decay of the chicken of the woods (Laetiporus sulphureus) and this would have had a significant influence on the oak being dismantled branch by branch as opposed to being completely uprooted. The ferocity of that storm and the heartwood decay resulted in the upper crown becoming smashed and fractured. The crown was subsequently cleaned and made ‘safe’ by being reduced back to almost just the trunk and stubbed main scaffolds. At that time, the knowledge of retaining as much photosynthetic material as possible whilst reducing a veteran tree (post storm or otherwise) was perhaps in its infancy and the guys on the tree team had a very long list of trees to clear up.

Above; Bandstand Oak 1975

Although the 2 images of the tree out of leaf above were taken several years after the work, the tree’s winter frame allows us to see the severity of the reduction carried out at the time of the storm in comparison to the tree as it was in the earlier photographs. Clearly visible in the sunrise image is how well the tree has responded to the ‘topping’ over that time. The reiterated branch framework has developed well in the last 30 years due to the oak’s vitality.

The only canopy work done in the last 15 years has been to retrieve a succession of lost kites and the removal and/or partial removal of significant-sized dead branches above static park benches. With time and an understanding of the niche habitat that retained dead branches provide for biodiversity, we managed the risk of the sitting target by moving the ‘static’ benches and erecting a metal fence which in keeping with the park’s boundary fencing. This has also had the benefit of stopping young aspiring monkeys who loved to climb the old tree and were damaging the bark and lower branches. Those future potential arborists still have younger trees to climb on as several young oaks were planted before and after the storm to continue the oak population that has been part of the local historic treescape for centuries. The tree does suffer root issues which can be seen in the decline on one side of the canopy. This is due in part to the close-cropped grass-mowing regime and the compaction caused by heavy foot fall – this is a popular, well-used park. The demand for space during good weather and events held at the bandstand limits the total area of roots we can protect with the fencing.

The tree has had on-going applications of foliar microbial compost tea which it is hoped will benefit the health of the oak and the soil below. It remains an imposing landscape feature tree now and hopefully for many decades to come.

Case study 2: The hollow beech

This hollow beech has a girth of 5.52m girth at 2m. It mostly withstood the 1987 storm and also subsequent arson attacks. It has been hollowed out by the activity of bacteria and various decay fungi over the last 100 years or so. The storm stripped bare most of the upper canopy, leaving no upper trunk beyond 13m and only six of the main scaffold branches that make up the remaining framework. Surprisingly for beech, over the next three decades the tree has reiterated a new canopy, forming dozens of new ‘young trees’ on the upper branch surfaces.

The beech is subject to a reduction cycle where it is reduced in height by 1–2m every five years with the intention of keeping the canopy from protruding out beyond its neighbours and having the younger, weakly attached pole regrowth exposed to wind load. (Rare, non black and white image of the author up in the canopy of the hollow beech picture 3 below)

Habitat created by natural and unnatural events

Storms of course are not the only major risk to veteran trees. Although the veteran pollard oaks at Ashtead Common largely survived the great storm of 1987, unlike the maiden beech and other species in the locality that were swept over in their hundreds, many of them succumbed to a large (bracken) fire in 1990 which damaged or destroyed over a hundred of the old pollards. Those trees are no longer alive. However, they still provide valuable habitat as standing dead wood volume for a wide range of saproxylic invertebrates, fungi, bats and birds. Maintaining these standing dead wood volumes is an important aspect of biodiversity management. For more information on this habitat-type creation and retention, see the authors article ‘Standing dead trees in the urban forest’ in the ARB Magazine 166 (autumn 2014).

Storms,

Pruning and other events like mechanical injuries help create veteran features and improve potential habitat value for biodiversity.

As long as assessment of the loss of part of the tree can determine that there is no adverse effect on its stability, these tears, branch socket cavities and impact wounds can be retained as future habitat. The Bandstand Oak has been a regular host to kestrels and to smaller avian species like nuthatch and blue tits. Cavities in the trunk and branch unions from pruning and natural branch tear outs provide fine habitat potential that is utilised by successive generations of birds and bat species. The Moccas Park oak (below) has been left unmanaged because it sits in a very rural landscape with low risk to site visitors whereas the Hampstead oak pictured (which is colonised by Fistulina hepatica) has been lightly reduced to reduce load on its canopy sail as it sits in an urban open space with many visitors.

Above; The Moccas Park Oak

Above; Hampstaed Oak failure. Fistulina hepatica colonisation

Fungi species like Laetiporus sulphureus, Fistulina hepatica and Buglossoporus quercinus are just some of the organisms at play in the slow decay process of wounds ; species like owls eventually take advantage of these sites and colonise them. The decay process can take many decades in temperate areas like northern Europe. Bees, woodpeckers, parakeets and other species all accelerate the process of cleaning out cavities for their own use and future use by larger inhabitants.

I give great thanks to Ted Green who continues to inspire and also helped with information regarding the veteran and ancient trees at Windsor Great Park before and after the great storm.

This article was originally published in the ARB MAgAzIne | Issue 178 Autumn 2017