Life within & beneath the tree
Seminar III
Report on the third Treework Environmental Practice/AA Seminar held on 17th and 18th November 2005 at Keele University
Part I by Dr Marcus Bellett-Travers
Part II by Julian Forbes Laird
Part III by Neville Fay
PART I
Dr Marcus Bellett-Travers
‘Life Within and Beneath the Tree’, the third in Treework Environmental Practice’s series of seminars ‘Exploring Innovations in Arboriculture’ was a pleasure to attend. It focused on the physiological need of trees and fungi both as distinct individual organisms, whilst exploring the ways in which the two are inextricably linked. If there is one piece of constructive criticism, it is that the competition between fungi, trees, other plants and other members of the soil community for resources could have been explored further. However, the two days were so packed full of information and debate that there probably wasn’t room for this anyway. An excellent seminar has two things, one is participation from those who attend the other is that it gives enlightenment to those who participate. This seminar had both and the people at Treework should be commended, as should the Arboricultural Association for its support.
Neville Fay introduces the Seminar
Two points that stuck in my mind. Firstly, the complexity of the systems in which trees and fungi live and of which they are just a small part. Secondly, that much of what was said was scientific common sense and as individual pieces of information it could be said that they represented 'nothing new', but the trick was to bring the pieces of information together to give an holistic and rounded vision of the roles, needs, and interactions of some individuals of a complex system. There was however, plenty that was new and bold and innovative to arboriculture.
The concepts and ideas of Dr Alan Rayner, Reader in Biology, University of Bath, were focused on the idea of fungi as colonizers not as an army of wood-destroyers. Fungi are ever present in the environment as spores or organisms in soil or water. Their interaction with trees can be benign and advantageous to trees, either indirectly as part of soil organic matter decay and nutrient release or directly as symbiotic organisms such as mycorrhizae. Indeed, those fungi labelled as decay fungi or tree pathogens may coexist on or within trees without detriment to the tree. It is only when the tree coexistent relationship may change and the fungi become pathogenic.
This has lead Dr Rayner to examine the last word of Louis Pasteur 'Bernard was right; the microbe is nothing, it is the terrain that is everything'. What he was trying to get across was that the environment we and trees live in has the greatest effect on our outcome. 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.
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.
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 Treework 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 Treework 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