The 2016 International Elm Conference
Hosted by Lees Court Estate
In association with the Conservation Foundation
Conference Chairman: Dr David Herling
Elm Trees at Tonge, Sittingbourne, Kent
Thursday, 9th June 2016
Held at
Lees Court Estate
The Estate Yard Barn
Sheldwich Lees
Faversham
Kent, ME13 0NG
tel: + 44 (0) 1227 731331
www.leescourtestate.com
email: [email protected]
Conference Agenda
Thursday, June 09, 2016
9:30am
Registration & Coffee
10.00am to 10.15am
Welcome
The Countess Sondes (Host)
Dr. David Herling (Chairman)
10.15am to 10.45am
Dr. David Herling;
10.45am to 11.15am
Prof. Alberto Santini; "Lights and shadows of a possible strategy to cope with alien
and destructive forest pathogens: the example of breeding for DED resistance in
Italy"
11.15am to 11.45am
Prof. Juan Martin; The obtaining and use of elms resistant to Ophiostoma nova-ulmi
in Spain – past experiences and future prospects.
11.45am to 12noon
Break
12noon to 12.30pm
Dr. Max Coleman; Attack of the Clones.
12.30pm to 1.00pm
Dr. Alec Gunner; East Anglian Elms – An assessment of characteristics of surviving
trees
1.00pm to 1.30pm
Mr. Ronnie Nijboer; The Return of the Elm
1.30pm to 2.30pm
Lunch
2.30pm to 3.30pm
Tour of Disease Resistant Elm Trial Site on Lees Court Estate, including briefing on
Ash Dieback and its impact on the woodland.
3.30pm to 3.45pm
Break – Tea and Coffee
3.45pm to 4.00pm
Conservation Foundation
4.00pm
Summing Up and Final Question and Answers to the Panel
4.45pm
Conference Ends
Biographies
Dr. David Herling
www.ResistantElms.co.uk
David Herling is the creator of the website www.ResistantElms.co.uk, which is designed
as a portal for all who wish to find out about new disease-tolerant elm cultivars and
their suitability for planting. David’s chief interest is the English Elm, and narrowly
predates the great disease outbreak of the 1970s. In 2000, he set up, funded and
oversaw the Forest Research-approved Kentish Elm Conservation Programme, which
had as its objectives the identification, mapping, and practical conservation of surviving
mature elms in East and North Kent. His current research interest is the back-crossing
of hyper-resistant hybrid elms with those “native” survivors which show some disease
resistance as well as optimal landscape potential. His work has so far produced some 75
unique clones which await inoculation trials in two or three years’ time. In his day job,
David is Senior Lecturer in Contract and Public Law at City University London.
Title of Paper:
Prof. Alberto Santini
Italian National Research Council
Alberto Santini, forest pathologist PhD, is a Senior Researcher at the Institute of
Sustainable Plant Protection of the Italian National Research Council, based in
Florence, Italy.
His scientific interest is mainly focused on the management of invasive alien forest
pathogens. For 15 years he led the breeding for DED resistance team in Italy. He
published more than 20 full papers on this issue and patented and released to the
market three DED resistant elms clones.
Title of Paper: "Lights and shadows of a possible strategy to cope with alien and
destructive forest pathogens: the example of breeding for DED resistance in Italy"
Prof. Juan A. Martin
Technical University of Madrid, Spain
Juan A. Martin is Associate Professor at the Technical University of Madrid. He earned
his PhD in Forestry Engineering from the same University in 2006. He has about 6
years of experience in teaching and 14 years in research, focusing on Forest Health.
Primary interests are host defence mechanisms of woody plants against fungi, ecological
wood anatomy, tree breeding against pathogen, and diversity, functions and
biotechnological applications of endophytic fungi. One of his main research lines has
been the study of elm resistance against Dutch elm disease pathogen. He has been
principle investigator of three competitive research projects, has over 32 referred
publications, and currently co-ordinates the Forest Health Group of the Spanish Society
of Forest Sciences.
Title of Paper: The obtaining and use of elms resistant to Ophiostoma nova-ulmi in
Spain – past experiences and future prospects.
Dr. Max Coleman
Royal Botanic Garden Edinburgh, Scotland
Max Coleman works at the Royal Botanic Garden Edinburgh in the field of science
communication and public engagement. His elm studies grew out of noticing that some
elms appeared able to survive Dutch elm disease in the English Midlands. Molecular
taxonomy of elms carried out at the Royal Botanic Garden Edinburgh highlighted the
significance of ancient clones in understanding patterns of elm diversity. Most recently
Max has explored elm diversity on the Isle of Man. Here the presence of a widespread
clone has again confounded botanist and the application of DNA fingerprinting has been
necessary to confirm identifications. Max is the Botanical Society of Britain and Ireland
referee for elms and gets a steady trickle of identification queries from vice county
recorders and society members.
Title of Paper: Attack of the Clones.
Dr. Alec Gunner
Alec Gunner is currently locating and characterising surviving strains of U.minor and
its hybrids which show potential resistance to DED. Alec’s interest in elms dates back
to the mid-1970s when as a small boy he remembers the impact of the major outbreak of
DED in Kent, where he then lived. This interest was re-kindled through finding a
number of mature, surviving trees in South Cambridgeshire, South Suffolk and North
Essex where he now lives. Trees with suitable characteristics are currently being
propagated for an inoculation trial, to assess their suitability for propagation. In his day
job, Alec is Section Manager – Specialist Materials & Joining at TWI Ltd, a leading
provider of contract research and development on behalf of industry.
Title of Paper: East Anglian Elms – An assessment of characteristics of surviving trees
Mr. Ronnie Nijboer
Noordplant, Holland
Ronnie Nijboer is the co-owner of the tree growing nursery, Noordplant in the North of
Holland. In 2000, Ronnie became interested in the tree species Ulmus in relation to
Dutch Elm Disease (DED). The cancellation of the DED sanitation in 1992, meant that
by the late 1990’s, there was a strong outbreak of elm disease. Dutch tree officials lost
confidence in elms and this led Ronnie to conduct a thorough study of the disease. The
study found that there was a fear of planting new elms which were largely based on
emotions rather than rational knowledge. A small group of elm lovers managed to
refute the objections step by step. It has taken over 10 years, but in Holland the elm is
back where it belongs: in the top 10 ranging of the most planted tree species. It’s time to
convince the rest of the world, to start at the UK!
Title of Paper: The Return of the Elm
Lees Court Estate, The Countess Sondes
The Lees Court Estate has been described as the finest Estate in Kent. The Estate has
been in the Sondes family for the past 700 years and became the centre of The Countess
Sondes’ life on the death of her husband, Henry George Herbert, The Fifth Earl Sondes
in 1996.
The Estate, during the early 1900’s, was 85,000 acres. Today the Estate is 6,900 acres
with a core of 2,663 acres around the villages of Sheldwich and Badlesmere with the
balance at The Swale Estuary, Oare and Faversham Creeks.
The Estate is known for its innovative work in agriculture, Non-Food Crops and its
renowned shoot.
In 2011, the Estate, with assistance from the Forestry Commission, applied for the
English Woodland Grant Scheme (eWGS) to assist funding woodland operations. The
enhanced grant aid is applicable to woodland located in the North Downs Area of
Outstanding Natural Beauty. The Scheme has been approved, and work commenced in
2012, and will run until 2017.
The Scheme is to undertake areas of coppicing, felling and thinning whilst leaving
maiden and other native broad-leaved trees. This work will provide a patchwork of
different aged trees throughout the woodland and will provide improved habitat
diversity for flora and fauna. Long-term coppicing will also create a varied and improved
shoot because of the range of growth stages and the warmer ground conditions for birds.
Much of the conifer woodland will be removed in selected areas, which will allow the
natural regeneration back to the native broad-leaved trees and improving wildlife
habitat.
The Estate also hosts the United Kingdom’s first formal elm adaptation trial.
The Estate’s woodland is managed by Stephen McCarthy, Woodland Management &
Consultancy.
The Conservation Foundation
In 1982 The Conservation Foundation was formed by David Shreeve and David Bellamy
to promote positive environmental news, awareness and action.
An environmental entrepreneur from the outset, for 30 years we have been creating
original initiatives that have inspired and enabled thousands of people to engage with
the environment.
Our projects are run as partnerships - with corporate and individual sponsors,
government departments, media organisation, trusts and foundations. We also create
and manage award schemes, awareness campaigns, publications and events covering a
wide range of environmental issues.
Currently there are two projects relating to the Elm.
The Great British Elm Experience in which The Conservation Foundation is attempting
to unlock the mystery of why some trees survived Dutch elm disease which wiped out
over 25 million elms in the UK.
The second is Ulmus Maritime which is a project supported by the Heritage Lottery
Fund to help protect the elms, regenerate the population and raise awareness of this
exceptional feature of the Sussex landscape
The Lees Court Elm Adaptation Trial
493
493
SZ
SZ* P
P
493
493
506
506
M
M
M
M
P
P
M
M
P
P
SZ
SZ*
462
462
462
462
506 506
493
493
506
506
SZ*
SZ
Adz
Adz Adz Ret
Ret
DdA DdA DdA Adz
Adz
Adz
Ret
Ret
Holly Grove end
Ret
Ret
DdA DdA DdA
Stringman’s end
SZ = San Zanobi
M = Morfeo
FL 506
FL 493
FL 462
P = Patriot
Adz = U. minor “Ademuz”
DdA = U. minor “Dehesa de Amaniel”
Ret = U. minor “Retiro”
Asterisks = plants which have failed to establish (San Zanobi x 3)
The Lees Court Elm Adaptation Trial
An adaptation trial is one in which several replicates of clones are planted on a grid
(typically 5 x 5 metres), more or less randomised, so that their growth, form and general
state of health can be monitored. Once they are established, height and girth
increments will be taken and compared over a period of a few years.
This planting of 9 clones at Lees Court is believed to be the first formal resistant elm
adaptation trial (as opposed to informal planting) undertaken in this country. It was
inspired by the main Italian adaptation trial at Castellaccio, Umbria, and by Andrew
Brookes’ work at Great Fontley Farm, Hampshire. The first plantings took place in
2015 and were added to in 2016. The clones involved derive chiefly from the Italian and
Spanish elm breeding programmes, and are those which I subjectively consider to
combine excellent disease resistance with English landscape potential. The US clone
“Patriot” I also included, along with one other Italian clone which probably has only
medium resistance but notable form and vigour (FL 462).
Cont’d
A brief description of the 9 clones follows:
San Zanobi is a crossing of the old Dutch cultivar “Plantijn” and Siberian Elm. It is a
relatively fastigiate tree, which shows excellent vigour once established. When
inoculated with DED it has sustained wilting of 19.5%, and dieback of 8.5%. It is
therefore unlikely to be much affected by DED under field conditions. However, the
Lees Court planting has already yielded one valuable result. Half of the 6 SZ originally
planted failed to establish. These were the only losses in the trial. They will be replaced
when new stock is available.
Morfeo arose from the crossing of a Dutch elm (x hollandica) and French field elm, with
Ulmus Chenmou from eastern China. It is distinguished by very sturdy growth, but a
slight greyish or glaucous leaf colour. Its resistance to DED is optimal. However, it has
had the misfortune to have been the subject of a scare involving the very serious
condition “Elm Yellows”, and may not have ideal levels of resistance to this disease. The
stock provided to Lees Court has been certified free of Elm Yellows, and has been
inspected by the relevant government agency.
FL 506, sometimes known as “the brother of Morfeo”, shares that clone’s ancestry. It is
slightly slower-growing than Morfeo under most conditions, slightly less DED-resistant,
but has little of the greyish or glaucous leaf colour of its stablemate. Its leaf shape quite
strongly expresses the Wych Elm genes present in its Dutch elm ancestry. My own view
is that sustained back-crossing of 506 and Wych Elm could produce a tree well suited to
woodland planting in this country. Both Morfeo and FL 506 display spectacular autumn
colouring under some conditions, which could be regarded as an advantage or not,
depending on your point of view. English and Wych Elm did not.
FL 493 is a highly complex clone, three quarters European-derived with one eighth each
of Himalayan and Siberian Elm. In Italy, it has proved very fast-growing and robust.
Its DED resistance is among the highest produced by the Italian breeding programme,
and amounts to apparent immunity. I have used it as the female parent in my own
programme of back-crossing with English field elms. Opinions as to its form vary, but I
feel little doubt that it is a usable tree for general landscape purposes. The new growth
is vulnerable to blackfly infestation.
FL 462 is a vigorous, monopodial elm which has a drooping leading shoot. Its ancestry
is not fully documented, but appears to include one hybrid which was not very DED
resistant at all. It has peeling bark, which suggests U. parvifolia genes. Its foliage is
bright rather than dark green. It is included in this trial as an outsider, for much the
same reason as the Italians seem to have kept it on: it is very striking, and deserves a
chance.
Patriot is another very complex hybrid, created by Townsend in the United States, but
in no way related to American Elm. US testing suggests that its DED resistance is very
good indeed, but corroboration of this from European testing is currently awaited.
Patriot seems to vary considerably in form according to the soil and climate in which it
is grown, but it is at least potentially monopodial. Its major problem is that its height
increment tends to outstrip girth, so that it may be wrecked in a windy climate. I once
received a one year old Patriot which, in its second year grew 250cm. The tree has never
recovered.
Cont’d
Ademuz is a Spanish selection from near Valencia of pure U. minor (European Field
Elm). Its disease resistance is somewhat better than that of the wholly reliable hybrid
U. x “Sapporo Autumn Gold”. Its form is good but by no means perfect, with a tendency
for the leading shoot to be overtaken by strong growth from below. The leaf is
unremarkable, but this is quite as “native” a tree as any field elm currently growing in
this country, and it seems highly unlikely to be affected by DED.
Dehesa de Amaniel is another U. minor selection in this instance from Madrid. Its
resistance, when inoculated with DED in the lower third of the trunk, is extreme.
Vigour seems very good, and leaf shape quite close to that of some “native” elms. The
few available photos of an older tree suggest a leaning habit, but may reflect the clone’s
response to growing conditions in the harsh climate of Madrid. The whole point of an
adaptation trial is to see how such a clone performs here. At the very least it is
potential breeding material, given its extraordinary disease resistance.
Retiro is the third of the Spanish U. minor accessions on site. The plants were the
smallest of all those included in the trial. They appear to branch very young, and from
very low down the stem. Retiro has nevertheless made excellent growth as planted by
Andrew Brookes in Hampshire. Its DED resistance appears to be on a par with that of
U. x Sapporo Autumn Gold.
There remain 6 spaces to fill in the Lees Court Elm Adaptation Trial. These may be
taken next year by “Fuente Umbria”, another Spanish clone due to be available to us
shortly. Fuente was first billed as U. minor, but genetic sampling now reveals it to have
some Siberian Elm ancestry (by no means unusual among Mediterranean field elms).
That disqualifies its further use in the Spanish programme, but does not diminish my
own interest in it. Its DED resistance is broadly comparable to U. x “Sapporo Autumn
Gold”.
Lees Court Elm Timber Trials
In Holly Grove, in addition to replanting of native broadleaves, we have two longer-term
trials of elms whose interest lies in their timber qualities. They are the Italian hybrid
“Fiorente”, and the Dutch/French hybrid “Vada”. There are 40 plants of each, and they
seem to have established well on a rather poor soil.
Fiorente is a crossing of European Field Elm with Siberian Elm. It is a fairly fastgrowing tree distinguished by straightness of trunk and upswept branching. Its DED
resistance is only moderate, but it is capable of “walling in” instances of infection which
therefore seem to result only in a few dead twigs. Italian studies have demonstrated
that the timber qualities of the modern hybrids are similar to those of U. minor.
Fiorente’s straight growth therefore shows promise of useful lengths of straight elm
timber. The issue, for me, is the junctions of major branches with the central trunk,
which tend to become very pronounced over time – almost tumescent. Brashing of some
lower branches may be necessary.
Vada is a Dutch/French clone of high DED resistance. It is moderately fastigiate, but
late-leafing and of no great aesthetic quality. It was amongst several clones received
from Ronnie Nijboer some years ago, and the quality of its wood immediately
distinguished it from the others. It is extraordinarily tough. If this characteristic is
maintained in the mature trunk, then we have here an elm of a most unusual kind.
Conscious that some traditional crafts such as niche boat-building still have need of
straight elm timber, I was keen to see what these two clones could do under English
conditions. I am extremely grateful to the Lees Court Estate, and to Steve McCarthy in
particular, for providing us with the opportunity in due course to find out.
www.ResistantElms.co.uk inoculation trial
At a site in the Middle Medway Valley, unconnected to the Lees Court Estate, I have
established a trial plantation of elms received from associates plus those of my own
breeding, ready for future inoculation testing. The intention is, of course, to begin to
assess their true DED resistance. Planting began in the spring of 2016.
To be ready for inoculation, the trees need to be about 2 metres in height. That gives
you the time scale for results.
There is currently a total of about 170 elms on the site, which is fenced, gated, on heavy
but fertile loam, and south-facing. All plants are protected by tall tree guards against
rabbits. Deer are not thought to be present – they completely destroyed a substantial
planting of Italian clones in the Weald of Kent.
The clones involved are these:
Row 1:
Ademuz, Dehesa de Amaniel, Retiro, Morfeo x Sapporo Autumn Gold (x
2), Columella op (x 4), Morfeo x U. minor “Tonge Mill”.
Row 2:
FL493 x Patriot (x 30), Vada (x 3), U. pumila “aurescens”, U. “Accolade”.
Row 3: FL493 x Patriot (x 20).
Row 4: FL493 x U. minor “Tonge Mill” (x 27)
Row 5: FL493 x U. minor “Tonge Mill” (x 27)
Row 6: FL493 x U. minor “Tonge Mill” (x 24)
Plus, one specimen of the pendulous Actons Farm elm from the borders of Hertfordshire
and Essex, doubtfully classifiable as U. minor or U. x hollandica, but a superb survivor
for all that. It may well be a “nurseryman’s elm”, growing so close to the famous Rivers
Nursery at Sawbridgeworth which had an interest in elm, and perhaps arising from
open pollination of U. x hollandica “vegeta” (Huntingdon Elm). I have supplied this tree
to Brighton, and can offer it to anyone else interested. Original elms of a pendulous
habit were always associated with the Herts/Essex hybridisation zone.
In the list above, you will see the predominance of my hybrid “FL493 x U. minor “Tonge
Mill””. The “Tonge Mill” strain of U. minor, growing near Sittingbourne in Kent, is a tree
which in the mature form (although now finally failing) has resisted DED for 40 years.
It is what Max Coleman would describe as a “pseudoplotii”, which is to say an elm which
exhibits some characteristics of Plot Elm without in fact being that taxon in genetic
terms.
The distinguishing features are its heavily swagging and therefore rather Victorian
ranks of foliage, combined with its narrow crown. Only much time will tell whether I
have succeeded in combining its archaic looks with the resilience of FL493 in any of my
hybrids.
In order to stimulate debate at this year’s conference, here is a
selection of questions which seem strongly relevant to the state of
elm development today. I very much hope that our expert guests
(Alberto Santini, Juan Martin, Ronnie Nijboer, Max Coleman and
Alec Gunner) will be touching on at least some of them.
(a) Institutional questions
Where do you see your development work now heading?
Juan: what are the likely timescales for the Spanish programme as regards the
patenting and international marketing of your U. minor clones, and your ongoing
development of new elite U. minor selections?
Are you looking for international
partners? Would you wish this country to be an eventual market for your U. minor
clones? In the meatime, how we can best help?
Alberto: has the Italian programme effectively come to an end, or may we look for any
future developments?
Ronnie: is your own involvement in elm breeding, as opposed to nursery tree
production, effectively a private hobby (as mine is for me)? Do you expect to be
introducing any new elm clones?
Max: has your work and that of others with U. glabra taken us any closer to the
identification of clones with a degree of field resistance? Have any inoculation trials
taken place? If not, are they planned? Do you have an ongoing interest in genetic
study of elm populations, and institutional back-up for that?
Alec: you’ve been observing some of your E. Anglian clones for a few years now, and I
know you will be proceeding to an inoculation trial. Are some of your genotypes
remaining within the parameters we tentatively set in 2013 in addition to
distinctiveness from surrounding elm populations – mature trees remaining, and virtual
absence of disease even in younger growth?
All: it now seems that the Oxford
Harcourt Arboretum are prepared to
modern disease tolerant elm clones.
connection? What are the synergies?
Botanic Garden and the University of Oxford’s
take an active interest in becoming involved with
Do you see opportunities for yourselves in this
What should we be jointly trying to achieve?
All: If the University of Oxford does decide to become involved, will you be able to
supply some of the products of your breeding/selection programmes for planting? If so,
to what extent do you want to be involved in dialogue about which are chosen for
inclusion? And for those of you not in this country, are you able to engage fully with
phytosanitary processes and certification?
Cont’d
(b) Testing tolerance – some detailed queries about disease, science
and best practice
Alberto, Juan, Ronnie: In inoculation trials, it seems that the Italian programme
opted for inoculation in the upper third of the plant while the Spanish programme
inoculated in the lower third. Presumably the second of these methods is the more
severe. Is it possible to recommend/agree a single protocol, so that future results are
more genuinely comparable? With a very severe inoculation technique, is there a
danger of screening out clones which would in fact display satisfactory disease tolerance
in the field?
Juan: Most European inoculation testing appears to report data for wilting and for later
die-back. The Spanish results seem not to be so specific. Is it possible to elucidate this?
It seems relevant, given that Eric Colin reports that inoculation of the clone “Dehesa de
la Villa” initially produced little wilting, while the plant was later killed outright. Some
local U. minor at first suffered considerable wilting, but survived.
Ronnie: In the Inoculation trials reported in Forest Science 51(2) 2005, differing
degrees of severity are reported for different trials ranging from “high” (eg.
Geraardsbergen 2001) to “low” (eg. Madrid 2001). By what means can a standard level
of severity be achieved?
The same paper reports the use of a variety of strains of Ophiostoma inoculum across
these trials, often locally-derived. Is this capable of leading to disparate and noncomparable results, and if so, are any strains of reliable or standard inoculum available
and recognised as being the ones “of choice”?
Alberto, Juan: What are your comments on the US method of in vitro inoculation of
young trees followed by observation of “volume of discoloration”? Is this method of any
value in establishing the disease tolerance of elm plants?
Alberto, Juan, Ronnie: Can an elm be regarded as Ophiostoma-tolerant if the
majority of inoculated plants show good resilience whilst one or more are severely
damaged or killed? Is “tolerance” to be regarded as a matter of averages, or should it be
absolute – no losses? I ask in connection with FL316, seen dead at Antella subsequent
to inoculation, but included amongst the 24 “resistant” clones on whose performance the
2010 “Genotype x Environment Interaction” paper was based.
All: in this country, we took a severe blow when evidence of Elm Yellows was detected in
a parcel of U. x Morfeo grafted onto U. glabra. How has your thinking about the threat
of Elm Yellows developed since then? Have you experience of testing for susceptibility
to Elm Yellows? Should UK developers such as Alec and me be learning how to do so, or
can we hope that what we breed or find will have average field resistance? Eric Collin is
of the view that Elm Yellows have reached the latitude of Paris, and may now be further
north than that.
All: what is your opinion of some growers’ practice of raising stock for sale by grafting
(eg. onto an U. glabra rootstock)?
Cont’d
Juan: I believe you have said that Elm Yellows is not currently a threat in Spain. Are
you confident that your U. minor clones show reasonable resistance? What is your
opinion of the Italian method of soaking cuttings in warm water (proven to eliminate
Elm Yellows) before they are rooted?
All: Given the widespread occurrence of Ulmus glabra in European montane woodland,
its status in this country as our only indisputably native elm, and its apparently strong
resistance to or tolerance of Elm Yellows, do you have any plans to select for
Ophiostoma resistance in this species?
(c) Questions particular to U. minor var. vulgaris – the English
Elm – and attempts to use it for back-crossing
Juan: Has your work in the Olmedo de Rivas-Vaciamadrid led you to conclude that any
of the Italian-derived U. minor var. vulgaris there may have greater than expected
tolerance of Ophiostoma? Or is the relatively slow progress of the disease on that site
better attributed to the use of chemical compounds sprayed at the base of these trees in
connection with animal husbandry on this site (mentioned in a published paper)?
Max: have you observed any unexpected slowing of disease development on the Isle of
Man, or is it your conclusion that the superior performance of elms there is the result of
sub-optimal climatic conditions for the Ophiostoma vector, Scolytus?
Alberto, Juan Ronnie: In your experience as elm breeders, have you found any
correlation between complexity of hybrids and low fertility? I have not. My most
successful cross ever was the highly complex FL462 x Patriot. Meanwhile, attempted
crosses between supposedly much “simpler” genotypes have wholly failed.
All: my most complex hybrids (eg. FL493 x Patriot), have a tendency to lack strong
character and to appear as “generic hybrid elm”. Does the science support an
expectation that the crossing of already complex hybrids may lead to a “melting pot”
result?
Ronnie, Max: In my attempts to use var. vulgaris as a pollen donor, and under optimal
conditions, I have failed almost totally. I did get as far as achieving some originally
fertile embryos which aborted at a late stage. Have you noted a tendency of var.
vulgaris pollen to be infertile, or to cause late abortion of previously fertile embryos? Do
you find var. vulgaris hybrids in the field?
Max, Juan: It is now commonly thought that var. vulgaris is a single clone (“Atinian
Elm”). Have you nevertheless observed genetic variation within this taxon? Of two
trees growing side by side in Preston Park, Brighton, one is heavily galled by the
campestricola mite while the other is wholly free of it. Does this suggest genetic
variation? Does var. vulgaris persist in the field not only because it is female sterile, but
also because it is an inept pollinator?
Alberto, Juan, Ronnie: My protocol for hybridisation attempts is to apply pollen less
than one day old to flowers, two or three times a day, from the moment they begin to
open until anther dehiscence (typically 6-10 days in total). The female parent is then
kept indoors, frost-free, and at temperatures as close to the low-mid 20s as possible. Is
this a correct approach? Can one “over-apply” pollen?
Cont’d
Ronnie: you successfully crossed var. vulgaris with Nanguen and with Plantijn, I think.
Did you try other any other crosses which completely failed to work? I am convinced
that I will never succeed in producing a single embryo from Morfeo x vulgaris. How did
you choose the female parents with which you matched vulgaris as pollen donor? What
are you now doing with your semi-resistant progeny of your hybridisations?
David Herling
www.ResistantElms.co.uk
Rochester Kent, June 2016
The growth and ultimate form of English Elm
Perhaps the most frequently asked of all questions about the modern elm cultivars is:
will they look like English Elm?
The aim of this note is to provide some insights into why English Elm looked as it did –
typically a figure of eight shape – and to warn that characteristics currently sought by
the tree nursery trade may actually be those least likely to produce any approach to a
look-alike.
But first, back to the question. Will the new elms look like English Elm? The
straightforward answer is that they almost certainly will not. However, this is a
moment at which the glass may be perceived to be either half empty or half full. On the
one hand, not even Ulmus minor, the field elm, (of which English Elm is merely a
variety) tends to look identical to English Elm. On the other hand, even an elm as
obviously unlike English Elm as Sapporo Autumn Gold can add an elm-like note to a
landscape more effectively than any other species. English Elm understood as an object
is unlikely ever to be precisely copied through the breeding of new clones. English Elm,
if understood as the landscape presence of cohesive crowns of terminal twigs roofing
distance without blocking it, can certainly be approximated.
What follows would ideally be illustrated by 150 annual photographs of a given tree
from its first year onward. Time being short, words will largely have to do.
The new elms which appeal to the nursery industry are monopodial (they have a strong
central trunk and light branching from the outset) and have relatively narrow crowns.
These are trees whose growth is predictable, proportioned to the restricted space of
urban sites, unlikely to cause costly problems, and easy to handle in the nursery. There
is little economic incentive for industry investment in trees which do not meet those
criteria, regardless of their putative value to the open landscape. English Elm, even if it
stood a chance of survival nowadays, would certainly be passed over.
The crucial characteristic of English Elm is that in its very early years it is not obviously
a monopodial tree. At the end of its first year, it will be a more or less upright shoot,
probably slightly recurved at its tip. However in the following year, it is likely that the
terminal buds will develop into co-dominant leaders. At this stage it seems improbable
that a single straight trunk will be formed.
Nevertheless, by the end of the tree’s second year, the influence which will enable it
despite present appearances to form a towering vertical trunk may already be very
subtly apparent – one of the leading shoots is likely to be further from the vertical than
the other, and may have made slightly less growth. The other is prevailing; the
phenomenon of apical dominance is beginning to make its mark.
In the third year, both branches are likely to produce two or three strongly growing
shoots. At least one of those from the year 2 branch which was the more leaning may
now be at a very lax angle, and its weight will force that parent branch further from the
vertical. The tree’s form would now seem ruined; but from the more vertical year 2
branch one of the new shoots will probably be close to vertical. It will exert apical
dominance over all other growth, and the shoot which bore it will now gain in girth over
its rival.
The form of the sapling is opening up. The same process is repeated for perhaps 20 to
30 years. Almost always, one shoot will correct or over-correct the deviation from
vertical in the preceding year’s shoot from which it arises. This will be the shoot which
tends to make the most vigorous growth. A trunk of sorts is beginning to form. It will
not be a straight vertical, but a series of near approaches to the vertical quite possibly
with one or two abrupt kinks. As the trunk gains more girth, the lowest kinks will begin
to disappear.
The ultimately monopodial character of English Elm is thus the product of successive
indirections and subsequent corrections.
Meanwhile, the would-be leaders which lost the competition have been forced into
growing outwards from the trunk, and although they remain vigorous branches they are
beginning to make less growth than before. It may be horizontal growth or below
horizontal, because the bulk of the young tree above is beginning to cast a depressive
shade. Shoots from what are now side-branches will dart out in whatever direction
light is to be had, but because of their angle they will have reduced vigour. Were they
over-vigorous, as in Dutch Elm, that habit would drastically affect the shape of the
mature tree, leading to a broadly spherical shape and an open, ragged crown.
The very oldest and lowest side shoots are now shaded out completely, and will either
die or at least cease extension growth. The young tree is now a bulky and amorphous
pyramid, ragged at the bottom and broad a little higher up, where the side branches
have had longest to reach out. One would look in vain at this stage for any hint of what
the structure is to become. That should be borne in mind when assessing modern elm
cultivars. The best of them are likely to go through a similarly amorphous phase.
Depending on soil, hydration, climate, exposure , latitude, and the proximity of other
trees of similar height (and leaving out of account extreme situations), this phase may
see the tree reach 30 to 60 feet in height. That assembly of variables determines the
energy which the tree has for extension growth before it switches to maximising its
photosynthetic potential with a view to the production of seed.
Extension growth and seed production are in complex balance. The setting of seed, even
if it is in fact infertile, is debilitating and reduces the plant’s vigour; in fact in some
years seed-set has apparently been so heavy that observers reported the near-death of
elms from the effort involved. Seeding is nevertheless needed for reproduction (the fact
that English Elm has actually evolved to be self-sterile is irrelevant). Meanwhile, early
extension growth is essential in order to produce the largest viable structure for the
later production of seed, and the requisite exposure to light.
At the stage in the tree’s development when seeding begins in earnest (notably late in
the case of English Elm and sparse in comparison to some other elms), its capacity for
vigorous extension growth lessens, and apical dominance diminishes. The result seems
to be that amongst the fan of new shoots at the tree’s apex the tendency for the most
vertical to predominate over the others is far less than it was in the younger plant.
Branches developing at a considerable angle to the vertical are able to take almost as
much of the tree’s energy as do those which are more erect. In consequence a dome-like
crown begins to form. In it, a continuation of the main trunk may be found, or it may
not, depending on the tree’s vigour. Persistence of a central trunk high into the canopy
was frequent in the ideal growing conditions of the Vale of Gloucester, parts of
Berkshire, and Middlesex. In the somewhat less favourable environment of Wiltshire or
Devon (for example), a crown lacking a central axis was the rule.
Whichever is the case, the tree has reached its junction. Below is the central trunk
surrounded by initially strong side branches depressed later in their development by the
assertion of dominance at the tree’s apex, and by its shade. Above, the crown begins to
develop, now that apical dominance is waning.
The advantage of a crown is that it achieves an array of twigs with maximum exposure
to light for the production of seed. The branching which begins to constitute it is soon
carried on not by post- juvenile extension growth, but by mature shoots which have
seeding as their primary function. They will grow in any direction in which they find
access to light, be it horizontally or even downwards if that gains them any advantage of
exposure. This continual competition for light now leads the twigs which will form
the scaffolding of the crown to grow in haphazard directions, so that as they mature, the
branches are crooked. Terminal twigs will develop efficiently to fill any space in the
array. Apical dominance now gone for good, their growth will be slow and uniform, so
that the characteristic bounding line of the elm’s canopy begins to form.
The establishment of the canopy has a profound effect on two sectors of the tree’s lower
foliage. Immediately below the junction, the lateral growth from the main trunk is now
substantially shaded and much slowed. This is why the lower bowl of the figure of eight
narrows towards its top. However, lateral branches lower down the trunk are less
shaded, able to continue their extension, and the lower half of the tree’s silhouette now
notably bulges at its midpoint. The most vigorous side branches may extend sufficiently
far from the trunk to escape much of the crown’s shade. In fact the angles adopted by
these “successful” side branches can often be seen to correspond closely to phases of the
crown’s development. Relatively vertical growth is initially made by the juvenile
branch, before the crown’s development reduces light from above. A phase of horizontal
extension follows, corresponding to the continued availability of lateral light. Once the
branch has extended sufficiently to escape the shade of the crown, it will turn upwards
again.
At the junction and immediately above it, at the base of the crown, the shade of the
canopy above is extreme. Here, most growth will die. This is why the base of the
branches arising from the junction tends to be visible while the tree’s scaffolding above
and below is completely concealed by foliage.
The shape of the tree now approximates to two crowns more or less distinctly divided – a
lower and an upper, though the most successful side branches may mediate between the
two (forming what is often called the “pie-crust” outline of English Elm). This hierarchy
of crowns is articulated by the junction zone which is relatively free of foliage. As a
result, it is possible in a sense to see through an English Elm at its midpoint. In
addition, the openness at the base of the upper crown may make it appear less like a
globe of foliage and more like a parasol or roof, though that tendency was much
influenced by local conditions. It was often seen in an extreme form in Cornish Elm, due
in part to the effects of wind and salt.
If this account is correct, English Elm owed its form (a) to a tendency for the current
year’s growth to fan outwards in the form of co-dominant leaders of which one would
later prevail through apical dominance; (b) to the ability of its lateral branches to grow
at a wide range of angles to the vertical in search of light, to which the tree was highly
sensitive; and (c) to the comparatively late onset of seeding (sexual maturity) which
favoured the formation of a tall central trunk before seeding caused it to give way to
crown development.
This apparent hyper-sensitivity to the relative intensity of light is not surprising in a
tree growing far north of its natural range, now generally thought to be central Italy.
The uniquely “English” silhouette of fully developed English Elm actually arose in part
from the tree’s limited adaptation to this latitude.
The nursery trade, however, tends to select clones of a relatively fastigiate or pyramidal
habit providing guaranteed upright growth from the outset. This results in weak side
branches which curve upwards as far as space allows to mimic the vertical growth of the
leader. Examples from across the range of breeding programmes are Columella,
Cathedral, the very vigorous San Zanobi seedling FL634, and to an extent Lobel and
Vada. The consequence is a tree in which there is actually insufficient distinction of
character between trunk and lateral growth; the latter is merely a weaker (perhaps
much weaker) and off-centre version of the former. Clones of this type are not likely to
display a hierarchy of form at maturity, nor the coherent crown so often seen in English
Elm. Clones of apparently more unruly early growth, such as FL 493 or Morfeo, have a
better chance of developing into trees which will recall the place of English Elm in the
open landscape.
David Herling
www.ResistantElms.co.uk
Rochester, Kent, December 2014
Elm Cultivar Selection
A small selection of “traditional elms” and modern hybrids will be on display
outside the conference venue at lunchtime for the purposes of comparison and
illustration of some of the points to be made during the first part of the event.
1. Ulmus procera, aka U. minor var. vulgaris “the English Elm”
The benchmark elm of the south and midlands of England, unfortunately very attractive to
Scolytus feeding and possessed of very little inherent disease tolerance. The campestricola
galling of the leaves is not unique to English Elm, but is found on fairly few other field elms
in the U. minor group. Disease inoculation generally leads to about 85% wilting, about 75%
dieback, and thence to the speedy death of the tree.
2. Ulmus laevis, the European White Elm
Generally thought not to be native to this country, and rarely encountered here, laevis is
characteristic of damp woods by the main rivers of central and Eastern Europe. It tolerates a
variety of soils, but performs particularly well in waterlogged conditions. It possesses very
little resistance to Elm Disease, but is generally not touched by Scolytus and escapes
infection for that reason. When well-grown, it can be a very imposing and rustic tree.
3. FL 509 (“Morfeo”): hollandica x chenmoui (Florence)
Bred in Florence, Morfeo has demonstrated very high disease tolerance. Its form is variable
across different environments, appearing to good advantage in central Italy but disappointing
in Lincolnshire. In the south of England its stability to wind-rock initially distinguished it as
a promising cultivar. However, the detection of Elm Yellows in some stock produced by
grafting onto U. glabra has shaken confidence in it, whether rightly or wrongly. In this
country, Morfeo tends to have densely pubescent leaves and therefore a slightly grey tone to
the foliage.
4. FL506: hollandica x chenmoui (Florence)
This is a sibling of Morfeo (see above), distinguished from it by slightly lower but still
excellent disease tolerance, a slightly slower rate of growth and perhaps less stability. On the
plus side its leaves tend to be a fresher green, and have something of Wych Elm in their size
and character.
Cont’d
5. FL493: complex hybrid which is 6/8ths European elm, and 1/8 each
of Himalayan and Siberian elms (Florence)
FL493 has one of the highest levels of disease tolerance of any clone produced by the Italian
breeding programme. Its growth is very vigorous, and possibly too vigorous to maintain
stability under some UK conditions. Its form, at least as a young tree, is indistinct. However,
that does not rule out the development of more pronounced character with maturity. It is a
variable tree, very sensitive to its environment. At its best, it is close to traditional European
elm notomorphs such as Huntingdon, to which it is quite closely related.
6. U. minor “Ademuz” (Madrid)
A Spanish selection of U. minor, the field elm, obtained from near Valencia. The very sever
Spanish method of disease tolerance testing suggests that “Ademuz” outperforms the reliably
tolerant hybrid “Sapporo”. Its root activity and girth increments are powerful, which
promises well for performance in the field but makes prolonged cultivation in pots difficult.
The form of the tree is less than ideal, since the junctions between major branches are rather
narrow, and strong shoots growing beneath the leading shoots have a tendency to overtake it.
7. U. minor “Dehesa de Amaniel” (Madrid)
Another Spanish selection of pure U. minor, this clone has exhibited extreme disease
tolerance. Its growth is fairly vigorous and regular in young plants. It is not known how it
performs with increasing maturity. The leaf shape, which is comparatively orbicular, seems
attractive. The angle at which the foliage is held, which actually matters more than leaf shape
in the overall impression of a tree, may be less than ideal.
8. AR 1 (Morfeo x Patriot) (Rochester, Kent)
This English hybridis a reasonably stable tree with a modest growth rate, acceptable form and
an attractive leaf shape. It remains to be seen what disease tolerance it will show upon
inoculation testing, but in view of its parentage it is likely to be significant. Its problem is the
tone of its foliage, which is more pronouncedly grey than its maternal parent, Morfeo, and
seriously restricts its landscape usefulness.
9. AR 2 (Morfeo x Patriot) (Rochester, Kent)
This sibling of AR 1 (above) is a very different tree, displaying greater vigour, possibly less
stability, but none of the greyish tone of the former. Again, its resistance is currently
untested, but is likely to be significant. The problem with AR 2, if indeed it is a problem, is
that at close quarters it is not very reminiscent of European elm at all. It has fully inherited
the more easterly foliage characteristics of its paternal parent, Patriot.
Cont’d
10. FL493 x Patriot (Rochester)
This one of several dozen crosses of this parentage created in 2015. Some including this one
proved insufficiently vigorous to plant out on an inoculation trial site earlier this year, and
were retained in pots for a further season. This plant seems to exemplify a recurrent problem
with the crossing of already complex clones. It looks like the product of an elm “melting
pot”, because that is what it is. Several of this progeny had markedly smaller leaves than
either parent. With complex crossing it seems unusual to obtain seedlings with larger leaves
than either or both parents – no theory is put forward here as to the reasons for this. Disease
tolerance is probably good or very good.
11.FL493 x U. minor “Tonge Mill” (Rochester)
These are two of the least vigorous of this 2015 crossing which produced 82 seedlings in all.
Their appearance is closer to the Tonge Mill male parent than to FL493, showing up in leaf
shape, but above all in the angle at which the foliage is held. The question, which will be
answered in a few years’ time, is whether any of this progeny has obtained any of the disease
tolerance of FL493. If any of them have, they could be useful elms.
David Herling
www.ResistantElms.co.uk
Rochester, Kent, June 2016
Powerpoint Presentations
The 2016 International Elm Conference
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