CASEBOOK OF DR. SLATER - No. 21 - Veteran Trees

Respect For The Elderly?

The management of older trees is a massive subject, so this short article can only touch upon this topic. I’ve themed it around ‘respect’, as I think that’s a good starting point.?

First, some basic definitions:?

Mature tree: this is usually taken to be a tree that has completed a previous period of rapid growth and has now reached a height and girth that will only change slowly from now on. We often gauge tree age by tree size, assuming that only a large tree for its species is a mature tree, although there can be exceptions. We do not apply a rule that when a tree is sexually mature that it is a ‘mature tree’, as this varies a great deal by species (e.g., for a silver birch, it can be as little as three years from germination before young birch trees start producing seeds themselves, although they are not yet 2 metres tall!).?

Veteran tree: this is a mature or older tree that has gone through stages of damage and decay, resulting in a structure that is unique and typically of higher ecological value. Veteran features include storm-damaged branches, large diameter deadwood, decayed sections, branch and stem cavities, splits and previous partial collapse.?

Definitions of what is a ‘veteran tree’ vary (Read, 2000) – it is a somewhat subjective assessment. There is a general expectation that a veteran tree will have a very large stem girth, but that’s not at all necessary for a tree to fulfil the basic criteria of some definitions – an older tree that has gone through substantial physical trauma. Thus the term ‘veteran’ is very appropriate, as when we consider a (human) war veteran, we appreciate the many traumatic situations they will have gone through – and the altered structures of veteran trees come about from both decay and disaster, the trees having to just stand there and put up with whatever comes.?

In some schemas, there is a tree age category that lies between ‘mature’ and ‘veteran’ – which is termed ‘over mature’. However, for amenity trees, this is a wholly unacceptable category, in my professional opinion, as the term implies to other people that the tree is “too old” and thus should not be kept. An amenity tree cannot be too old – it’s structure may deteriorate such that we have to take remedial action or remove it, but it’s totally daft to have a “too old tree” category lying between ‘mature tree’ and ‘veteran tree’. Our industry’s documents, guidelines and standards should be changed to prevent this derogatory, ageist term being used – age alone should not be associated with a lower value – it should, in fact, be quite the opposite for trees, as it is for fine wines and cheeses – greater age should engender greater respect. With age comes many values – in the case of trees, mature and veteran trees have a strong presence in the places where they grow, making those places special, of historic interest, different from anywhere else.?

Mature, old and veteran trees often require greater care in their management, as their growth rates are low and they have got accustomed (in science: ‘acclimated’) to the site in which they are growing.?

Routes to becoming a veteran?

Decay is an integral part of the life cycle of a tree – it will inevitably occur to all temperate and tropical trees, and, if the tree is mostly undamaged, such decay will normally start in the tree’s root plate and the centre of the tree’s stem, as older roots decline and die right underneath where the tree’s trunk is situated. If the decay’s process is slow and the tree is relatively healthy, the stem will often produce a bulge around the decaying region of its lower stem. This decay-and-bulge process can result in hollow trees in oak and sweet chestnut of very large girth, of which England holds the greatest number of any country in Europe (Read, 2000). The first image shows such a veteran oak tree, situated in parkland at Ripley Castle, Yorkshire. Cattle damage to the base of the tree and its roots, through trampling, poaching and compaction will also have had a role to play in the current form of this tree: unfortunately, if cattle density is too high, such parkland trees can be killed relatively quickly, as I have seen many times.?

Storms can rip limbs off trees, leaving gaps in their canopy and wounds that may lead to internal decay and cavities over time. Many of our native tree species are really resilient to such damage (almost as if it was quite windy in the UK!) and often cope with limb loss, and, exhibiting their wounds, continue on. In this second image, a mature oak in parkland has suffered a limb failure (circled in red) and then re-sprouted extensively around this wound, filling in the gap in its crown. The associated wound will cause some decay in that part of the tree – but it was not a fatal wounding by any means.?

There are means and methods to manage high value amenity trees that start to break down due to damage and decay. My third example is the famous ‘Allerton Oak’, which lies within Calderstones Park. Liverpool. This tree, protected from the public by iron railings, has had multiple metal props fitted to it, ensuring it does not fall apart completely. My time-lapse over eleven years represents only about 1% of this tree’s lifespan so far – which is very humbling. This tree is so highly respected by locals that it won England’s ‘Tree of The Year’ award in 2019.?

Some of my favourite trees are those that have slumped over onto the ground and are, essentially, having a long rest. What results is a reclined stem and many limbs heading up vertically along the tree – which is why they get to be called ‘harp trees’, due to the upright new limbs looking like the strings of a harp (particularly when aligned along a straight trunk that has fallen). This beech that has become a harp tree at Arnside Knott, which is a site local to me. Although only a relatively ‘young’ mature tree, it has great potential to make a very special tree into the future: it has already rooted in multiple places and produced over twenty stems, creating a low dome on this steep coastal hill. Fallen living trees should be respected, if there is scope to retain them (most often in parks and woodlands), as they can persist for centuries in this prone position.?

Threats to our older trees?

Climate change is an existential threat to nearly all forms of life on Earth – and trees are no exception (Williams & Dumroese, 2013). Indeed, mature and veteran trees will often prove more vulnerable to the changing climate, despite having lived a long time, because of their more limited ability to respond to such changes.?

Climate change can directly cause stress to our tree species, but it also increases the likelihood of attacks by some of our extant pests and diseases (e.g., Cryptostroma, Phytophthora). Our trees also have to contend with new pests and diseases that can come in through global trade (particularly in the ‘dunnage’ – or wood packaging - of overseas consignments). Other pests and pathogens outbreak somewhere else in Europe and then spread to our shores a few years after that initial ‘touch down’ in our part of the globe.?

Our ash trees, in particular, are currently being damaged by ash dieback disease (causal agent: Hymenoscyphus fraxineus) and are also threatened by emerald ash borer (EAB) (Agrilus planipennis), which is travelling west from eastern Europe, and is very likely to reach us in the foreseeable future. This ‘double-whammy’ will prove devastating to our ash trees, young and old, having personally seen how much death and destruction EAB has wrought in the northern United States and Canada. Veteran ash pollards in Cumbria are already declining in number because of ash dieback disease. Locally to me there is a very large-girth ash pollard in a local village – presumably an old hedgerow tree that was integrated into the street scene. It would be quite a loss to see this old tree go – but that seems inevitable because of these species-specific threats. ?

Another major cause of mature and veteran tree loss is through human activity. Deliberate damage, removal and vandalism is not that common, but death and decline are often caused by ignorant actions, neglect or site changes. Rather than our ignorance or our neglect, old trees need our respect – and sufficient space given over to them. Perhaps because older trees are so numerous in England, they often get treated poorly, as if they were a low value commodity. The pictured mature alder (Alnus glutinosa) has been used as a fence post by a local farmer: the nails hammered into the already decayed trunk will not help with the tree’s longevity, nor allowing sheep or cattle to step right on the tree’s rootplate.?

Lesson Learnt?

Old and veteran trees are very valuable: especially, we cannot plant them nor replace them in our own lifetimes. We only get to ‘inherit’ the trees that were planted or self-seeded centuries before, and which survived. England, in particular, has a fantastic inheritance of old trees – but the ingress of pests and diseases, the vicissitudes of climate change, and how we treat such trees means that this population may diminish if we do not give them due care, attention and respect.

References?

Lonsdale, D. (ed.) 2013. Ancient and other veteran trees: further guidance on management. London: The Tree Council.

Read, H.J., 2000.?Veteran trees: a guide to good management. London: English Nature.?

Williams, M.I. and Dumroese, R.K., 2013. Preparing for climate change: forestry and assisted migration.?Journal of Forestry,?111(4), pp.287-297.

About the Author?

Dr. Duncan Slater is a senior lecturer in arboriculture at Myerscough College, Lancashire. He is also a co-ordinator of Arbor Day UK (#ArborDayUK) – an action group that seeks to put new trees and woodlands back into the landscape. One day, at least one of the trees planted by Arbor Day UK will become a veteran tree – and it’s going to be worth the wait!

*** THIS ARTICLE FIRST APPEARED IN PRO ARB MAGAZINE, SUMMER 2022 ***