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Home -> Management & Conservation -> Beech pollards at Burnham Beeches (City of London)
Written by Helen Read   
Thursday, 25 August 2011 09:10
(pdf version of this article at this link)

Introduction to Burnham Beeches

Burnham Beeches is a Natura 2000 nature reserve just 220ha in size, in southern England and 40km west of London. It is owned and managed by the City of London who bought it in 1880 for the people of London.

Today it is managed for public access (and receives over 0.5million visits per year) and for nature conservation. The reason for its European status is the ancient beech and oak pollards that host a range of saproxylic species of invertebrate; some 60 Red Data Book species have so far been recorded. Burnham Beeches is an example of a ‘wooded common’ an area where local people were able to collect wood, cutting it from the trees, and also graze their animals under the trees. It is believed that there were once nearly 3,000 of the pollarded trees and that they were cut to provide fuel wood for the local people. Today there are just over 450 old pollards left, most are beech (Fagus sylvaticus) but there are also a few oak (both Quercus robur and Q. petraea). In recent years there has been a great deal of work carried out on these trees and the land around them.

The importance of the old pollards

From 1988 onwards biological surveys of Burnham Beeches were carried out and these confirmed the importance of the area and, in particular the old trees. Work also started on habitat restoration of the heathland and mire systems within the reserve; probably the majority of the ground under the pollarded trees was historically heathland and acid grassland. A complete survey of the trees was carried out and for the first time it was realised that the trees were dying very quickly and something needed doing to save them and provide continuity of habitat for the species dependent upon them. At this time 550 of the old pollards remained alive.

However, many people said that trying to cut these old trees would not be successful, indeed some attempts in the 1960’s resulted in the death of many trees cut.

Experimental work on young pollards

In the late 1980’s some experimental work was carried out on a small area of plantation beeches. The young trees were cut in various ways to create new, young pollards. The lessons learnt from this were then applied to some of the older trees. Two key aspects were learnt from young pollard creation.

First, that removing all the branches from the trees when cutting almost certainly killed them. Just one tree survived this treatment and the single branch that subsequently grew has always remained tiny, with a single narrow connection down the trunk from the branch to the roots. Secondly, although beech is a shade tolerant tree, these newly cut trees did not thrive if they were in the shade.

Cutting the old pollards

In the early 1990’s small numbers of the old beech pollards were cut, using the principles acquired from the creation of the young pollards. The majority of the old trees were standing in dense shade from birch and holly that had grown up since the early 19th century due to the cessation of grazing by livestock. This secondary woodland needed to be cleared from around the trees to give them enough light. Then some of the large branches were cut, ideally leaving smaller ones to keep the tree alive. Many of these trees grew well and new shoots did arise, mostly from the retained branches left on the trees at the time of cutting. However there were some problems.

In some areas the clearance work was too vigorous. A sudden change in the microclimate around the trees from shady and humid to open and sunny in the summer months was too much for some, especially the oak pollards. This was probably exacerbated by a series of hot summers at this time. Other people working in Britain and clearing conifer plantations from around old oak pollards were finding the same problems. We now know that it is better to let light into the trees in a series of stages, first create a clearing around the tree, ensuring the canopy is not touched by any others, then to come back a few years later and make the clearing a little bigger.

The other problem was getting the balance right between the amount of canopy removed and that left. The trees were falling over and falling apart because of the heavy weight on their fragile trunks. Many were also very tall, the branches having been drawn up to ensure the leaves could get sufficient light, so they caught the wind easily, especially once a small clearing had been created around them. Some of the earlier cut trees had a bit too much canopy removed and, especially where they were in quite shady conditions, they did not grow well. Some trees in very poor health were also cut and these did not respond well either.

Over time the cutting techniques have been modified and adapted. First cuts on these trees now remove approximately 25-30% of the canopy (initially it was probably around 50% initially). The trees have always been cut with chainsaws but some have been climbed and some cut using access platforms. Today a mixture of these two methods of getting into the crown is used depending on the location of the tree and its condition. Modern access platforms enable the vehicle to stand well away from the roots of the trees and reach right into the canopy, they are also low impact and stable to work from.






Current situation
All the old pollards were surveyed again in 2006-7, their condition assessed and individual management plans written for the next 10 years. At this stage there were just 423 of the old trees left.

Today, in 2011 all the old pollards have been worked on at least once. This may not involve cutting the tree; it might just have been given more light or had other remedial treatment like propping a leaning trunk or applying mulch to the roots. Each year the work programme is followed and approximately 50 trees are worked on. Any further clearance is carried out and the trees cut if required. Every second year all the trees are visited to check for any emergency work that is needed.











We are now in the process of making the second cuts on the trees and these are variable, just like the first cuts. The growth from the first cut is examined to see how the tree has responded and the tree shape assessed. The eventual aim is to try and reduce the height of the tree canopy to as close to the original pollard bolling as possible. This always requires several stages and in some cases it is estimated that this could be as many as six cuts. The shape of some trees is such that it is unlikely that this will ever be achieved, the best we can hope for is a stable tree that is as low as possible.

Creating a new generation of pollards

These old trees will not live forever, despite the care and attention lavished on them. It is therefore essential that continuity of habitat (and landscape value) is achieved by starting a new generation of pollards. The initial plantation area has been extended and new pollards created in the course of other work. Some can be made when the clearance work is carried out around the old pollards, some when heathland restoration is done and some (slightly larger) trees have been cut around a car park that would have become safety issues in the long term. The aim is for 1,000 of these replacement trees in total; there are currently over 850.

These young pollards are currently cut on a 10 year regular rotation. Initially the work programme aimed to cut these at the ideal time for the individual tree but the logistics of finding scattered small trees was just too time consuming. Now the area is divided into blocks and one of which is cut each year and this compromise is generally working well. The young trees are mostly cut in the summer months because it was too difficult to cut both young and old trees in the winter for logistical reasons. Generally this works well but there have been problems with oak mildew and this may be exacerbated because of summer cutting.

The annual work programme is:

June - July: Bat surveys* of old trees to be cut (looking for maternity roosts).

July - August: Cutting of young pollards, trees cut on a 10 year cycle.

October - December: Preparation work on old trees. Any required clearance including ‘high clearance’ to ensure the trees get enough light; as the pollarded canopies get lower, the halo needs to be bigger.

January - March: Reduction cutting work on old pollards, typically 10 - 25% reduction.

*All bats are protected in Britain and it is necessary to ensure that they and their roosts are not harmed by the work on the old trees. These trees provide valuable roost sites so the long term survival of the trees is important for the bats, but it is important to know which trees they are using and to avoid harm to them. Bat surveys are initially carried out using a remote Anabat detector in the trees, this is followed up by visual surveys if a roost is suspected.

Evaluation of the work

The restoration work on the old trees has been evaluated and the responses of the trees examine in detail. The annual mortality rate has slowed for the beech pollards from 1.91% prior to 1999 to 1.69%. However it is estimated that it needs to still further to 1.3% per year or less. If this situation does not improve by 2080 there will be less than 100 of the ancient pollarded beech trees remaining. In the course of evaluation the importance of leaving long stubs has been shown. General arboricultural techniques target prune and leave no stubs when the branches are cut. Beech pollards clearly produce more new shoots after cutting if they have stubs of ideally at least 0.5m left between the point of cutting and the first retained branch. For more information about the detailed responses see Read et al. (2010).










For more details about the pollarding work in Burnham Beeches see:

City of London website (for copies of the reserve management plan and publications and fact sheets for the general public): www.cityoflondon.gov.uk/burnham

Published papers about the work include:

Read, H.J., Wheater, C.P., Forbes, V. & Young, J. (2010). The current status of ancient beech trees at Burnham Beeches and evaluation of recent restoration techniques. Quarterly Journal of Forestry 104 (2): 109-120.

For more information about the management of ancient trees and pollards see:

Ancient Tree Forum: www.ancient-tree-forum.org.uk

Natural England publications for example ‘Veteran Trees: a guide to good management. Search for veteran trees on the following website: http://naturalengland.etraderstores.com/NaturalEnglandShop/Search.aspx

 

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