Reasons for the pollarding of willow tree on Stamford Meadows
The pollarding of a willow tree on Stamford Meadows has been causing a stir, with many residents feeling it should not have been done. Brett Redshaw, the owner of Stamford-based Woodcraft Tree Services Ltd, has responded to the criticism with details of why the work was carried out - and why now...
We recently carried out the re-pollard of the large willow tree on the meadows and it has been wonderful to see the depth of feeling that has arisen as a consequence of that work.
It is amazing that so many local people have a feeling of affinity for the willow, it heartens me to know that trees continue to provide a feeling of shelter and community as they have done for thousands of years.
I wanted to explain the reasons for the work, to counter some of the misinformation that seems arise at times like this.
The work carried out was a re-pollard, not a prune, not a reduction, and certainly not a ‘topping’. Pollarding has been carried out for over 2000 years and can be carried out for a number of reasons. In this case, a pollarding cycle was initiated decades ago to maintain an appropriate height of the willow, and to increase its healthy lifespan.
Although this can, at first hearing, seem counter-intuitive it is crucial to understand that tree physiology is unique. Their cell structure and mass-flow systems are different to all other plants, and their reaction to wounding far more complex.
Below are the key points (this is the tip of the iceberg in terms of an explanation of tree physiology and response to stimuli):
Limiting limb length reduces the chance of storm damage.
Pollarding lowers the centre of gravity of the tree and greatly reduces the turning force which can be leveraged at branch unions and at the base of the tree, therefore greatly reducing the chance of significant damage caused by wind sheer or torsional force.
Pollarding changes the ratio of kinetic to static timber.
Static timber consumes but does not make energy, kinetic timber produces energy via photosynthesis. In most trees this kinetic timber is exclusively young shoots and leaves. As a tree ages more of its mass consists of static timber and its energy consumption increases relative to its energy production. Pollarding removes static timber which is then replaced by vigorous new growth. In this way it keeps the energy ratio closer to that of a much younger tree.
Pollarding, when carried out over an appropriate cycle, extends tree life.
For the physiological and mechanical reasons explained above, a tree which has had a pollard cycle initiated at an appropriate phase of life, will outlive a tree of the same species which has never been pollarded. Most old trees die from compound factors, with oak trees being the classic example of this. The leading cause of oak tree death is Chronic Oak Decline, which is a non-specific combination of pests, disease and environmental factors. The best defence for a tree is to have a high level of available energy, combined with sufficient nutrition and water. Pollarding increases the average annual level of energy available. This boosts the defence responses of the tree and make it able to overcome adverse factors which may otherwise prove fatal in combination.
The other point to address is the timing of the work. There is no hard and fast rule about when trees should be pollarded, rather there are a number of factors which must be taken into account. So I will explain why the work was carried out now.
Energy levels within a tree fluctuate during the year.
The spring is a time of high energy expenditure, cutting away new foliage as soon as it grows would give the tree no chance to renew its energy levels. Summer is a time of high energy availability, long bright days, and so new foliage will produce a high energy return. Autumn is too late and too early, the tree will try to regrow lost canopy thereby expending energy, whilst the days grow shorter and darker, limiting the energy which can be recouped by the tree. Winter can be an excellent time to pollard as the tree is dormant so no active canopy is lost, however the tree is unable to compartmentalise the wounds as efficiently due to dormancy, and there is a risk of frost damage to exposed cambium.
Fungal spore count.
Open wounds in trees bypass the trees natural defences against fungal ingress. Pollarding a tree in autumn when the fungal spore count is at its highest gives the greatest chance of those wounds being exploited as an entry point for wood-decaying fungi. These can dramatically shorten the life of a tree and also make the tree structurally unsound, sometimes necessitating the need to fell the tree under public safety grounds. In summer the fungal spore count is at its lowest.
A strong factor against pollarding in summer is compound stress caused by wounding the tree at a point of water stress. In the case of the meadows willow the soil around the roots is kept moist by lateral water flow from the river on either side.
I hope that this explanation not only reassures people about the willow on the meadows in particular, but also goes some way to reassuring people that these decisions are taken with the wellbeing and longevity of the tree in mind. We are a skilled and knowledgeable profession. We do not simply ‘hack’ trees as the whim takes us.
If you ever see myself or my team carrying out work we would be happy to explain to you the reasons behind the work and the techniques that we use. I would welcome more people with a genuine interest in tree physiology. They are truly fascinating organisms and there are so many basic misconceptions which abound. I am happy to talk about trees all day with anyone motivated enough to listen and learn.