Report for the Winston Churchill Memorial Trust
Woodland and tree management in the wake of
Ash Dieback (Hymenoscyphus fraxineus):
Experience from Continental Europe
Denmark, France, Germany, Lithuania,
Luxembourg, Sweden and Switzerland.
JOE ALSOP - Churchill Fellow 2014
“To build may have to be the slow and laborious task of years. To
destroy can be the thoughtless act of a single day.” - Winston Churchill
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Contents
Introduction
1
Project Aims
5
Ash dieback in continental Europe
6
Case study 1: Trial plot - Baden-Württemberg, Germany
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Case study 2: Dalby Söderskog National Park, Sweden
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Current Management: Practice & Consequence
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Case study 3: Spreewald Biosphere Reserve, Germany
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Case study 4: Elmias LIFE-Project, Island of Gotland, Sweden
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Case study 5: Forêt domaniale d'Auberive, France
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Conclusion
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Recommendations
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Acknowledgements
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References
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Itinerary
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Introduction
This report has been compiled on behalf of the Winston Churchill Memorial Trust. It
details the findings of a European trip in 2014 to study the serious tree disease, Ash
dieback. Meetings were held with a wide range of industry professionals including
forest pathologists, university research scientists, lecturers, species and habitat
specialists, foresters and site managers. The contents are a summary of what was
learnt and the understanding which was gained, and, where appropriate, this is
supported by relevant references.
The Winston Churchill Memorial Trust ‘funds British citizens, who are resident in the
UK, to travel overseas to study areas of topical and personal interest, to gain
knowledge and bring back best practice for the benefit of others, their profession and
community, in the UK’ (WCMT 2014).
The Significance of Ash______________________________________
The Ash tree (Fraxinus excelsior) has an extensive range throughout Europe, growing
as far East as Russia, throughout Ireland in the West, down to Greece in the South
and its Northern range stretches up into Norway (Euforgen 2010). The species is
important for its great historical, cultural, ecological, biodiversity, economical and
commercial value - possibly nowhere more so than in the UK.
The Ash has long been held in high regard. In old Scandinavian mythology the Ash
was known as the tree of life - ‘Yggdrasil’ (Mabey 1998) - and in the UK, its historical
significance is shown in that there are more places with ‘Ash’ in their name than any
other tree species, except ‘Thorn’ (Marren 2013). Ash occupies a fairly unique niche
within the limited suite of British native tree species, and, further still, in the even
smaller group of native trees which can attain canopy dominance. It coppices well,
can grow in a wide range of sites and, where conditions are optimal, it can grow fast,
producing a pure, off-white, valuable, straight-grained timber which can be worked
easily for a wide range of applications. It is has one of the toughest timbers,
absorbing shock well, making it well suited for tool handles and, where quality isn’t achieved, the timber still commands a good price for its excellent firewood. Ash
regenerates extremely well, has shade tolerant seedlings and, in addition, it is one of
the few hardwoods of timber value to be almost entirely unsusceptible to damage
from the Grey squirrel (Sciurus carolinensis) (Fraxigen 2005). Growth traits make the
Ash an intermediate between a permanent forest component and a pioneer species
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(Pautasso et al 2013) and, in certain conditions, it can excel at both. Ash trees are
usually dioecious, having separate male and female plants, although monoecious
specimens can occur (Harmer, Kerr & Thompson 2010).
In addition to its commercial significance, Ash is also of great biodiversity value,
providing a unique set of ecological traits: – whilst in leaf, the lightly shading canopy
provides conditions for a diverse ground flora, and once the leaves are shed, they
produce a shallow, rapidly degrading leaf litter which is nutrient rich and maintains a
high soil pH. Of the 955 species which use Ash (known as ‘Ash associated species’), 44
of these have been identified as only being found on Ash trees (Mitchell et al 2014a).
Ash is a significant component of the British countryside: it is the second most
frequent individual tree species (after Oak) and is the most common hedgerow tree
(Maskell et al 2013). Ash’s importance within the landscape and for biodiversity has
already been further enhanced by the loss of the majority of Elm trees (Ulmus sp),
due to Dutch Elm Disease (DED). Elm can host a large number of Ash associated
species (Mitchell et al 2014b) and, like Ash, it has a high bark pH. It exhibits comparable
growth traits and performance and grows well in a similar range of site conditions. In
addition, where the bark pH of some tree species has declined due to acidification
over the last century, it may now have rendered them as unsuitable hosts for some
lichen species, which are now more reliant on Ash (Bates & Farmer 1992 & Scheidegger
2014).
In the UK, Ash woodlands are more prominent than they are in mainland Europe
(Peterken 2013) and according to the Forestry Commission (2014), Britain has around
130,000 hectares, making up to 5.5% of the nation’s total woodland cover. With all
this in mind, it is entirely understandable that since 2012, when the presence of Ash
Dieback (Hymenoscyphus fraxineus) was first confirmed in the UK, (in a tree nursery
in Buckinghamshire and shortly after in the wider environment,) foresters,
conservationists, woodland managers and timber growers have all become
increasingly concerned as to what this disease will mean for the future of Ash in the
UK. This concern is further justified as there is no single alternative tree species,
native or otherwise, which can fulfil the unique role of Ash.
Ash Dieback_______________________________________________
Ash Dieback is a serious disease spreading through Europe and affecting the three
native Fraxinus species, most noticeably F. excelsior and F. angustifolia and to a lesser
extent F. ornus. The first symptoms of Ash Dieback were observed in Poland and
Lithuania in the early 1990s, but the cause was initially unknown and wasn’t correctly
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identified until over ten years later. Chalara fraxinea was first identified by Kowalski
(2006) as being the asexual form of the disease but it was initially believed to be
associated with a native saprophytic fungus, Hymenoscyphus albidus, which is a
decomposer of dead fallen Ash leaves. In 2011, Queloz et al correctly identified
Hymenoscyphus pseudoalbidus to be the sexual form of the disease, but, after the
rules relating to the nomenclature of certain fungal species changed in 2011, further
work by Baral et al (2014) declared the correct name for the fungus to be
Hymenoscyphus fraxineus. Interestingly, McKinney et al (2012b) suggests that H.
albidus may be the first extinction, at least locally, to be caused by the invasive
pathogen H. fraxineus.
Ash Dieback has been introduced into Europe from East Asia (Zhao et al 2012), most
likely from the importation of infected trees for planting (Drenkhan et al 2014). In its
native range where it has coevolved with native Fraxinus species, such as F.
mandshurica, H. fraxineus remains harmless. It is unclear whether H. fraxineus has
Joe Alsop, 2014
Figure 1: F. excelsior rachis infected with H. fraxineus - the black staining is symptomatic. Gotland
Sweden.
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become such a serious pathogen in Europe solely because coevolution hasn’t occurred between host and pathogen, resulting in an extremely low levels of
resistance or whether the different climate and phonological sequences are also
factors.
The small cup-fungus fruiting bodies of H. fraxineus grow on the rachis of fallen Ash
leaves (Fig. 1) and release ascospores between June and October. These spores then
alight on living Ash leaves causing infection which then spreads down the rachis and
enters the twigs and stem causing dieback. When these newly infected leaves are
shed, they will produce fruiting bodies the following year, completing the disease
cycle.
In the UK, it can only be assumed that Ash dieback will have a similar impact on the
Ash tree population as it has in continental Europe. With this in mind, it is essential to
gain a good proportional understanding of what this impact will be, and whilst there
has been a lot written and reported on the subject, it doesn’t quite compare with first-hand observations and on-site discussions with tree and woodland specialists.
Joe Alsop, 2014
Figure 2: Ash dieback severely affecting a young stand of F. excelsior in Jura, Switzerland.
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Project Aims
As Europe has up to a 20-year head-start in managing trees and woodland in the
wake of Ash dieback, they have valuable experience of how the disease will spread,
the effect it has on trees and woodland and also any measures which can be
implemented to mitigate against its negative impacts. Whilst the main focus of the
project was to investigate the effect of Ash dieback in woodlands where conservation
is the primary management objective, many such woodlands also have commercial
interests so timber production was also considered.
The aims of the project were to:
1. Learn first-hand about the impacts of the disease on mature trees and
woodlands especially where Ash is a key species.
2. Gain knowledge of management options and techniques which can minimise
the negative effects of Ash dieback on woodland ecosystems and landscapes
in addition to economic and social factors.
3. Learn about how tolerant or resistant strains of Ash can be identified,
propagated and promoted to ensure their survival.
4. Learn how Ash dominated woodlands can be made more species-diverse to
enable them to be more resilient to pests and diseases.
5
Ash dieback in continental Europe
Roy & Kirchner (2000) state, “Host organisms can respond to the threat of disease
either through resistance defences (which inhibit infection) or through tolerance
strategies (which do not limit infection, but reduce or offset its fitness
consequences).” Throughout the range of F. excelsior populations in Europe currently
under infection pressure from H. fraxineus, none have been found to be completely
disease free (McKinney et al 2011, McKinney et al 2012b, Pliūra et al 2011, Pliūra et al 2014 &
Stener 2012). Therefore it is likely that within these populations, rather than true
resistance, there are just differing degrees of tolerance. It is clear that genetics is the
primary factor which determines disease susceptibility (Stener 2012, McKinney et al 2011
& McKinney et al 2012a). In addition, it is important to understand that there are a range
of contributory factors which can also influence survival or mortality, but many of
these are yet to be wholly understood. Infection pressure from H. fraxineus acts like a
war of attrition, and in trees with low levels of tolerance, their energy reserves can
become rapidly depleted fighting the disease. Transversely, it appears that when
subjected to additional biotic or abiotic stress factors, even trees with higher levels of
tolerance can have their ability to resist infection reduced (Bakys, Vasaitis & Skovsgaard
2013). As many of these secondary factors are dynamic, the plight of a tree can
change over time resulting in trees succumbing which at first appeared to be
tolerant, and also trees which are at times greatly affected, later rallying.
Interestingly, many forest professionals commented on the fact that the condition of
F. excelsior could vary from year to year, and in both Sweden and Denmark, they
thought that generally trees appeared to be in better condition in 2014 compared to
previous years (Fig. 3). Similar observations of yearly variation are also reported by
Pliūra et al (2014) and Stener (2012).
Regarding the proportion of the F. excelsior population which is considered to be
disease tolerant, 10% is often quoted, but one first needs to understand what is
actually being classified as tolerant. Assessment protocols can vary from country to
country and trees considered to have some degree of tolerance can range from
having no visible symptoms up to having 35% of the crown affected. Amongst others,
Enderle et al (2014), Metzler et al (2012), Kirisits & Freinschlag (2012), McKinney et al
2011, Stener (2012) all describe methodologies for scoring and classifying tree health
in relation to the levels of damage symptomatic of Ash dieback. As an example,
Enderle et al (2014) suggests classifying dieback and the associated defoliation as a
percentage of the crown affected, e.g. class 0 = no symptoms visible, class 1 = 1-10%,
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class 2 = 11-25%, class 3 = 26-60% and class 4 = 61-99%, and obviously with 100%, the
tree would be dead. Due to some trees which are severely affected by H. fraxineus
producing prolific epicormic growth (figs. 3 & 4), they could score well in this system.
Consequently, Enderle et al (2014) take this into account and also record the level at
which a tree is affected by the disease, by using the same classification system to
estimate the amount of epicormic growth present within the crown. It can be
assumed that the production of epicormic growth is an indicator of disease
susceptibility, whilst the extent of crown defoliation is an indicator of overall tree
vigour (Enderle et al 2014). So a tree with very few shoots and twigs dying back and
otherwise symptomless could be considered to have a good level of disease
tolerance, whilst a tree producing epicormic growth and has extensive dieback would
not be. Throughout the trip, many trees were observed which had clearly been
heavily affected by H. fraxineus in the past, with much of their outer crown having
Gunnar Isacsson, 2009
Gunnar Isacsson, 2014
Figure 3: A severely affected F. excelsior in Norra Sandby, Scania, Sweden. Whilst the tree looks
better in 2014, it can’t be considered to have recovered, nor can it be considered as having a high
level of disease tolerance, due to the secondary ‘inner’ crown which has developed from epicormic stress growth. What the pictures do show is the variation in tree health which can occur from year
to year.
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Joe Alsop, 2014
Figure 4: A F. excelsior in Skåne county, southern Sweden, which has suffered severe levels of
dieback in the crown and is now developing a secondary, inner crown from stress induced
epicormic growth.
died off and they had subsequently produced a secondary inner crown from stressrelated epicormic growth. Whilst such specimens had managed to endure the disease
and in some instances ‘rally’, the opinion of many professionals suggests their longterm prospects aren’t positive. At best, the conclusion from studies by McKinney et al
(2011) and Pliūra et al (2011), estimates 2-5% of the Ash population will remain
unaffected by the disease, whilst Kjær et al (2011) believe that under current
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infection pressure, only 1% have the potential of producing tolerant offspring and
even then they will be expected to have up to 10% of their crowns damaged by Ash
dieback.
It is worthwhile remembering that historically, prior to the arrival of H. fraxineus, F.
excelsior was often seen to exhibit a range of symptoms very similar to those now
associated with Ash dieback. Ash is very sensitive physiologically to temperature,
especially severe winter or late spring frosts (just prior to or during bud-flushing), and
such occurrences can affect foliage and branches causing similar effects to dieback
(Dobrowolska et al 2008, Evans 2014, Fraxigen 2005, Kerr 1995 & Savill 2013). Variations within
populations due to such temperature-related effects are likely caused by
phonological variation (Evans 2014). Female trees can often suffer dieback symptoms
on branches which have borne seed the previous years, especially after heavy mast
years, whilst mild winters can sometimes fail to break dormancy, resulting in sparsely
foliated trees during the growing season. Periods of water stress, especially drought,
can also result in dieback within the crown (Dobrowolska et al 2008). Kirisits et al (2008)
report that many such factors were initially thought to be the cause of Ash dieback
during the early 1990s in Poland. A condition also known as ‘Ash dieback’, causing similar yet not as widespread or severe symptoms as H. fraxineus, is referred to by
Hibben & Silverborg (1978) and Strouts & Winter (1994).
Environmental Conditions___________________________________
Trees growing in sub-optimal conditions are often subjected to a greater number of
biotic and abiotic stresses and as such, site conditions are an important secondary
factor in determining Ash tree survival when under infection pressure from H.
fraxineus. The optimal site conditions for F. excelsior are typically in calcareous loams
which are deep, fertile, moist yet freely-draining and pH (7-8) neutral (Dobrowolska et
al 2008 & Savill 2013). Site conditions, such as soil moisture, are dynamic and can be
influenced by a wide range of factors, and changes to stand structures through
disease or harvesting can have a significant effect (Pike et al 2010). Ash is sensitive to
drought or water-logging (Dobrowolska et al 2008 & Fraxigen 2005) and such stresses can
make trees more susceptible to and more severely affected by Ash dieback (Bakys,
Vasaitis & Skovsgaard 2013, Cech & Hoyer- Tomiczek 2007, Kenigsvalde et al 2010 & Lemoine,
Peltier & Marigo 2001).
Periods of ground moisture deficiency or drought which can be caused by strong
competition within dense stands, have both been linked to predisposing trees to the
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disease (Bakys, Vasaitis & Skovsgaard 2013, Cech & Hoyer-Tomiczek 2007 & Lygis et al 2005).
Trees in very wet conditions or subjected to sustained water-logging have also been
shown to be more susceptible (Bakys, Vasaitis & Skovsgaard 2013 & Kenigsvalde et al 2010)
and their rate of decline can be more rapid compared to drier sites (Metzler et al 2013).
Due to Ash being a light-demanding species beyond the stand initiation stage
(Dobrowolska et al 2011, Fraxigen 2005 and Harmer, Kerr, & Thompson 2010), competition
for light can also reduce vigour and consequently increase the severity of Ash dieback
in dense stands (Bakys, Vasaitis & Skovsgaard 2013 & Keßler et al 2012).
Phenotype & Vigour________________________________________
The local environment, site conditions and genotype can all influence a tree’s
phenotype and/or levels of vigour and these physical factors can play an important
role in dictating disease tolerance. Throughout all the countries visited, trees which
exhibited few or no obvious symptoms of Ash dieback were almost exclusively prime
specimens (case study 2). Specimens which are suppressed, lacking in vigour, slow
growing or of average or below-average size often seem more susceptible to Ash
dieback, indicating that disease tolerance is reduced in trees with decreased growth
potential or vigour (Bakys, Vasaitis & Skovsgaard 2013, Cech & Hoyer-Tomiczek 2007, Enderle et
al 2014, Lobo et al 2014, McKinney et al 2011, Skovsgaard et al 2010 & Stener 2012). In addition,
it is apparent that bud burst phenology can also affect disease susceptibility, in that
phenotypes which come into leaf earlier and shed sooner, are often less affected by
Ash dieback (Bakys, Vasaitis & Skovsgaard 2013, McKinney et al 2011, Pliūra & Baliuckas 2007, Pliūra et al 2011, & Stener 2012). This could be in part due to the younger, less welldeveloped leaves of later-flushing phenotypes being more susceptible to infection
(Bakys, Vasaitis & Skovsgaard 2013), and the longer presence of leaves on a tree
providing the disease with an extended period to cause infection (Bengtsson et al 2014
& Kirisits, Krautler & Cech 2010).
Infection Pressure__________________________________________
Within a local environment, the level of infection pressure is an important factor in
influencing the severity of Ash dieback. Throughout Europe, Ash trees can be
observed which appear in good health, with little or no symptoms visible, but unless
such trees are within an area of known infection pressure (Fig. 5), e.g. there are other
trees within the locality which are either dead or dying and obviously suffering from
the effects of H. fraxineus, then their apparent tolerance cannot be relied upon. It is
logical to think that in areas with high population densities of Ash trees, there will be
an increased capacity for the production of H. fraxineus fruiting bodies and, in turn,
10
increased spore-loading (Ennos 2015). Infection pressure can change from year to year
(Chandeliera et al 2014) and as growth and sporulation of H. fraxineus is favoured by
high levels of air and soil moisture and humidity (Dal Maso & Montecchio 2014, Gross et al
2012 & Kirists et al 2012), the seasonal variation of weather, in conjunction with site
conditions, can in turn, have a significant effect on infection pressure. Weather
conditions may even influence which circumstances are most suitable for leaf
infection by H. fraxineus (Enderle et al 2013). Spore densities have been shown to be
consistently higher at distances of 0.5m from the ground than they are at 3m
(Chandeliera et al 2014), and as younger and smaller trees are often more severely
affected by Ash dieback (Kirisits et al 2011, Keßler et al 2012, McKinney et al 2011 &
Skovsgaard et al 2010), this could well be a factor. A recent Austrian study has shown
that F. excelsior rachis can produce H. fraxineus ascocarp for a period of up to five
Joe Alsop, 2014
Figure 5: A healthy Ash surrounded by other severely affected specimens, representing a good
indicator of infection pressure from H. fraxineus: Gotland, Sweden.
11
years, although abundant production usually only occurs in the first two years of
infection (Kirisits, Kritsch & Krautler 2014). Fruiting body formation has also been found
to occur on small twigs and, whilst this seems uncommon, it is more likely to occur in
moist conditions (Kirisits et al 2012 & Kirisits, Kritsch & Krautler 2014). Climatic conditions
can influence fruiting body and spore production with incidences and areas of high
humidity favouring high levels of both (Boddy et al 2014 & Kirisits et al 2012).
There are some suggestions that the effects of the disease are reduced in Ash stands
with dense sub-canopy understoreys (especially evergreen), either due to a more
stable microclimate and soil moisture regime by reduced evapotranspiration
(Skovsgaard 2013) or by the simple formation of a physical filter for spores, resulting in
large numbers of them attaching to non-host species.
Root and Collar Rot_________________________________________
In areas under infection from H. fraxineus, many trees also suffer from a range of
symptoms within the base of their stem, root collar or root system (Bakys et al 2011,
Enderle et al 2013 & Lygis et al 2005). It is unclear whether the development of basal stem
lesions (Fig. 6) and aerial root infections are caused by H. fraxineus spores infecting
trees via the bark lenticels (Husson et al 2012), whether they are a symptom of
Armillaria infection (Lygis et al 2005), or whether they represent an interaction
between the two species (Enderle et al 2013 & Husson et al 2012). In addition, a number
of sites visited on this research trip displayed trees with few or no crown symptoms
present, yet showed signs of root and/or collar rot - this is in accordance with the
observations of many specialists, and also Bakys et al (2011), Enderle et al (2013) and
Lygis et al (2005). It is therefore likely that if such damage is caused by H. fraxineus,
tolerance within the crown and to these necrotic basal lesions does not necessarily
correspond with each other (Enderle et al 2013). In addition, Enderle et al (2013) and
Husson et al (2012) state that moist soil conditions proved favourable for the
development of bark collar lesions and this certainly tallied with many sites visited on
the trip (case study 1). Metzler et al (2013) and Bakys et al (2011) report that the
accelerated rate of decline which is often experienced in wet sites could possibly be
due to the prevalence in such sites of additional root infections (Fig.7). Trees under
stress have a significantly increased risk of infection from Armillaria spp (Wargo & Shaw
1985), and prior to Ash dieback, it was uncommon for F. excelsior to act as a host for
Armillaria spp (Lygis et al 2005). However, Armillaria infections are now highly
associated with Ash trees suffering from H. fraxineus (Bakys et al 2011, Enderle et al 2013,
Husson et al 2012 & Skovsgaard et al 2010). Whilst occurrences of Armillaria on F. excelsior
12
A
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B
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C
Joe Alsop, 2014
D
Joe Alsop, 2014
Figure 6: A range of symptoms and effects of basal stem lesions, root rot and Armillaria infection.
A: A well-developed elongated lesion on F. excelsior, note the brown coloured bryophyte at the
left-hand-side base – this was common on trees with stem lesions: Jura, Switzerland. B: Extensive
bark necrosis and the associated white mycelium of Armillaria spp on a F. excelsior: Jura
Switzerland. C: A felled tree showing the typical areas of decay associated with necrotic basal stem
lesions: Skåne county, Sweden. D: Armillaria fruiting bodies at the base of a F. excelsior: north-west
Lithuania.
are classed as secondary infections (Bakys et al 2011 & Lygis et al 2005), they have the
potential to increase the rate of tree decline significantly when in combination with
H. fraxineus (Bakys et al 2011 & Husson et al 2012). It seems likely that, on sites where
13
Armillaria is already present yet has historically led a latent existence alongside F.
excelsior, the arrival of H. fraxineus can somehow trigger the fungus to become
pathogenic (Lygis et al 2005). Armillaria cepistipes and A. gallica have been shown to be
the main protagonists (Bakys et al 2011, Enderle et al 2013, Husson et al 2012, Lygis et al 2005
& Skovsgaard et al 2010) but not necessarily all sites will have such Armillaria spp
present (Bakys et al 2011 & Husson et al 2012). Whilst in the majority of instances the
severity of the collar and root rot correlates with symptoms within the crown, this is
not always the case (Husson et al 2012). Some trees can show few symptoms within the
crown yet still be affected by collar rot (Enderle et al 2013). In some sites, young trees
(approximately 20 years old) with live crowns could be pushed over by hand due to
their damaged root systems. In Germany it was revealed that a forest worker had
been killed by a falling Ash with such an unobvious defect.
Joe Alsop, 2014
Figure 7: A heavily affected 40 year old F. excelsior plantation in the floodplain forests of the Rhine
valley, Baden-Württemberg, Germany. Ash dieback arrived in 2007. Currently, less than 5% of the
trees were showing a good level of disease tolerance and, throughout the stand, secondary
infection by Armillaria spp was much in evidence.
14
A
Joe Alsop, 2014. B
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Figure 8: A good demonstration of the severe pressure which F. excelsior endures under infection
from H. fraxineus - Ash has to be extremely stressed to produce epicormic growth like this. A: The
crown of this Ash was a profusion of epicormic growth: French-Swiss border. B: Open grown
roadside Ash (approx. 80cm dbh, 20m in height) which have succumbed to ash dieback after
enduring the disease for less than five years: French-Swiss border.
Summary of key knowledge __________________________________
 Whilst a tree’s genotype is the primary factor dictating its survival or mortality, secondary factors can also have an influence and in some instances could
predispose trees to the disease or transversely afford them an increased
chance of survival.
 No trees have been found to be resistant: they just have varying degrees of
tolerance. Trees with less than 25% of their crowns affected make up
approximately 10% of the population, whilst trees possessing the highest levels
of disease tolerance comprise only 1-5%. Even these can have up to 10% of
their crowns affected. Trees with more than 50% of their crowns affected
stand little chance of survival and there can be no certainties either way with
trees showing between 25% and 50% of their crowns affected.
15
 Not all trees will die immediately: trees with low to medium levels of disease
tolerance can endure the disease for a number of years, often producing
profuse epicormic growth or temporarily ‘rallying’ with the development of
secondary ‘inner’ crowns.
 The severity of symptoms and associated tree health are subject to seasonal
variations and such variation can also occur between different countries.
 Supressed trees of poor vigour or those growing in sub-optimal site conditions
are often more severely affected but if a tree’s genotype provides no disease tolerance, then even vigorous, prime, un-stressed specimens, growing in
optimal conditions won’t survive.
 Tolerance can only be measured over a number of years within areas which are
under obvious infection pressure and the health of trees which at first appear
to be tolerant can and are often seen to steadily decline.
Joe Alsop, 2014
Figure 9: A line of F. excelsior on the roadside near Dijon, eastern France. Ash dieback arrived in
2009 and this group of trees shows the severe stress they are under. Some are dead but the
majority of them have prematurely shed their foliage in reaction to the infection pressure from H.
fraxineus. The picture was taken on 06.09.2014.
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Case Study 1: Trial plot - Baden-Württemberg, Germany.
Visited on 27.08.2014 and hosted by Berthold Metzler, Forest Pathologist
of the FVA Research Institute of Forest Management.
Planted in 2005, with two-year-old plants from a range of local provenance
genotypes, this trial plot was established to investigate tree tolerance to
flooding and water logging. Ash dieback was first confirmed in 2009 and
monitoring the effects of the disease in the plot was also started at that time. By
July 2014, the disease associated mortality rate was 12.5%. The site receives 722
mm of rainfall per annum, its soil ranges between pH 4.2 (at 150mm) to 9.0 (at
900mm), it lies at an elevation of 173m and is located at 48°11’ N, 7°42’ E.
Due to disease monitoring since 2009, the plot provides a good demonstration
of how H. fraxineus can develop over a period of time. Fluctuating tree health
A
Joe Alsop, 2014 B
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Figure 10: A: A good example of where the apical shoot has suffered dieback (still attached
and just visible) and the tree has survived for a time, allowing lateral side branches to assume
co-dominance. The dead leaves still attached show that the tree died during that growing
season (2014). B: Another example of where the apical shoot has died and a lateral branch
has assumed apical dominance.
17
Case Study 1: Continued
and the associated range of disease tolerance within different genotypes, was
highly evident, e.g. some trees can succumb almost immediately, some can
endure the disease for a number of years but then die, others appear greatly
affected at first then rally but can then also succumb, a small portion can suffer
dieback of their apical shoot but survive (Fig. 10) although still suffering dieback
symptoms and many specimens are affected by necrotic bark collar lesions (Fig.
11). Within the plot, all trees were displaying some symptoms and very few
specimens were exhibiting currently high levels of tolerance. In addition, the
poor physical appearance of the stand was exacerbated by the premature leaf
shedding of many trees - a reaction to the infection pressure from H. fraxineus
spores (Bakys et al 2009, Kirisits, Krautler & Cech 2010 & Stener 2012 ).
A
Joe Alsop, 2014 B
Joe Alsop, 2014
Figure 11: A: F. excelsior showing the typical dark staining at the base on the left-hand side,
which is symptomatic of a collar rot lesion. B: The same tree with the area of necrotic bark
removed to reveal the distinctive white mycelium fans of Armillaria. The tree has been almost
entirely girdled by the collar rot.
Key findings:
 There is a wide range in levels of disease tolerance between genotypes.
 Some trees can survive initial infection and in some cases fight the
infection for a number of years but succumb at a later time.
 Trees with live crowns can have severe and ultimately terminal collar
lesions and rot present.
 Sites with higher soil moisture content have a greater number of trees
affected by collar lesions and rot.
18
Case Study 2: Dalby Söderskog National Park, Sweden.
Visited on the 21.08.2014 and hosted by Jörg Brunet, Professor in Ecology at the
Swedish University of Agricultural Sciences (SLU).
Despite its National Park status, the 37 ha of mixed broadleaf woodland which
makes up Dalby Forest is more akin to a Nature Reserve. Prior to receiving
National Park status in 1918, Dalby had a long management history as wood
pasture: grazing ceased sometime before designation and, since then,
management has been limited intervention. The site is designated for four
different Natura 2000 woodland habitat types, (91E0) Alluvial forests and (91F0)
Riparian mixed forests being where F. excelsior is a notable species. The site has
a rich ground flora and hosts a number of Red Book listed species, including
bryophytes, saproxylic beetles and flies and vascular plants. The calcareous soils
have an average pH of 6.1. The site receives 650mm of rainfall per annum, lies
at 55◦41’ N, 13◦20’ E and is between 50–75m above sea level (Brunet et al 2014).
Prior to DED, Ulmus glabra was the most common species in Dalby, but since
the 1990s, Ash has taken over as the most abundant tree species and currently
comprises one third of the canopy cover. Other tree species present include
Acer platanoides, Alnus glutinosa, Fagus sylvatica, Populus tremula, Quercus
robur and Tilia cordata. The presence of Ash dieback was first confirmed in
Dalby in 2005, and within six years, approximately 60 % of Ash trees were
damaged by the disease and 5% were dead (Fig. 12).
Figure 12: Dalby Söderskog survey data from 2011 showing the percentage of Fraxinus
excelsior stems, in various dbh-classes and classified as either healthy, damaged by disease or
dead. Total number of surveyed stems is given above each bar (Brunet et al 2014).
19
Case Study 2: Continued
Unlike many of the other forests visited in Europe, where timber production
was a concern and dead and dying Ash trees had been harvested, the minimal
intervention management policy at Dalby provided a unique opportunity to
study the full range of effects from Ash dieback and how they have developed
over time. In addition, Dalby gives a good representation of how a broad range
of trees growing in varying site conditions, of different phonological types,
rates of vigour, size and age classes are all being affected by H. fraxineus.
Within the woodland, Ash trees in mixed stands did have larger crowns and
better vigour, whilst in the more Ash dominated stands, the trees, obviously
having competed from seedling stage, had smaller crowns. Where normally the
highly competitive Ash regeneration would outcompete other tree species, due
to the majority of this now dying, it is allowing greater numbers of Q. robur
seedlings to establish.
A
Joe Alsop, 2014
B
Joe Alsop, 2014
Figure 13: A: Ash (approx. 50cm dbh, 19m in height) which were growing in a wet part of the
site, now succumbed from the effects of H. fraxineus. B: The largest F. excelsior specimen in
Dalby (approx. 115 cm dbh, 24m in height) which appeared in good health displaying
minimal symptoms of Ash dieback.
20
Case Study 2: Continued
Key findings:
 In comparison to larger crowned, more vigorous specimens, trees with
less vigour and small, poorly-developed crowns appeared to be suffering
more from the effects of Ash dieback.
 Trees in more water-logged areas of the site were significantly more
affected by Ash dieback in comparison to freer draining areas.
 Symptoms of secondary infection by Armillaria spp were highly prevalent
in water-logged areas.
 The large-scale loss of Ash as a canopy dominant looks likely to favour Q.
robur and F. sylvatica as replacements in the future (Brunet et al 2011).
 With U. glabra numbers already seriously depleted by DED and Ash now
at risk from H. fraxineus, the substantial loss of suitable bark habitat for
associated epiphytic species has been and will be exacerbated.
 In 2010, in Sweden, F. excelsior was added to the red data book list of
threatened species (Bengtsson et al 2014).
21
Current Management: Practice & Consequence
The initial confusion regarding the cause of Ash dieback coupled with its invasive
nature and the rapid pace with which it has spread throughout Europe, has, in many
instances, left little time to trial or develop effective silvicultural strategies to
alleviate its effects. In addition, in many forests where timber production is an
objective, salvage felling has further reduced the possibility to do so.
Joe Alsop, 2014
Figure 14: A badly affected stand of F. excelsior approximately 80 years of age: Gribskov, Denmark.
Since H. fraxineus arrived in 2003 the stand has received a heavy thinning, felling dead and diseased
trees in an attempt to salvage timber revenue. Tolerant trees were retained but the health of many
of these has subsequently declined.
Clearance_________________________________________________
In some parts of Europe, large quantities of Ash have been cleared, such as in
Denmark where many stands have been felled in an attempt to prevent loss of
timber value (Kjær et al 2011) or as in Lithuania where sanitary felling, in an attempt to
22
slow disease-spread, has decreased the country’s Ash forests by nearly a third (Lygis et
al 2013). In the sites where heavy salvage-felling or thinning operations had taken
place, trees had been retained which at the time of felling had shown good levels of
tolerance. In many instances the health of these retained trees had subsequently and
dramatically declined (Fig. 14 & case study 3). In a study by Bakys, Vasaitis &
Skovsgaard (2013), they found that dieback symptoms were more frequent in heavily
thinned stands. Heavy thinning and clear-felling operations have been shown to have
a sudden and significant impact on soil moisture and compaction - increasing both
(Castro et al 2000, Dannenmann et al 2007, Sundqvist et al 2014, Wu et al 2011 & Yoho 1980).
Whilst it was widely reported that the general health of Ash trees, even those which
appear at first to have good levels of disease tolerance, is steadily deteriorating over
time (Enderle et al 2014, Lobo et al 2014, Pliūra et al 2014 & Pliūra et al 2011), it is likely that
the sudden change in site conditions, particularly the stability of the soil moisture
regime, has further stressed these retained trees, accelerating their decline.
Thinning__________________________________________________
As discussed, the heavy thinning of stands to salvage dead and diseased trees can
have additional negative consequences, but the adoption of a more structured and
targeted approach could alleviate disease effects in some stands. A study by Bakys,
Vasaitis & Skovsgaard (2013) found that within young Ash dominated stands, disease
severity was greater in un-thinned control plots compared to thinned ones and whilst
the reasons for this may not be entirely clear, they do suggest that strong
competition for light and resultant decreased vigour has at least contributed. As
previously mentioned, F. excelsior has a critical phase within tree and stand
development when it switches from being shade tolerant to significantly more light
demanding (Dobrowolska et al 2008, Dobrowolska et al 2011, Fraxigen 2005, Harmer, Kerr, &
Thompson 2010 & Savill 2013). Work carried out by Skovsgaard et al (2010) highlights this
stage (i.e. the period from trees being too tall for formative pruning and up to the
point where they have trunks of sufficient commercial interest,) as being the optimal
time for conducting thinning operations to mitigate the severity of Ash dieback.
Despite the additional need to consider Ash dieback, it is already established that
once Ash reaches a height of 6-7m it requires frequent thinning to promote vigour
and maintaining a crown over at least one third of the height of the tree is
recommended (Kerr 1995). Thomsen & Skovsgaard (2012) and Ahlberg (2014) agree
that in stands which are greatly affected and have low tolerance to Ash dieback,
thinning will have little effect on minimising its impact (case study 5), although
23
thinning to promote healthy, tolerant Ash, irrespective of their age, to minimise any
additional stress factors would seem a prudent measure.
Joe Alsop, 2014
Figure 15: A very badly affected stand of F. excelsior showing the severe loss of canopy cover which
can occur where Ash is dominant. The trees are a mixture of dead, dying and defoliated - all were
affected: Luxembourg.
Ash Dominated Stands______________________________________
Within some woodlands, the loss of small stands or groups of Ash might be beneficial
through the creation of temporary open spaces, glades and areas for natural
regeneration. However, where Ash is dominant or comprises a significant proportion
of the canopy, high rates of mortality or the clearance of large numbers of trees is, at
least in the short term, having the greatest effect through the loss of canopy (Fig. 14
& 15), resulting in a degradation of forest conditions and ecosystem dynamics (Ellison
et al 2005, Kjær et al 2011, Loo 2009 & Pautasso et al 2013). Throughout Europe, such
instances of stand collapse are in many cases exacerbated by the drastic decrease in
successful natural regeneration, growth and establishment of young Ash (Bakys et al
2011, Lygis et al 2013, Pliūra et al 2014 & Stener 2012 and case study 5). Whilst little can be
24
done immediately to maintain canopy control in stands suffering from very high
mortality rates, in stands showing higher levels of disease tolerance the retention of
even moderately healthy trees could play a role in maintaining forest conditions and
aid future stand management (Enderle et al 2013). Thomsen & Skovsgaard (2012) also
suggest that within severely affected stands, maintaining infected trees as shelter
would be beneficial for under-planting to be carried out.
Irregular Mixed Forests______________________________________
The general consensus of all the forest professionals met with on this trip, was that
Ash trees within mixed woodlands were no less symptomatic or affected by the
disease than those within more Ash dominated woods and no studies are known
which counter this. Although it is worth mentioning the obvious, that within single
species, Ash dominated stands, the effects were far more visually apparent than they
were in mixed stands. In addition, many Ash dominated stands, for example in
Denmark, were planted in sites which could be considered sub-optimal on the
account of their very wet conditions (Skovsgaard 2013), and any perceived increase in
disease severity was more likely contributable to site conditions rather than species
composition.
When compared to even aged single species Ash stands, mixed woodlands managed
under irregular silvicultural practices were obviously far less affected by the loss of
Ash trees either as regeneration and/or from the canopy (case study 5). Within such
forests the presence of different species and age classes clearly allowed them the
option to swiftly adapt to the declining Ash population to maintain forest conditions.
Pollards & Coppice_________________________________________
While no forests were visited on this trip where F. excelsior was specifically managed
as coppice, the effects of Ash dieback on coppiced Ash stools can be observed
throughout Europe (Fig. 16). Studies have shown that coppice regrowth is severely
affected by Ash dieback and although this is primarily due to spore infections from H.
fraxineus, the impact from Armillaria decay was also found to have an additional and
significant negative effect (Bakys et al 2011 & Lygis et al 2013). In comparison to natural
regeneration, coppice regrowth often appears to be even more severely affected, but
this is most likely due to healthy regeneration having been produced by tolerant
breeding stock, whilst highly susceptible coppice has probably grown from less
tolerant genotypes (Lygis et al 2013).
25
Of the countries and sites visited on the trip, Sweden and in particular the island of
Gotland had the largest population of pollarded Ash and experience there suggested
that pollard trees faired a little better than coppice but were often more affected
than standards (case study 4). A report by Bengtsson, Stenström & Finsberg (2013)
also indicated that recently pollarded trees were more affected than maidens and
non-recently cut pollards, although further work may have now found the contrary
(Bengtsson 2014). Clearly there is more work needed to understand Ash dieback in
relation to pollard trees but as the cutting of pollards can exert significant stress
(Ferrini 2006) a conservative approach of staging the work and monitoring how a tree
responds would seem sensible.
Joe Alsop, 2014
Figure 16: Coppice regrowth of a F. excelsior severely affected by Ash dieback: Gotland, Sweden.
26
Individual or Specimen Trees of High Value_____________________
Whilst not feasible on a large scale, in some instances a more intensive approach may
be required in order to maintain trees which have a significant and/or specific value.
Although the full report was not available at the time of writing, researchers in
Sweden are working on a project to examine the effectiveness of pruning infected
trees to maintain their vitality and minimise the associated effects of Ash dieback.
Initial indications suggest that this practice could be an effective tool for the
management of important individual trees, such as high value specimens of genetic,
cultural, historic, landscape or ecological significance. Results and more information
should be available later in 2015.
Ash dieback has the potential to rapidly cause the extinction of Ash associated
epiphytic taxa, such as lichens (Jönsson & Thor 2012). In instances where severely
affected trees which are unlikely to survive host lichen species of conservation
concern, the trialling of transplanting these species to healthy surrogate trees could
be carried out (Scheideggar 2014). Scheideggar, Frey & Zoller (1995) report such
practice, as an effective method for aiding the conservation of some lichen species
and carried out successful transplanting of Lobaria pulmonaria on F. excelsior. Whilst
such practice is labour intensive and not guaranteed success, in areas with rare Ash
associated lichens, especially obligates, are suffering high rates of tree mortality, it
may be the only short term option for their population continuity and certainly worth
a try.
Regeneration______________________________________________
The ever diminishing Ash population, either from the disease or felling, is having a
serious impact on the species regeneration potential (Lygis et al 2013). In addition to
this loss of sufficient healthy seed-bearing trees, Ash regeneration, and that of other
species for that matter, is being further hampered where canopy cover has been
severely depleted. In many cases, larger Ash dominated stands suffering from high
mortality rates, or which have been subjected to heavy thinning or clear-felling
operations, have subsequently experienced a major increase in highly competitive,
coarse ground vegetation (Fig. 17). Ash seedlings can easily be smothered by
competing weed growth after the removal of the parent crop and weed control is
considered essential for successful establishment (Kerr 1995 & Savill 2013). To
compound matters further, in areas where Ash does regenerate the mortality rate of
seedlings and saplings is phenomenally high (Lygis et al 2013) and in some sites none
were surviving (case study 5). H. fraxinea has also been found present in the seeds
27
Joe Alsop, 2014
Figure 17: Swiss researcher Valentin Queloz barely visible in a severely affected Ash stand where
canopy control has been lost, resulting in the profuse growth of coarse and highly competitive
ground vegetation: Jura, Switzerland.
of F. excelsior, although the effect of this on germination and seedling growth is
currently unknown (Cleary et al 2012). In areas where the natural regeneration of Ash
28
once prevailed, its replacements vary and are determined by the site conditions and
any other present species. The prospect for natural regeneration of tolerant
genotypes is reliant on maintaining sufficient quantities of healthy seed-producing
trees - the severe reduction of which proves a significantly limiting factor for future
Ash tree recruitment (Kirisits & Freinschlag 2012, Lygis et al 2013, Metzler et al 2013, Pautasso
et al 2013 & Pliūra et al 2011). In addition, in areas where only a small percentage of
trees display effective disease tolerance and are capable of reproduction, population
collapse is highly likely (McKinney et al 2011). In light of the various factors affecting the
natural regeneration of Ash, the long-term prognosis is that in many areas, the future
of the species is seriously jeopardized (Bakys et al 2011 & Enderle et al 2013).
Joe Alsop, 2014
Figure 18: A mixture of dead, dying and currently healthy F. excelsior natural regeneration: Dalby,
Sweden. Many saplings are effectively coppiced by the disease, re-growing after the loss of their
apical shoot, but after repeated reinfection they soon lose vigour and die. The purple and orange
tinged colouring of the stems is highly symptomatic of the necrosis caused by H. fraxineus.
Deadwood________________________________________________
Whilst Ash dieback has clearly given rise to a much increased availability of Ash trees
for both standing and fallen deadwood habitat, the rate of decomposition has in
some cases been greatly accelerated resulting in a relatively short-lived resource.
Secondary infection from Armillaria causing severe root rot and predisposing trees
more easily to wind throw, in addition to infestations by bark beetles and the
29
subsequent feeding activity from avian sp, was rapidly degrading the micro-habitat
and lifespan potential of this deadwood resource. Where dead trees of significant
biodiversity value are desired to be kept standing for as long as possible it may be
prudent to reduce their canopy and associated sail, especially in areas with high
incidences of root decay and/or Armillaria.
Timber Quality & Yield______________________________________
Whilst Ash dieback can significantly reduce diameter increment within infected trees
(Enderle et al 2013, Lobo et al 2014 & Metzler et al 2012), this has been shown to typically
occur in specimens where substantial parts of the crown are affected, i.e. ≥50%
(Enderle et al 2013 & Lobo et al 2014). Trees displaying these levels of symptoms will have
had their energy producing potential severely depleted and will expend their
remaining energy on producing epicormic growth (Lobo et al 2014). In one site in
southern Sweden, a disc cut from an Ash (Fig. 19) clearly showed that more
Joe Alsop, 2014
Figure 19: A disc cut from an F. excelsior by private forest owner John Nordqvist: south-west
Sweden. H. fraxineus arrived in 2001 and has reduced the annual increment for a number of years,
although since 2007 it has grown well. The appearance of the tree was monitored by the owner and
whist it did defoliate moderately in the first years of infection, subsequent symptoms alleviated
matching the story from the annual rings. Of note the tree wasn’t felled due to the disease. tolerant trees can put on good growth increment. In addition, loss of timber quality,
in particular staining, will most likely only occur in severely affected trees, especially
those which produce epicormic shoots from the stem (Skovsgaard et al 2010).
30
Discolouration will also occur in the base of trees where basal lesions and/or
Armillaria are present (Fig. 6C) (Skovsgaard et al 2010 & Thomsen & Skovsgaard 2012).
Alternative Species & Diversification___________________________
In comparison to their continental counterparts, British woodlands are often
comprised of fewer native tree and shrub species (JNCC 2014). In addition, natural
woodlands on limestone, which are completely dominated by Ash (such as those of
the Derbyshire Dales), appear to be uniquely confined to Britain (JNCC 2014). It is clear
that in the majority of cases woodland managers on the continent often have the
distinct advantage of having a greater choice of native tree species present within
their woods to replace Ash (case studies 2 & 5), although in some sites the availability
of alternative species was more restricted (case studies 3 & 4).
In some woodlands with minimal or non-intervention policies (case study 2 & 3),
natural processes will be allowed to prevail and management practice is unlikely to
change, whilst in other forests Ash will be missed, especially where timber
production was an interest, and no more so than in wetter sites where it has often
been promoted or planted. In such areas, the options are limited and most
practitioners were likely to choose Q. robur in the not-so-wet soils and A. glutinosa
elsewhere, although compared to F. excelsior both of these species come with
different silvicultural characteristics, requirements, strengths and weaknesses. In
some sites, A. glutinosa was compromised as a replacement because of Phytophthora
and owing to their requirements for adequate light, during their establishment
phase, site conditions were not always suitable for Quercus sp. Where ground
conditions were stable and not waterlogged or too dry, F. sylvatica was often being
sought as a replacement, and where suitable clay soils allowed, Carpinus betulus was
an option. The effect of DED was variable through Europe and in some areas Ulmus
sp were still viable contenders as canopy forming replacements for Ash, especially in
well drained conditions, along with the ever-present, yet often restricted, T. cordata
and T. platyphyllos. In some sites, lesser species such as Torminaria torminalis
(previously Sorbus torminalis - Savill 2013) and Populus tremula were also being
promoted. Whilst it has become naturalised within many parts of Europe and now
covers a wide biogeographic range, Acer pseudoplatanus is not native throughout
(Hein et al 2009), for example in the Scandinavian countries, northern Germany, much
of the Netherlands and north and western France (EUFORGEN 2008). In addition, where
it does grow naturally, it seldom dominates and is actually relatively scarce, only
occupying a small proportion of the European forest area (Hein et al 2009). Despite this
31
A. pseudoplatanus has comparable silvicultural traits to Ash, growing well in a similar
range of soil conditions and capable of rapidly colonising canopy gaps, yet it is less
site specific and more tolerant of frosts (Savill 2013). Therefore, where A.
pseudoplatanus does grow in conjunction with F. excelsior, it is likely that it will be
allowed to fill its void (case study 5), especially as, unlike in Britain, its potential is not
threatened by the presence of S. carolinensis (Savill 2013).
Joe Alsop, 2014
Figure 20: In stands where Ash was often the species of choice but have now suffered from its loss,
the remaining canopy cover is used for control and under-planting with alternate species is being
carried out: Rhön Biosphere reserve, Bavaria, Germany.
In sites where desirable alternative species were present and suitable conditions
allowed, natural regeneration was often the favoured option for replacing Ash and
within mixed woodlands managed under close to nature principles, this was easily
practicable (case study 5). In areas where species choice was more limited and/or
natural regeneration not so readily available, planting was either being undertaken
(Fig. 20) or considered (case study 3 & 4). Regardless of the stand regeneration
method favoured, the choice of alternative species was nearly always made using a
sound site-based silvicultural approach, even where species choice was additionally
influenced by its commercial potential (case study 5). It would seem logical that in
woodlands where the future of Ash is jeopardized, this practice, in conjunction with
32
cross-referencing with the work of Mitchell et al (2014b), would offer the most
judicious approach for their future management in the wake of Ash dieback.
Breeding Programmes
________________________________
Work by Enderle et al (2014), cite that as F. excelsior can produce upwards of 100,000
saplings per hectare, hopes should be maintained that sufficient quantities of
tolerant trees with adequate genetic diversity will be available either through
conventional selection, or more quickly through breeding programmes. Although
within wild populations, to avoid genetic bottlenecking, large population sizes will be
required (Kjær et al 2011) and as the relative number of tolerant trees within some wild
populations is so low (Stener 2012) and also varies from country to country, this may
not always be feasible. In light of this, the development of breeding programmes will
be an essential tool for the future conservation of F. excelsior (Kirisits & Freinschlag 2012,
Kjær et al 2011, Lygis et al 2013, Metzler et al 2013, McKinney et al 2011, Pautasso et al 2013 &
Pliūra et al 2011). In this field, Scandinavian countries are leading the way with
breeding trials being developed not only for Ash as a species generally, but also for
trees exhibiting good timber-producing qualities and other breeding programmes
more purely for conservation. Kjær et al (2011), Lobo et al (2014) and Pliūra et al
(2014) have all conducted studies, investigating the potential for breeding highly
tolerant F. excelsior clones and all conclude that this will be feasible. In Denmark, a
joint project between the University of Copenhagen and the Danish Nature Agency
(Naturstyrelsen) has capitalised on an existing clonal breeding programme, which
was set up in the late 1990s and early 2000s. Whilst the programme’s initial purpose was nothing to do with Ash dieback, it allowed researchers a unique opportunity to
study the effects of the disease on different genotypes and then select the most
tolerant of these clones for reproduction. This has afforded the partnership the
confidence to predict that they will be producing highly tolerant F. excelsior seedlings
within 15 years. As an annexation of this project, the Danish Forest Owners
Association (Skovdyrkerne) are identifying Ash trees which not only exhibit high
levels of disease tolerance but also good timber-producing qualities for future
propagation (Fig. 21).
33
A
Joe Alsop, 2014. B
Joe Alsop, 2014.
Figure 21: A: In Denmark, colleagues from the University of Copenhagen and the Danish Forest
Owners Association carrying out fieldwork within an irregular mixed stand, to identify healthy
tolerant trees exhibiting good silvicultural characteristics - this fine, healthy specimen measured
102 dbh. B: With the aid of binoculars and a trained eye, trees are firstly and stringently assessed
from the ground to look for symptoms of Ash dieback - this fine specimen passed the test.
In Sweden, a partnership between the Swedish University of Agricultural Sciences
(SLU), the County Administrative Boards (Länsstyrelserna) and the Swedish Forest
Agency (Skogsstyrelsen) have employed ‘citizen science’ to help. Inviting members of the public to report healthy Ash trees, which they are growing alongside severely
affected ones and seemingly possessing high levels of disease tolerance, they have
identified nearly 400 such trees, which will be used for a selective breeding
programme (Cleary & Stener 2014). The same partnership is also involved with a smaller
programme being set up as part of the EU funded Elmias LIFE project on the island of
Gotland (case study 4). Whilst in comparison to naturally regenerated populations,
clonal breeding programmes will offer a significant reduction in the potential genetic
diversity of F. excelsior, researchers are confident that sufficient genetic variation can
be maintained (Kjær et al 2011, Lobo et al 2014 and Pliūra et al 2014).
34
Case Study 3: Spreewald Biosphere Reserve, Germany.
Visited on the 29.08.2014 and hosted by Eugen Nowak, Principal of the
Spreewald Biosphere Reserve.
Within the UNESCO Spreewald Biosphere Reserve there is approximately 3,500
ha of lowland temperate broadleaf woodland including one of the best
Joe Alsop, 2014
Figure 22: A mixed stand in Lower Spreewald, three years after the 25-30% thinning in 2011,
remaining living high canopy trees are A. glutinosa and the sub-canopy trees are mostly U.
glabra. The dead and dying trees are F. excelsior which have gone from showing some level of
tolerance to H. fraxineus to succumbing within three years.
35
Case Study 3: Continued
examples of wet woodland in Germany. The site was designated as a Biosphere
reserve in 1990 but some areas have held nature protection status, under other
designations, since 1937 and 1960. The reserve has a history of being
permanent forest with some areas of wood-pasture and is managed under a
strict management plan. Within the reserve, the forest areas are either classified
as ‘Core Zones’, which are managed purely for biodiversity with strictly no interventions allowed, or the ‘Buffer Zone’ areas, which are managed as
irregular, high forest where no clear-cutting is permitted but some limited
timber/forestry operations are allowed. The site is designated for a number
different Natura 2000 habitat types, with Pruno-Fraxinetum (91E0) Alluvial
forests and (91F0) Riparian mixed forests being where F. excelsior is a notable
species. Spreewald, situated in the state of Brandenburg, north-east Germany,
receives on average 530mm of rainfall per annum, lies at 51°88' N; 13°81' E and
is between 44-144m above sea level.
Ash dieback was first confirmed as being present in Spreewald in 2006. Prior to
this, there were many A. glutinosa plantations within the buffer zones which
were planned to be diversified and converted to a greater F. excelsior
composition. Part of the reasoning for this was due to the A. glutinosa being
severely stressed by successive years’ flooding with some areas being under
water for up to three months. As a result many stands had been killed by
Phytophthora alni. F. excelsior is a key species within Spreewald, not only as a
natural component of the woodland habitats and their associated ecosystems
but also as one of the few native, canopy-forming, alternatives to A. glutinosa.
In one 15 ha stand in lower Spreewald, aged 110 years old and comprised of
approximately 50% A. glutinosa and 50% F. excelsior, a thinning operation was
carried out in 2011. The intervention removed between 25% and 30% of the
stand and targeted mostly F. excelsior, resulting in approximately 50% of the F.
excelsior being felled. Trees showing Ash dieback symptoms affecting more than
40% of their crown were targeted for removal and specimens which were
already dead and of habitat-interest were left standing. By 2014, many of the
retained F. excelsior, which had been displaying greater levels of disease
tolerance, had died leaving only 1-2% still alive, and of those only one specimen
was observed still in good health (Fig. 22).
36
Case Study 3: Continued
Now Ash is so seriously compromised as a canopy forming component in
Spreewald, alternative species will include A. glutinosa as the primary choice in
the wetter areas and Quercus sp and C. betulus on the relatively drier, yet still
moist, higher ground. Natural regeneration will be the desired method but
planting may be considered as a last resort.
Joe Alsop, 2014
Figure 23: A dead Ash, 35cm dbh, whose bark had once been inhabited by bark beetles. The
bark had subsequently been almost entirely removed by the pecking of feeding woodpeckers.
The trees in the background are A. glutinosa.
37
One very noticeable consequence of the high Ash mortality was the significant
increased bark beetle activity. Trees which had hosted high numbers of beetles
were strikingly obvious, due to being almost entirely stripped of their bark by
feeding woodpeckers (Fig. 23). Similar beetle outbreaks have also been noted by
Skovsgaard et al (2010), Keßler et al (2012) and Kunca et al (2011).
Key findings:
 Trees which can at first appear to have some tolerance to H. fraxineus
can quickly succumb at a later date. This seems especially likely where
further stress has been potentially brought about by a change in site
conditions, e.g. heavy thinning operations causing an increase in the soil
moisture content.
 In comparison to the larger-crowned, more vigorous specimens at the
edges of the stands, much of the forest was typified by dense stands of
relatively small-crowned trees displaying significantly more symptoms of
Ash dieback.
 The increase in standing deadwood habitat, brought about by Ash
dieback, could rapidly diminish due to population surges of other species
capitalizing on this newfound resource, e.g. bark beetles and feeding
woodpeckers destroying flaking bark.
 In woodland habitats, such as the Pruno-Fraxinetum Alluvial forests of
Spreewald, where key tree species are already under threat from disease
(i.e. A. glutinosa from Phytophthora alni), the additional loss of F.
excelsior from Ash dieback will have a serious impact on biodiversity.
38
Case Study 4: Elmias LIFE-Project, Island of Gotland, Sweden.
Visited on the 18.08.2014 and hosted by Karin Wågström of the Swedish Forest
Agency (Skogsstyrelsen), Project Manager of the Elmias LIFE Project.
Ash dieback was first identified on Gotland in 2002 and whilst much of Europe’s Elm population was lost to Dutch Elm Disease (DED) in the 1970’s and 80’s, up until 2005, the island of Gotland was free of the disease. Being 90km from the
Swedish mainland, Gotland is too far for infected Elm bark beetles (Scolytus sp)
to fly, but the likely accidental importation of infected Elm logs is thought to
have brought the disease to the island. The arrival of these two diseases, almost
simultaneously, are now seriously threatening the important and unique
habitats associated with F. excelsior and Ulmus spp on the island. There are
three Natura 2000, Annex 1, habitat types totalling 6774 ha, where both species
Joe Alsop, 2014
Figure 24: High numbers of canopy forming F. excelsior which have succumbed to Ash
Dieback. Ash regeneration was also severely affected.
are key, (6530) Fennoscandian wooded meadows, (9020) Fennoscandian
hemiboreal natural old broad-leaved deciduous forests (with Quercus, Tilia,
Acer, Fraxinus or Ulmus and rich in epiphytes) and (9070) Fennoscandian
wooded pastures. Ash and Elm are by far the principal native broadleaf species
on Gotland, comprising 70-80% of the old growth forests, in addition to
39
Case Study 4: Continued
providing 24% of Sweden’s population of old Ash and 17% of the country’s old
Elms. The Ash and Elm trees and forests on Gotland are particularly important
for their associated lichen communities and many species, such as Lobaria
pulmonaria and Megalaria grossa are nationally scarce species in Sweden. The
island lies at 57◦29’ N, 18◦27’ E and receives 600mm of rainfall per annum. Its
calcareous soils have a high pH and its highest point is 82m above sea level.
Joe Alsop, 2014
Figure 25: An Ash pollard which has succumbed to Ash dieback. The bark was almost entirely
covered in moss and lichen species. Due to the shallow soils and dry conditions, the trees
grow slowly and this Ash is significantly older than its size suggests.
40
Case Study 4: Continued
In 2013, a partnership coordinated by Skogsstyrelsen, secured EU LIFE funding
of €2,125,877 contributing towards a total budget of €4,251,755 (£3,246,581)
for a five year project to tackle the problem. Whilst a large portion of the
funding is directed towards attempting to eradicate DED, an equally important
aim is to ensure the 'favourable' condition status of the Natura 2000 habitats
which are under threat from both diseases. Working towards an EU strategy on
Invasive Alien Species, this element of the project will implement
complementary management prescriptions, working towards making these
habitats more robust, specifically by identifying disease-tolerant Ash genotypes
to establish a clonal breeding programme for future regeneration. As a first
preference, the transplanting of highly tolerant F. excelsior will be trialled but
the project is also working with the Swedish University of Agricultural Sciences
(SLU), to establish a clonal breeding programme. Tree planting will be carried
out to establish the next generation, in addition to varied works to the island’s
large population of Ash pollards, including releasing suppressed trees from
competition and re-pollarding. Allowing Ash dieback to reach its epidemic stage,
Joe Alsop, 2014
Figure 26: Four roadside Ash pollards, all cut at the same time and with differing degrees of
health. The tree on the far left had hardly any symptoms and responded well to being repollarded. The tree which is centre left had actually died with no attempt at regrowth after
pollarding, interestingly this specimen was the smallest of the four - the live growth which is
visible is that of an Acer planted in front of it. The two pollards on the right were both
severely lacking in vigour and struggling to produce sufficient re-growth and will most likely
die.
41
Case Study 4: Continued
before deciding on a course of action for each tree, was felt the most prudent
option and early indications are that carrying out pollarding operations in stages
is less stressful to trees, affording them a greater chance of survival. An
interesting feature of the wooded meadow habitats was the historical
management practice of raking and removing tree leaf litter in the early spring
to promote better grass and herb growth. It would be interesting to see whether
the inadvertent removal of Ash rachis can have an effect on reducing spore
loads in the immediate environment.
Key findings:
 Nationally significant habitats where Ash is a key ecosystem component
and/or important host for other taxa, will require large, ambitious projects
with substantial input, to maintain favourable conditions.
 In sites with veteran and/or pollarded Ash, which have limited resources
relative to the scale of the site, waiting until the disease has reached the
epidemic stage and tolerance levels are truly revealed, will allow the most
efficient targeting of resources.
 Conducting staged re-pollarding could offer Ash trees the best chance to
maintain their vigour and reduce stress, in relation to Ash dieback.
42
Case Study 5: Forêt domaniale d'Auberive, France.
Visited on the 04.09.2014 and hosted by Jean-Jacques Boutteaux, Head Forester
in the Forêt domaniale d'Auberive for the Office National des Forêts.
Situated in the Champagne-Ardenne, the Forêt domaniale d'Auberive has a long
history as a wooded site and in the UK it would be classified as Ancient seminatural woodland. It is mostly managed as mixed, irregular high forest, more
commonly known in Europe as ‘Close-to-Nature Forestry’, where both timber production and biodiversity are key management objectives.
The flatter plateau ground is dominated by F. sylvatica, Quercus spp and
C. betulus but within the slopes and ravines lies Natura 2000 Tilio-acerion (9180)
forest where F. excelsior comprises approximately 20% of the canopy. The other
canopy forming species within the ravine are Tilia spp, A. pseudoplatanus
Joe Alsop, 2014
Figure 27: Whilst the effects of Ash dieback are severe, with such a wide variety of other
canopy forming species present, any loss of canopy cover associated with the disease will
soon be negated and forest conditions maintained.
43
Case Study 5: Continued
and F. sylvatica. The forest covers a large area but this case study concentrates
only on one of the ravine sites, at 47◦45’ N, 5◦11’ E, which receives 900mm of
rain per annum and is on calcareous soils with high pH.
Joe Alsop, 2014
Figure 28: Within the ravine forest, this 25 year old stand, comprised mainly of A. pseudoplatanus with some F. excelsior, had received a number of thinning interventions resulting in
good levels of light reaching the woodland floor - something not usually associated with an
A. pseudoplatanus comprised canopy.
Ash dieback was first identified in 2009, although it is suspected that it may have
arrived before that date. By 2011, its effects were widespread and in 2014 it was
highly apparent that the disease was well into its epidemic stage. All trees were
showing symptoms associated with H. fraxineus and non-forest trees, growing in
fields, boundaries and along roadsides were considered to be more susceptible
than the Ash growing within the forest - this was certainly very evident. Since
2009, nearly 15% of the Ash population in the forest area had succumbed to the
disease and a further 25% were so severely affected it was expected that they
44
Case Study 5: Continued
would die within the next year. In addition, one of the other serious
consequences of Ash dieback was that whilst Ash was still producing seedlings
and saplings, none were surviving beyond a few years of growth. Within the
forest in areas where Ash regeneration used to dominate, its loss was already
becoming apparent allowing other species such as A. pseudoplatanus, A.
platanoides, F. sylvatica and T. torminalis to take over. As part of forest practice,
areas of natural regeneration are thinned as they approach thicket stage and
attempts had been made to promote Ash to elevate the effects of the disease
but were unsuccessful.
Key findings:
 Given the right set of conditions, Ash dieback can develop and spread
alarmingly fast.
 The effects of the disease can vary greatly from country to country.
 In comparison to single-species even-aged stands and forests, mixed
woodlands managed by ‘close-to-nature forestry’ principles are far better placed to adapt to and mitigate against climate change and/or the arrival
of new invasive pests and diseases.
 In the face of climate change and new pest and disease threats, having a
sound knowledge of the silvics of tree species, in addition to practicing
good site based silviculture should be considered essential for future
woodland management.

45
Conclusion
Since it was first identified within the UK, the spread and severity of Ash dieback has
been less than many anticipated and some may believe that Ash dieback is not as
serious as first thought. This delay is in no doubt partly due to the various
environmental factors which can influence Ash dieback’s development (Dal Masso &
Montecchio 2014) but also the disease is still in its lag phase and yet to reach the
exponential stage (Gross et al 2014). It was thought initially, in comparison to the East,
that trees in the West of Sweden had greater levels of disease tolerance but
experience proved that this was merely a result of its initially slow spread across the
country (Bengtsson 2013). When the epidemic does reach the exponential stage,
experience from Europe indicates its spread and development will become greatly
accelerated (Gross et al 2014). Whilst in comparison to European F. excelsior
populations currently being affected by Ash dieback, Ash in the UK does have a
slightly different genetic lineage (Heuertz 2004), but as there appears to be no
significant difference in disease susceptibility amongst all other European lineages,
this gives little reason to believe that Ash dieback will not have a similar impact in the
UK.
In contrast to how Ash dieback has developed in other countries, where tree planting
is not widespread, it is clear that throughout the UK the natural spread of the disease
has been further exacerbated by the planting of infected trees. The most recent
mapping of Ash dieback within the UK shows a large area of infection, recently
identified in Lancashire (Forestry Commission 2015), well away from the disease’s
suspected wind-borne arrival in the East (Fig. 29). This would suggest that the most
recent modelling of how quickly the disease will spread (University of Cambridge 2014),
which assumes infection from planted sites as insignificant, may be considered to be
a little too conservative. With this and its highly likely severity in mind, tree and
woodland managers should not underestimate Ash dieback.
In the short term, within mixed woodlands, the loss of Ash from the canopy will have
negligible effect as dead trees should be readily replaced by the expanding crowns of
their neighbours. However, in more Ash dominated stands and woodlands, the loss
of canopy cover is likely to cause a relatively rapid degradation of the ‘forest
environment’. This will be especially prevalent and the effects prolonged, within woodlands comprised mostly of Ash, which are single storey, lack natural
regeneration potential or have an impoverished, poorly developed shrub layer
46
A
Forestry Commission, 2015.
B
Engesser & Meier, 2014.
Figure 29: A comparison of how Ash dieback has developed over a three year period since it was
first identified in A: The United Kingdom, where infected planting stock has clearly spread the
disease further than it would have naturally done so, solely by wind dispersal; B: Switzerland,
where tree planting within forests is almost non-existent as natural regeneration is relied upon,
consequently the disease has developed naturally - spreading like a wave south through the
country.
and/or sub-canopy. The temporary collapse of ecosystems reliant on Ash (Kjær et al
2011) will in turn affect many Ash associated species, especially those which are
obligate (Mitchell et al 2014a) or epiphytic (Jönsson & Thor 2012) on the species. Longer
term, the fact that the health of trees, even those which at first appear to be suitably
disease tolerant, is now shown to be steadily deteriorating over time (Enderle et al
2014, Lobo et al 2014, Pliūra et al 2014 & Pliūra et al 2011) has serious implications for Ash
associated species and ecosystems. This is further compounded by the fact that in
many areas, Ash regeneration, although initially plentiful, does not survive. In
addition, as the epidemic is still developing and shows a lack of clear trends in its
47
seasonal variation and severity, making future predictions of how the disease will
develop almost impossible (Stener 2012). As studies have shown that the genetic
diversity of H. fraxineus throughout its native range in Asia is considerably higher
than that of the European population (Gross et al 2014 & Zhao et al 2012), this poses the
potential scenario that if any additional genetic strains were introduced they could
prove even more deadly.
The long term effects of Ash dieback on ecosystems will be felt especially within
woodland habitats which have previously suffered the loss of other key canopyforming tree species and where Ash is now dominant (Pautasso et al 2013 & Peterken
2013). The ravine woodlands of the Derbyshire Dales are a good case in point: their
tree species composition is already seriously impoverished in many areas, with
intensive agricultural and industrial activity being primary factors in the removal of
Tilia sp from many stands and the widespread depletion of Ulmus sp due to disease
(Merton 1970, Peterken 1996 & Piggot 1969). An additional cause for concern in such seminatural woodlands will be which tree species will begin to replace Ash and in many
cases A. pseudoplatanus may be the strongest contender. Where it is present, the
break in canopy cover, in conjunction with the expected reduction of Ash’s natural regeneration potential, will surely give A. pseudoplatanus the competitive advantage
to dominate (Binggeli 1993, Hein et al 2009, Petritan, Luepke & Petritan 2007 & Stiven 2007).
Whilst A. pseudoplatanus can support a good number of Ash associated species, it
does not possess the same ecological characteristics as Ash and cannot provide equal
ecosystem functions (Mitchell et al 2014a & Mitchell et al 2014b). Also, in comparison to
woodlands comprised of lighter-canopied tree species such as Ash, A.
pseudoplatanus casts a much denser shade and where it takes over, it alters the light
regime and has a significant reduction on the species richness of the ground flora
(Binggeli 1993). Within such situations, careful consideration will have to be given to
the long-term prospects for biodiversity and considering climate change and the
increased threat from new pests and diseases, it wouldn’t be wise to allow another single tree species to become ascendant.
Within even-aged and single-species woodlands, where timber production is also a
concern, the arrival of an invasive disease, such as Ash dieback, can devastate and
cause total stand collapse resulting in a serious loss of value. It was very apparent
throughout the trip, that in comparison the practice of close-to-nature forestry
management is at a clear advantage (case study 5). Close-to-nature forestry not only
facilitates resilience through having a wealth of other replacement tree species to
choose from but also through having these species growing in a full range of age
48
classes throughout the woodland. Therefore, in the event that one species becomes
threatened and begins to die, the site manager has adequate options for its
replacement, thus not only maintaining woodland conditions and ecosystem integrity
but also minimising the potential loss of revenue.
For Ash dominated woodlands in the UK now threatened by Ash dieback, the
diversity resistance hypothesis, which maintains that the more diverse
an ecosystem, the more resilient it is to invasive pests and diseases (Kennedy et al
2002), has never been more poignant. As possibly the most unique of the UK’s canopy forming native broadleaved trees (Mitchell et al 2014a) and one which is already
bearing an increased ecological burden due to the loss of Ulmus sp, F. excelsior must
not be forsaken. Yet in habitats where it is a key species, adapting current
management practices and adopting new ones is the best option to counter the loss
of forest conditions and help preserve ecosystem integrity (Ellison et al 2005 & Loo 2009).
Within these sites, any endeavours towards mitigating against the likely loss of Ash
will require the input of substantial time and monetary resources. Managers should
plan now how to not only ensure habitat continuity but also make ecosystems more
robust, species diverse and resilient. This would also be beneficial for predicted
climate change (Brang et al 2014) or the arrival of any other new pests and diseases
(Ennos 2015), such as the looming spectre of the Emerald Ash borer, Agrilus
planipennis (Straw et al 2013).
49
Recommendations
Management of Stands Prior to Infection_______________________
Whilst canopy control is still held, efforts should be channelled towards diversifying
stands and enabling them to become as resilient as possible. This will minimise the
likely degradation of woodland conditions and ecosystem dynamics which will arise
from Ash dieback, yet still allow for the potential of some Ash trees having good
levels of disease tolerance.
 Where practicable, avoid felling prime and vigorous Ash and those which have
an early phonological sequence, as these trees offer the greatest chance of
possessing disease tolerance.
 In stands with much to lose (such as those where timber production is an
objective, those which are Ash dominated with no or few other tree species
present as replacements, or groups of Ash which are at the critical stage of
their development, i.e. where they switch from being shade tolerant to more
light demanding and are strongly competing,) could be thinned, promoting the
prime and vigorous specimens.
 In areas where Ash comprises large proportions of the species composition, yet
there are other desirable tree species present or close by, release and promote
these alternative species and facilitate conditions to suit their natural
regeneration.
 In Ash-dominated stands with a suitable understorey species present, such as
Corylus avellana, ensure that these plants are optimised to have the potential
to assume the canopy and maintain woodland conditions. Coppicing, layering
and stooling could all be trialled in addition to ensuring they have adequate
light to regenerate.
 In truly Ash-dominated stands with no or few options for alternative species to
replace Ash or maintain woodland conditions, the introduction of suitable
alternative species will be required by under-planting.
 In Ash-dominated stands with little Ash regeneration, conditions could be
manipulated to encourage its natural regeneration, potentially allowing
tolerant trees to establish.
 Eschew the pre-emptive clearance of Ash to avoid loss of timber value as
potentially tolerant trees may be lost.
50
Management of Infected Stands______________________________
Once areas become infected it will take a number of years for truly tolerant trees to
be revealed, so early presumptions and associated decisions should be avoided. The
speed with which Ash will diminish from the canopy will be dependent on a number
of different factors. Efforts should be directed towards maintaining woodland
conditions and ensuring habitat continuity whilst still allowing Ash every chance to
survive and naturally regenerate.
 Avoid heavy thinning or clear-felling operations.
 Where tolerant trees are revealed, ensure (where practicable) conditions are
maintained as stably as possible and that they are free from additional stress
factors, such as being suppressed by neighbours.
 Ensure adequate numbers of seed bearing female Ash trees are retained
throughout woodlands to enable good natural regeneration potential.
 Where tolerant seed trees are present, manipulate woodland conditions to
become optimal for seed germination, survival and establishment.
 In the event of Ash regeneration surviving, ensure it is suitably managed to
promote tolerant specimens and alleviate stress and competition.
 Within heavily affected stands, even retaining trees which have lost
commercial value and will likely die could be important for maintaining
woodland conditions and aiding future stand management.
Additional Points___________________________________________
 The selection of alternative tree species should be based upon the historical
natural composition of the woodland, sound silvicultural understanding of the
site’s conditions and associated tree silvics. Additionally, consider the species’
capability to ensure habitat continuity for Ash-associated species and
ecosystems and their suitability for the future in relation to pest and disease
threats and climate change.
 For Ash coppice and pollards, where practicable, waiting until they are under
infection pressure and their disease tolerance has been revealed may be the
best method to avoid futile works. In addition, staging the works and
monitoring how individual trees respond would also seem sensible.
 Due to the likely fragmentation of highly tolerant Ash specimens, efforts will be
required at a national scale to ensure that sufficient genetic diversity within
the species is maintained.
51
 Ulmus sp should be reconsidered: In Spain a European Commission LIFE funded
project is working on the back of a 27 year old Elm Breeding Programme
(RESGEN 78, ‘Conservation of Genetic Resources of European Elms) which has
produced seven DED resistant U. minor clones and is using them to restore
previously decimated Natura 2000 habitats.
52
Acknowledgements
A great deal of thanks is offered to all the staff of the Winston Churchill Memorial
Trust (WCMT) for recognising the potential of the project, awarding me the
Fellowship grant and for all their help throughout. I would also like to thank the
following staff of Natural England for their assistance, namely; Christine Reid and
Kevin Bull for providing me with excellent references and their valued support
throughout, Chris Gardiner for his help and advice during the application process,
Ben Le Bas, Dan Abrahams and Emma Goldberg for their help and suggestions and
Mark Wood and Shaun Taylor for taking up the slack in my absence. I’m also grateful to the following people for their help and suggestions in making contacts and
identifying suitable locations to visit; Andy Poore, George Peterken, Keith Kirby,
Louise Roum and a very special thanks to Vikki Bengtsson. I’m particularly grateful to the following people who I met on my trip and went out of their way to offer
additional help and/or contacts, or much welcomed, kind hearted and generous
hospitality; Anne Wevell, Berthold Metzler, Danièle Murat, Erik Dahl Kjær, JeanJacques Boutteaux, Jörg Brunet, Karin Wågström, Ludovic Rouyer, Rimvydas Vasaitis
and Valentin Queloz. A special thank you also to the following people who gave me
their valuable time and knowledge during the trip; Audrius Menkis, Catherine Huerta,
Christoph Scheidegger, Ditte Christina Olrik, Eugen Nowak, Gunnar Isacsson, Håkan
Elmqvist, Hannes Napp, Jan Stenlid, Jens Peter Skovsgaard, John Nordqvist, Karsten
Raae, Lars Nørgaard Hansen, Lea Vig McKinney, Matthias Schlund, Michelle Cleary,
Roland Engesser, Simone Prospero and to all those other people who I haven’t mentioned - I apologise for my atrocious ability in remembering people’s names! I’m additionally grateful to all the people, whom are too numerous to mention
individually, who replied to my emails with help, advice and suggestions of people
and organisations to contact. Thank you to Emma Alsop for proof reading and thank
you also to my Mum, Margaret Alsop - Churchill Fellow 1977, who through
advocating the WCMT gave me the inspiration to apply.
53
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63
Itinerary
Monday 11th August:
Tuesday 12th August:
Wednesday 13th August:
Thursday 14th August:
Friday 15th August:
Saturday 16th August:
Sunday 17th August:
Monday 18th August:
Tuesday19th August:
Wednesday20th August:
Thursday 21st August:
Friday 22nd August:
Saturday 23rd August:
Sunday 24th August:
Drive from Derbyshire to Dover. Ferry crossing to Dunkirk,
France.
Driving to Denmark via Belgium, Holland and Germany.
Meeting with Lars Nørgaard Hansen, of the University of
Copenhagen, at ‘Als Nørreskov’ on the Island Als in Southern Jutland to assess disease levels.
Meeting with Ditte Christina Olrik of the Danish Nature
Agency (Naturstyrelsen) in Græsted, Denmark to learn
about Ash dieback and associated management.
Meeting with Erik Dahl Kjær and Lea Vig McKinney, of the
University of Copenhagen, in Hørsholm to discuss their
breeding programme for resistant Ash trees.
Drive through Sweden. Ferry crossing to the island of
Gotland, Sweden.
Rest day on Gotland.
Meeting with Karin Wågström of the Swedish Forestry
Agency (Skogsstyrelsen) and Håkan Elmqvist (Lepidoptera
specialist) to visit various sites on Gotland and learn about
the Life project ‘Elmias’ and their work with Ash dieback and DED.
Meeting with Audrius Menkis, of the Swedish University of
Agricultural Sciences (SLU), to visit Ash dieback sites and
work with DED.
Ferry crossing to Swedish mainland and drive to Uppsala.
Meeting with staff at the Swedish University of Agricultural
Sciences (SLU) inc Rimvydas Vasaitis, Audrius Menkis,
Michelle Cleary and Jan Stenlid, to discuss Ash dieback.
Drive to Malmöhus County, southern Sweden.
Meeting with Jörg Brunet, of the Swedish University of
Agricultural Sciences (SLU), at Dalby Forest National Park.
Driving to Hässleholm
Meeting with Gunnar Isacsson, of the Swedish Forestry
Agency (Skogsstyrelsen), to learn about Ash dieback and
associated forest management.
Rest day in Sweden.
Driving to Denmark.
64
Monday 25th August:
Tuesday26th August:
Wednesday 27th August:
Thursday 28th August:
Friday 29th August:
Saturday 30th August:
Sunday 31st August:
Monday 1st September:
Tuesday 2nd September:
Wednesday 3rd September:
Thursday 4th September:
Friday 5th September:
Saturday 6th September:
Sunday 7th September:
Monday 8th September:
Tuesday 9th September:
AM; Meeting in Copenhagen with Karsten Raae, of
Skovdyrkerne and Dr. Lea Vig McKinney, of the University of
Copenhagen, to discuss their breeding programme for
resistant Ash trees.
PM; Meeting with Jens Peter Skovsgaard, of the Swedish
University of Agricultural Sciences (SLU), to discuss forest
management and Ash dieback.
Driving and ferry crossing to Germany.
Driving to Baden-Württemberg, Southern Germany.
Meeting with Berthold Metzler, of the FVA research
Institute of Forest Management, in Freiburg to discuss Ash
dieback and forest management.
Meeting with Berthold Metzler and Anne Wevell, of the FVA
research Institute of Forest Management, to visit Ravine
Forests and discuss Ash dieback.
Driving to Brandenburg, Northern Germany.
Meeting with Eugen Nowak, of the Spreewald Biosfere
Reserve, to discuss Ash dieback and forest management.
Rest day.
Driving to Bavaria, Germany.
Meeting with Matthias Schlund (District Forester) and
Hannes Napp, of the Biosphärenreservat Rhön, to discuss
Forest management and Ash dieback.
Rest day.
Driving to France.
Meeting with Jean-Jacques Boutteaux, of the Office national
des forêts, to discuss Ash dieback, Ravine forests & CCF.
Driving to Luxembourg.
Meeting with Anne Wevell and Danièle Murat, of the
Service des forêts, to discuss Ravine forest management.
Drive to France to visit to Reserve Naturelle Combe de
Lavaux Jean Roland.
Driving to Switzerland
Meeting with Valentin Queloz, of the Institute for
Integrative Biology, to discuss Ash dieback and woodland
management.
Meeting with Valentin Queloz to visit the Swiss National
Arboretum.
65
Wednesday 10th September:
Thursday 11th September:
Friday 12th September:
Saturday 13th September:
Sunday 14th September:
Monday 15th September:
Tuesday 16th September:
Wednesday 17th September:
Thursday 18th September:
Friday 19th September:
Saturday 20th September:
Sunday 21st September:
Meeting with Christoph Scheidegger, Roland Engesser and
Simone Prospero at the Swiss Federal Institute for Forest
Snow and Landscape Research (WSL), to discuss Ash
dieback.
Rest day in the Swiss preAlps
Driving North through Germany.
Driving to Kiel, North Germany.
Ferry to Lithuania.
Rest day
COST Ash dieback conference.
COST Ash dieback conference.
COST Ash dieback conference.
Ferry to Germany.
Driving to France.
Ferry crossing from Dunkirk to Dover then Driving home.
66
“Going to the woods is going home.” - John Muir.
Prästeboda naturreservat: Sweden, 2014.
67