Leading Arboricultural and Ecological Consultants

Tree MORPHOLOGY & diagnostics

Seminar V

Report on the third Treeworks Environmental Practice/AA Seminar held on 23rd & 24th March 2006

Originally published in essentialARB magazine issue 16 by Andrew Cowen and Neville Fay

As we say goodbye to the last of the autumn colour left on bare winter branches it is time to admire the structural beauty of trees. Beyond this aesthetic interest there is also something special to learn about ageing and morphology in trees. Andrew Cowan & Neville Fay consider some ideas about the ageing process of trees derived from the work of Pierre Raimbault.

Although Raimbault’s idea were first presented in English at the second European congress of Arboriculture in Versailles 1995, they have not gained a broad understanding in Britain. So in response to the view that tree morphology needs wider appreciation in arboricultural circles Treework Environmental Practice will be introducing Raimbault and his morphological studies to a UK audience on March 23-24, 2006 as part of the ‘Innovations in Arboriculture’ seminar series.

Morphology fundamentally relates the form and structure of an organism. In trees the study of morphology has been linked to ageing and the physiological processes associated with different developmental stages.

Tree age classification is a valuable tool for tree recording and monitoring. However, the use of a series of labels (such as ‘young’, ‘middle-aged’, ‘mature’ to ‘over-mature’) as age classification can lead to an oversimplified structural view, while the subjectivity of its use may be prone to inconsistencies and in turn to misconceptions about how trees age.

Where there is poor understanding of the ageing process in trees those involved in surveying and management may build-in inconsistencies in characterising, recording and reporting their condition. This may apply where conclusions are drawn regarding tree condition in the context of observed stresses, particularly if the ageing process is reduced from a dynamic developmental progression to viewing the tree in terms of aged-states, each representing a static condition.

Understanding the ageing process can lead to an enhanced appreciation of the life-cycle of trees and significantly contribute to arboricultural management decisions. Such knowledge takes into consideration tree species’ growth characteristics and applies these to morphological and physiological changes that occur during the developmental stages of the Tree-ageing process.

Tree age is when the germination date is known and can be expressed as a chronological measurement. However this can be deceptive when considered in terms of the ageing developmental process as different species grow and mature at different rates.

Tree growth is influenced by genetic factors and the growth context, to the extent that physiological and morphological processes will determine the increasing complexity of the organism from establishment to maturity. As a result, for example, a stressful growing environment can influence the early developmental (establishment) phase leading to a prematurely ‘aged’ tree, while competition between adjacent trees may prolong the establishment phase, leading to slower, more gradual early-stage changes.

The architectural morphology of trees contributes to their aesthetic appeal. However from an arboricultural viewpoint an understanding of morphological stages can be used as an aid to the observation and diagnosis of stress. Pierre Raimbault’s concept of tree morphology, in viewing the tree in terms of a series of standard developmental stages, studies how morphology operates, and, from such observations, he contends that it is possible to provides a systematic approach to understanding ‘normal’ and ‘abnormal’ development.

This is based on the premise that the physiological and environmental history of the tree is somehow ‘written’ in its form and that variations from a developmental norm may be interpreted as ‘perturbations’ from normal physiological status. In order to make this manageable Raimbault in identifying ten distinct stages in the life-cycle of trees, seeks to show complexity and changes in both the above ground and below-ground architecture of the tree during the passage through these stages.

Thus Raimbault’s system considers a diagnostic approach derived from morphological parameters and compares these with a normative ‘standard’. This allows observations to gauge whether the current state of the tree conforms to the established standard so that the observer is able to place the tree in one of the stages on the standard developmental scale.

On the other hand, if certain observed criteria do not match, then this can direct the arborist to regard the tree’s condition as physiological perturbed. To make informed arboricultural management decision it is therefore important to be familiar with the method for morphologically-based physiological diagnosis to be able to ascribe, understand and interpret causes to these differences.

Raimbault refers to the concept of ‘plant memory’ and idea which dates back to such venerable thinkers as Leonardo da Vinci and Wolfgang Goethe who observed plant and tree morphology, structure and function. He visualises their physical form as a record of their development. Interpreting this ‘memorised’ physiognomy helps to identify both current stresses and traumatic events in the past growth processes of the tree.

Stages 1 to 5 (the first sequence of Raimbault’s ten stages from seed to eventual senility) relate to the development from seedling to early maturity. During these early stages there is progressive branch differentiation and complexity in crown structure in the process of optimising leaf area, while lateral development is suppressed by apical dominance.

The root system also begins to develop a tiered structure optimising its capacity to fulfil the growing demands of the expanding leaf canopy (Fig 1).
During stages 6 through to 8, apical dominance is progressively reduced resulting in an increasingly rounded crown, some loss of peripheral vitality and a gradually progressive loss of under-branch sub-lateral growth (abaxial mortality).

Reiteration (replication of the tree’s form in individual epicormic growths) begins to initiate, and when this coincides with occasional branch loss dysfunctional tissue gradually and increasingly develops from fungal colonisation. This process instigates growth about the inner, lower crown region in response to the declining, retrenching outer crown canopy (basifugal mortality).

Raimbault’s stage 8 is characterised by a corresponding retraction in the root system. Where the oldest roots die off internal fungal decay of the lower trunk may also then occur and introduce decay into the centre of the base of the trunk.

Raimbault considers that some trees will die at stage 8, but there are those that will survive beyond this and progress through the subsequent two stages (9 and 10) and beyond. In stages 9 and 10 he describes how the living crown condenses to form a lower canopy and there is a corresponding retrenchment of the root system. The tree’s resources during these stages begin to be centrifugally concentrated and this coincides with initiation of growth from dormant and adventitious buds on the trunk and main branches.

As vascular dysfunction progresses the tree is increasingly hollowed by fungal agencies and when cambial dysfunction also occurs this may also result in the bark circumference becoming discontinuous. In the latter stages the survival of the tree will depend on the mechanincal stability of the trunk and main root system.

However, its effective longevity can be sustained by the viability of vascular columns on the trunk that directly link sections of the root system with fragmented upper parts of the crown or trunk. These cambial columns can form distinct but complete units as the parents tree starts to disintegrate. Being directly linked to their own root system the columns have the capacity to break free from the corporate system, rejuvenate and repeat some or all cycles from stages 1 to 10 (re-generating as phoenix trees).

Raimbault contends that this physiomorphological diagnosis can be applied to determine maintenance operations, independently from all actions that might typically be considered in response to pathological or mechanical conditions. He proposes remedial pruning that is informed by observation of the crown architecture in later stage trees (stages 6 to 10) to manage crowns that simulate trees in stages 1 to 4.

Further examples of this approach suggest sympathetic pruning work to enhance the form of young adults at stages 5 and 6 and refresh those at stage 7.Perhaps the most important aspect of this morphological diagnostic and management perspective is that the methodology leads to increased awareness and consideration of trees in the later stages of ageing (stage 8 and beyond) which leads on to crown contraction at stage 9 (sometimes termed retrenchment). It is here that the dynamic survival strategy of the tree is most evident.

Stage 10 can be interpreted as a turning point in a cyclic ageing process where the tree may be ‘reborn’ showing the potential for re-juvenation through ‘phoenix’ growth forms (as when, for example, a tree layers following collapse or when regenerating from internal adventitious rooting) so that the life cycle of the tree may begin again as a young establishing tree. In such cases the ‘young’ tree is paradoxically part of the original ancient stage tree, which also shows all the characteristics of the young establishing phase.

For further information a more comprehensive review of the tree ageing process and tree management implications from a morphological perspective can be found in the paper ‘Environmental Arboriculture, Tree Ecology and Veteran Tree Management’, by Neville Fay, Arboricultural Journal (2002) No. 26

• Further information on ancient and veteran trees: www.ancient-trees.org.uk and www.arborecology.co.uk

SEMINAR V – TREE MORPHOLOGY & DIAGNOSTICS

March 23-24, 2005: Venue Bristol .
Exploring the methodology, mainly developed and used on the Continent, that views the tree in terms of standard developmental morphological stages. This system is based on the assumption that the physiological and environmental history of the tree is somehow recorded in its form.

Variations from a norm may be interpreted in terms of perturbations in physiology and health. The system is used to understand the ageing process, physiological stress and as a diagnostic.

The seminar will specifically deal with applying a morphological approach to the principles of tree diagnostics and will cover:

• features of tree physiology in the context of developmental stages
• the basis for observing and recording tree architecture (stages of development of the aerial part and stages of development of the root system).

Through an understanding of the principles of morpho-physiological tree assessment it is intended that will broaden the basis for arboricultural diagnostic applications and increase the scope for appropriate tree management.

For further information and to book a place, please visit www.treeworks.co.uk/seminars or email seminars@treeworks.co.uk. If you do not have Internet access, please call Rachael on +44 (0)117 9105 200 to request a booking form.

Another commonly communicated concept is that a tree is suffering from a single disease or pathogen, the phrase ‘the tree is suffering from fungus x’ is a typical diagnosis.  On the contrary it is likely that fungus x is just the most prominent example and that there are many species present and functioning within a tree.  Attributing damage to a single causal agent is an oversimplification of what has actually happened to the tree.

The fact that a tree has succumbed to a pathogen is no bad thing though in Dr Rayner’s eyes.  Without decay there is no life since it is a process that releases nutrients and progresses the food chain.  Death, disease and decay are integral to the life processes associated with trees.  This misunderstanding is enhanced by viewing interactions between organisms in terms of territoriality and the occupation of space and the media that organisms offer one another is also an aspect of Alan Rayner’s concepts of inclusivity.

Olaf Ribeiro, Ribeiro Plant Lab Inc.  WA. USA described the processes necessary to support life within a tree.  He emphasized the positive role of microorganisms in the soil and root zones of trees.

These can be summarized as nearly all the physical, chemical and biological components, and it could be argued that without microorganisms soil is infertile dust.  This is of course one of those pieces of common sense alluded to at the start of this article but one that is all too often ignored or not properly understood.

This rhizosphere is an important part of the microbial-plant interaction and plants can attract microorganisms through chemical alterations of the rhizosphere.  This is of particular importance when considering the colonization of roots by mycorrhizae.  Dr Ribeiro then went on to discuss the role of mycorrhizae in protecting trees as part of an overall resistance strategy to potentially pathogenic organisms.  To adequately understand such processes there is a need to take account of territorial competition from plants and microorganisms and the conditions necessary for fertile and well-structured soil to sustain a healthy tree.  Again common sense but put across in an unequivocal way.

Stress of course is the common theme and this lead into the presentation of Dr Jan Cermak Professor of Tree Eco-physiology, Mendel University, Brno, Czech Republic.  Dr Cermak introduced a number of methods for the study of root patterns and water uptake in trees and presented some surprising data relating to the amounts of water coming from both surface and deeper roots.  We often think of water uptake in very simplistic ways, with the soil as a reservoir, the roots as a series of pipes and the stem as large pump.  This does not do justice to either the subtlety of the tree in accessing water or the complexity of interactions between the soil, the climate, the tree, and its competitors.

There was an immense amount of experimental information given and it is recommended that those interested in this area should take time to study Dr Cermak's numerous publications.

The data presented admirably demonstrated the detail that is needed to both measure and understand water flow to and within trees.  The data was derived from a multidisciplinary approach to whole tree investigation.  There was an immense amount of experimental information given and it is recommended that those interested in this area should take time to study Dr Cermak’s numerous publications.  However, particularly surprising was the way in which the rate of flow differed within different areas of the stem.  It was also put across that the transport of water in different parts of the stem related to the depth from which the water was extracted.

The slight disappointment, and I should emphasise the word sight, was that many of the experiments were carried out on evergreen coniferous species and I hope Dr Cermak has time to repeat some of his work with deciduous trees to determine whether such trees behave similarly or differently.

 

Marcus Bellett-Travers

PART II
Julian Forbes Laird
Like Marcus B-T, I too attended the Treeworks Environmental Practice seminar ‘Life Within & Beneath the Tree’ and, frankly, I was very disappointed.

I was disappointed that it took an arboricultural consultancy practice, rather than a professional body, to run what was quite the best technical seminar that I have ever attended.

I was disappointed at the lack of ‘official’ recognition for the seminar.

I was disappointed that there were no delegated present from any other major arb consultancy.

And I was disappointed that I was the only AA Reg Con present.

How can I make the reader understand?  This seminar was like attending a conference on zoology, only to find Nessie as keynote speaker.  (In this context, be of no doubt, Alan Rayner clearly hails from Loch Ness).

In my work, much of which is related to litigation, I am accustomed to absorbing and processing large amounts of detailed information in a short time.  But this is as nothing compared to the quantum of data with which the delegates were presented at this seminar.  And what data.

Alan Rayner has either lost the plot in quite spectacular fashion or has found a plot of which previously we were unaware.  Personally, I incline towards an amalgam of these two possibilities: the plot as we know it has been lost, but this is presented as an essential prerequisite to finding a deeper truth.  This concept is easier to accept from the Zen perspective, whereby the greatest capacity for enlightenment is found in the person with least knowledge.  But don’t necessarily take my word for it-I ‘ll buy into pretty much any off-the-wall idea (two triggers were pulled in Dealey Plaza, and I have a real problem with bi-directional lunar shadows…)

Jan Cermak simply buried the audience in an avalanche of information, outlining the findings of thirty years of research into trees’ systems that frankly beggars belief as to its scope and depth.  Studying Jan’s work is an activity, in and of itself, of several years’ occupation.  Whether this would be time well spent, I cannot really judge, as the sheer weigh of detail conspired to elude cursory appraisal.  I suspect, however, that much of it would be of more interest to our cousins in forestry.

Olaf Ribeiro. Remember this name: Olaf is set to be a giant in arboriculture.  Already a world authority on Phytophthora, he has developed proofs of two staggering phenomena relating to the means by which fungi of this genus select and infect their hosts: electrotaxis and chemotaxis.  Olaf has shown that tree roots emit micro-electrochemically, which emissions the zoospores of phytophthora detect and are attracted to.  A little extrapolation followed: give a tree an electric shock and you could deter phytophthora.  Alternatively, you might wilt the tree’s leaves, or make its lemons drop early (yes I know not all trees have lemons – I am paraphrasing).  The only prolme with Olaf, is that he is too busy discovering to publish his findings.  In any case, I suspect that finding peer referees for Olaf would be almost as difficult as finding them for Alan Rayner.  Anchoring all this was my friend David Lonsdale, who presented the audience with some charming anecdotes about medium altitude bog roll bombing of unsuspecting apple pickers, in the context of career spent systematically ignoring direct instructions from line managers whilst progressing unauthorized areas of professional study.  My conclusion: for a plant pathologist, David makes a pretty good arb…

So what did Fay & co offer the delegate: good data or the seeds of crypto-arboriculture?  Was this a seminar for David Attenborough or Fox Mulder?

This question may take certain arboriculturists a little time to resolve.  Those of more receptive mind, however, will be left in no doubt: the Treeworks Environmental Practice seminar was outstanding.  It provided this reported with greater intellectual challenge than any other single professional event which I have attended, and I came away with the germinating idea that all saprophytic decay fungi are latent I their hosts.  Taking this further: perhaps this explains the many instances where damaged trees do not develop parasitic fungal infections, and maybe in the future we will see more use of inoculation with pre-colonising saprophytes as a means of protecting trees against the nastier rotters.

Arboriculture is a new profession, and one based on an inherently unpredictable and dynamic locus: the tree.  It should, therefore, be of no surprise that there is much yet to discover, and that there are researchers working in relative professional isolation, of whom the vast majority have therefore never heard, who are breaking astonishing new ground.

And it is this which really disappoints: why was this immensely important seminar only a 40-delegate event? Where were the rest of you?

Julian Forbes Laird

PART III

A note from Neville Fay, seminar chairman, on some important issues that came out of the discussion session:

This seminar has been very well received with numerous requests for it to be repeated.  Other requests have been for the theme to be developed to further explore the soil-root-microorganism complexity.  There appears to be a real thirst for this level of information and quality for presentation to inform theoretical and practitioner knowledge of tree eco-physiology.

A very valuable aspect of seminar III was expressed in the question and answer session.

In this an interesting question was raised regarding the use of wood chip mulch; asking for guidance on appropriate treatments for trees where excessive doses of nitrogen have been applied in the past, usually in agricultural settings as a result of direct fertilization or indirect stock fertilization.  Related to this question was the risk of introducing pathogens (such as Phytophthora) into the soil through wood mulch application.

Olaf Riberiro expressed the view that the presence of lignin and cellulose mulch could enhance the presence of mycorrhizas which benefit indirectly from humic residues.  A wood chip medium can enrich the balance of decomposers and symbiotic fungal communities. 

Alan Rayner concurred with this view and offered some very interesting observations regarding the processes and effects resulting from the laying down of wood chip.  He described how basidiomycetes (the most commonly experienced fungal group which includes bracket fungi, mushrooms and puffballs) tend to appear late on in all kind of fungal ecological successional contexts.

Basidiomycetes by-and-large remove fungal competitors in the successional process because of the way they handle oxygen.  This is influenced by their cell boundary enzyme systems.  In this sense the chemical ecology of fungi can be understood largely by the chemistry associated with cell boundaries.  Enzymes such as peroxidase and phenoloxydase can cause the release into the surroundings of hydrogen peroxide, which in turn can knock out other organisms.  Alan Rayner considered that this was one reason why basidiomycetes replace other fungi late on in all kinds of succession.  This he thought would be especially the case in lignin-cellulose rich residues.  Basidiomycetes also have a mechanism known as hyphal interference, which links in with these successional processes.

In cases where high levels of nitrification have occurred, with potentially detrimental effects on trees, it was argued that as nitrogen pushes up early-phase organisms (such as Pythium and Phytophthora sp.), by adding lingo-cellulose rich residues it could be said that this is likely to encourage basidiomycetes succession with the effect of restoring the balance in the soil.

It was also argued that in such circumstances the use of non-composted or part-composted material would seem more beneficial than completely composted material, as this composting process of the wood chip would assist in reducing excess nitrogen from the soil ecology.

In answer to the question whether adding lingo-cellulose mulch to soil might adversely affect mycorrhizal communities, Alan Rayner’s view was that this would not be so, particularly in relation to the four main families of trees in temperate and boreal forests which form ectomycorrhizal relationships with basidiomycetes.  In the Northern hemisphere ectomycorrhizal relationships are associated with the pines, willows, birches, as well as with beech and oak.  As indicated above the application of residues would foster beneficial successional relationships in the micro-ecology of the soil rooting environment.  However, different consideration may be needed for species such as sycamore, elm and ash as they have endomycorrhizal relationships, which may even benefit more from nitrogen rich environments.

David Lonsdale pointed out that nitrogen- rich root environments also have the effect of including rapid root growth, which can increase susceptibility to infections from early successional species such as phytophthora.  It was also pointed out that as a tree ages there is a natural tendency, particularly in the post-mature stage, to increasingly produce saproxylic material, thus beneficially releasing lingo-cellulose content into the soil.

The presence of ‘coarse woody debris’ is a feature that might be expected to be found in abundance in old growth forests.  However, as in many urban and rural setting, it is common to remove such woody material, then it could be that such ecological processes are being inhibited with increased potential for the pathogenicity of early stage successional organisms. The view was also explored that applying log piles might be even more beneficial than wood chip, as this is more consistent with the gradual breakdown of material and potentially increases the range of beneficial fungal colonizers, consistent with natural forest processes.

Nev Fay