Casebook of Dr. Slater - No. 10 - Death & Resurrection

People don’t like to talk about death – and that’s more than understandable. The death of a friend or relative is a deep loss: your own death can seem like it will involve the loss of everything you know. However, it’s healthier to discuss death on a regular basis – to normalise it and not be so traumatised by it. Death is part of life, as they say – and it is all around us.

For this casebook entry, I’ve chosen a few examples of my ‘Trees Over Time’ images that illustrate different aspects of the theme ‘death’, when it comes to trees. I have a lot of images to choose from on this theme – many showing the space left when a tree is cut down. Perhaps you could argue that the chainsaw is a merciful and humane way to take the life of a sickly tree: quick and relatively painless. I’m not so sure: trees seem to have an innate desire to continue to live, whatever their adverse circumstances: they are some of the real ‘triers’ in life…

 Figure 1

UNSPEAKABLE LOSS

The death or removal of a tree may have few consequences, or many. What the tree is, its age, size and setting, are all key factors in whether we come to care – whether we come to miss the tree as a feature of the landscape, as a companion in our lives. For instance, I do a lot of thinning and coppicing of woodland: I don’t regret all the ‘tree killing’ those processes involve, as, overall, it brings more life to the woodland. At the other end of the spectrum is the loss of very prominent veteran trees that were part of the countryside for centuries – of course, they will be missed. 

Figure 1 shows the major visual impact that two veteran ash trees (Fraxinus excelsior L.) had on the road to Caton, Lancashire: particularly as they have now been removed, so one can contrast the two views of the landscape. Both trees had hollow stems, which I suspect was the reason for their removal. Having looked at them myself about five years before, I could see nothing in their structure that justified their removal, and the risks they represented to person or property was low, as they were established quite a distance from the road. What they were, really, was great (and rare) habitat… Now destroyed. 

In the last decade, both of my parents have died. There are no words that can convey such a loss: I find you come to different realisations about the lives and the deaths of close relations day-by-day – a long interlinked set of epiphanies and memories, if you like. In a similar way, I don’t really need to express in words what this image shows as to what the landscape has lost by the felling of these two ashes. This image can only impact upon you in a way that is meaningful to you: and, if you look at it again on a different day, other thoughts will probably be prompted. The loss of a landscape feature is multi-faceted: it takes a while to figure it all out. 

Figure 2

 DEATH CAN BE LEAF-CURLING

 One cause of tree death is disease, of course. However, it’s rarely as straight-forward as that a tree gets a disease and then it dies. Many disease agents have co-evolved with their hosts, being reliant upon the trees for their own lives, and thus tend to stay at the sub-lethal level. In addition, a tree has many defences and tactics to resist the average pathogen that turns up to cause trouble, generating tiers of defences at the chemical, cellular and growth unit level. Consequently, it’s more common for a tree with underlying stresses to succumb to disease, as its resources for its own defence are diminished. 

There are two major factors to add to that brief account: i) we repeatedly keep releasing, through global trade and movement of both plants and growing media, novel diseases onto trees that have not co-evolve with them: the results of which are often devastating and ii) some trees are planted outside of their biome: if moved to a new country without their associated pests and diseases, such ‘transplants’ may grow well for many decades: if the pests and diseases eventually do arrive, the stresses of growing outside of their biome become evident and the microbes shout “Gotcha!” 

As an example of the latter (wrong biome), the North West of England does not have a climate that suits the growth of almond trees: it’s not Spain, Italy, Iran nor California, which provide most of the world’s almond crops. When it is too damp, the disease that tends to have the most impact is peach leaf curl (Taphrina deformans) which can cause severe and repeated defoliation, slowly debilitating an almond tree. Such an example of a slow, cruel and lingering death by disease can be seen in Figure 2, with an almond grown as a street tree in Cheshire. 

Recently, needle diseases of cedar have come into Lancashire (esp. Sirococcus tsugae): when you think about it, the biome of cedar trees is dry and hot, with Cedrus species coming mostly from Turkey and the Middle East. Diseases are often part of what set the latitudinal limits on where a tree species can grow, becoming much more frequently lethal when the tree does not fit the biome or location it is planted within. Many cedars have died locally, now these diseases have caught up with these transplanted (and arguably mis-placed) trees. 

Figure 3

KILLED BY DESIGN

 Trees are often characterised as kindly, giving organisms that provide us with many benefits; However, it is better to see the fuller picture. All life involves the use of resources that others could be using: most life on Earth relies on the death of others, directly or indirectly. So, it shouldn’t be a surprise that trees kill off other plants through their competitiveness and their own chemical exudates (i.e. allelopathy). It is important knowledge for the garden designer, landscape architect and urban forester, as they need to plan for co-compatibility in their planting designs. 

Having visited many botanical gardens, there is a tendency for some arboreta to become ‘stuffed full’ with tree specimens with insufficient thought as to the space they will require to mature. It’s understandable – it’s the ‘chocolate box effect’: when you are setting up a collection of trees, you’ll start picking out the ones that you want in that collection – and it gets hard to resist having one more – then another one… and so on. Soon, there isn’t the space to display these lovely and rare trees as they should be displayed: a failure in design – and it leads to the loss of some trees because of the shade of others. 

This can be seen in Figure 3: Here, in a well-managed tree collection in a public park, this specimen of silver weeping pear (Pyrus salicifolia ‘Pendula’) was established too close to two larger-growing shade trees: a Père David’s maple (Acer davidii) and a handkerchief tree (Davidia involucrata). As a tree that needs direct light to its foliage, this silver pear was destined to die, just from the position it was placed in this design. For small-growing ornamental trees that are not shade tolerant, a very generous allowance of space should be given, if you want their full effect and good longevity. 

Figure 4

DEATH MAKES WAY FOR NEW LIFE

Arboricultural practice has come on such a long way from when I entered it in the 1980s. As well as the admirable development of better safety for arborists through instruction, legislation, improved equipment and PPE, we have come a long way in incorporating actions of wildlife conservation into our work. 

A tree’s structure is built mostly from photosynthates with some additions of minerals. In other words, a tree can be considered as a large ‘candy stick’ – only that this ‘candy’ is somewhat tainted by bitter and distasteful chemicals and salts – and, if you were to try to eat it, it would be hard to chew and very fibrous! Nature has developed many organisms that can, however, gain the carbohydrates back from eating the bark and wood of a tree – so a dead or dying tree rapidly becomes a succession of ‘feasts’ for a large series of xylophagous (wood-liking) species. 

Figure 4 shows the slow disintegration of the branch work of a dead copper beech tree (Fagus sylvatica ‘Purpurea’). Smaller twigs and branches have been lost first, as they have become brittle from white rot fungi that quickly degraded their strength. At the base of the trunk of the tree, four different macro-fungi are evident, namely smokey bracket (Bjerkeranda adusta), southern bracket (Ganoderma australe), brittle cinder (Kretzschmaria deusta) and oyster mushroom (Pleurotus ostreatus). There are bore holes into the tree in various places and snails are living under the detaching bark. It’s also a popular perching point for local birds. 

Despite arboriculture’s greater recognition of the value of deadwood, there is still, in my experience, far too much of a ‘tidying up’ approach to the management of trees like this one. We need to spend more time with the cutting-edge conservationists who are pushing the ‘re-wilding’ agenda: Nature needs more wilderness to come back in our landscapes – and each dead tree is, ironically, an opportunity for much new life. 

Figure 5

THERE’S A SUCKER BORN EVERY MINUTE

According to the Bible (Psalms 90:10) “The days of our years are threescore years and ten; and if by reason of strength they be fourscore years, it is accompanied by labour and sorrow.” Despite, over the last century, our improving living conditions and more science-based medical care, humans in the UK only have a life expectancy average of 86-88 years: not much more than that observation from two millennia before. 

Although some tree species also share with us a finite lifespan – the lifespan of a typical pine tree, for instance, being quite predictable, some trees have the innate ability to live forever. How do they come to be immortal? 

First, it is good to lay down many dormant buds in your woody structure, if you are planning your own resurrection. This means that when the main stem of an elm or sweet chestnut collapses, new life can come back via the growth of basal shoots. We once scheduled the removal of a mature common lime tree, ground out its stump, and it still grew back. We ground it out further and applied a stump killer but basal shoots still proliferated. This was a lime tree that didn’t want to die! 

Second, the more reliable mechanism for tree renewal, is to have a system of regeneration of shoots not limited to your stump’s base but from all your root system. Suckering, the process of producing new upright shoots from a woody root system, allows a tree or shrub to grow on an area of land potentially indefinitely, unless there are adverse changes in the growing environment. 

As an example of this, Figure 5 shows a pink-flowering variety of Robinia that, when only a young tree of about four metres in height, died back due to a bleeding canker that formed at the base of its stem. This tree was situated in the ornamental gardens at Myerscough, so the dead tree was cleared away. My revisit shows, though, that this tree is far from dead: it has produced about thirty suckers that are thriving (and I’m not sure how many have been cut down by the sit-on mower too!). Some trees are so capable of this type of ‘resurrection’ that they can become quite a nuisance in the wrong setting. 

Dr. Duncan Slater is a senior lecturer in arboriculture at Myerscough College, Lancashire. He is a current candidate for an MSc in Environmental Planning, furthering his education in forestry, philosophy, arboriculture and plant biomechanics to now include ecology.

*** THIS ARTICLE FIRST APPEARED IN THE 2020 SPRING EDITION OF PRO-ARB MAGAZINE ***