ADDENDUM - January 2013
There are recurring themes that I cannot seem to escape, and which drain away energy that should be used to explore a better prospect for wild nature in Britain. Chief amongst these themes is the conservation industry’s unholy trinity of Higher Level Stewardship, fencing and livestock grazing, and which I seem destined always to return to, and will do so shortly, to document more of the scandal that it is. But before that, I have to say goodbye to ash trees, and grieve over the upcoming loss of a familiar feature of the woodlands that I walk.
I don’t profess to have an early grasp on everything that goes on in the natural world, but I was shocked to read about ash dieback in an Observer article from early October (1). It was the first time that I had heard of the existence of the fungal disease that has damaged many ash trees in continental Europe, and particularly in Denmark, Germany, Poland, Norway, Sweden and Austria, and which had begun to turn up in Britain. I didn’t need to check any further to get that foreboding I have had only once before, at a lunchtime seminar on HIV-AIDS in 1983 while I was working in a teaching hospital in America. A doom-laden prospect has weighed heavily on both occasions.
A devastating tree-bashing fungal infection
During my lifetime, we have lived with a devastating tree-bashing fungal infection in Dutch Elm Disease. It first appeared in north-west Europe around 1910, dieing down by the 1940s after causing losses of 10—40% of elms in different European countries (2,3). It gets its name not for the origin of the disease, but because of significant research in the Netherlands on that first outbreak. A second and far more destructive outbreak of the disease started in the late 1960s when a new strain of the fungus was imported into Britain on infested elm logs from Canada. The disease raged through the English elm population (Ulmus procera) a tree not native but probably introduced with the Romans, and which was the predominant elm in Central and southern Britain. Most of the mature English elms were lost within a decade, some 25 million trees out of a population estimate of 30 million, but a few large English elm remain dotted around the countryside, and which have probably avoided infection through lack of exposure to the bark beetles that are the vector that spreads the disease.
After infection the fungus in a yeast-like stage is spread through the sap of the tree, releasing toxins, and puncturing the xylem with its mycelium. What kills the trunk of the tree is its own reaction to the fungal infection, which is a blocking of its water conduction system through a plugging up of the xylem with gummy extensions of the xylem wall, and which thus results in wilting and death of the foliage. English elms sucker, and the natural root grafts they create under ground with neighbouring trees directly spreads the fungus. They will never grow back from these suckers to the towering trees they once were because of cycles of growth followed by re-infection and above ground death.
I can’t say that I remember the loss of these English elms in the early 70s, as they weren’t a feature of where I grew up on the south coast, or wherever I was in the couple of decades afterwards. It was when I moved to live in the north that the effects of the disease became apparent – it seemingly moved northward at the same time as did I. The evidence is in the dead and decaying stumps of Wych elm (Ulmus glabra) left after the trunk of the tree had died and plunged to the ground. However, the tree is not dead as the roots are not killed. Thus the tree reacts as though it has been coppiced, sending up growths from adventitious buds that produce new trunks. They in turn may become infected, but the elm bark has to be of a certain thickness before the bark beetle can invade and breed successfully. Thus it is some years before infection and death can strike again.
The Wych elm is the elm of the north, and likely the only native elm. It is a favourite tree. I look forward each spring to its very small, rich ruby red flowers on short stems, in clusters of 10-20, that appear before the leaves. Very characteristic groups of keys, a winged fruit, develop after wind pollination, having a single seed at the centre of each key. The leaves are the largest of any of our native trees, and are oddly shaped at their base as they don’t meet the stalk at the same point. The leaves have jagged, toothed edges that end at a point, although the leaves on younger stems tend to have a spikey lobe either side of the point, making them look like ears. We don’t have much colour in our autumn leaves, dog wood, spindle and guelder rose aside, but Wych elm have a strong yellow to their leaves before they fall, and which brightens up a woodland.
I see many distinctive uninfected young Wych elm that have seeded in to ancient woodland around me, often seeming to create a foliate sub-canopy over water courses, as well as Wych elm of significant girth (about 20cm across) that have surprisingly yet to succumb to infection. That Wych elm don’t sucker like English elm is an advantage against the disease, since individual trees will not therefore link together through root grafts, spreading the disease between them. Wych elm are also less palatable to the bark beetle than English elm, and even when they do start to feed on bark, there is a fungus, Phomopsis, attracted to elm that are under stress, and which releases chemicals that deter the bark beetle from boring and feeding. On this basis, the future for Wych elm in our northern woodlands would seem only to be limited if the re-infection of regenerating trunks occurred before they had matured enough to produce viable seed, or if seeded-in trees did not mature enough to also produce seed before they were infected. The evidence around me is that this doesn’t appear to be the case.
The outlook for ash
The outlook for ash doesn’t seem so good. Ash dieback is caused by a fungus, Chalara fraxinea, identified in the 1990s in mainland Europe. Its first confirmed sighting in Britain was in February this year in a consignment of infected trees sent from the Netherlands to a nursery in Buckinghamshire (1). In June 2012 it was found in ash trees planted at a car park in Leicestershire that had been supplied by a nursery in Lincolnshire. Then in July there were confirmed cases in the nursery trade in West and South Yorkshire and Surrey, and by September it had been reported in a nursery in Cambridgeshire. At the time of that article in October, it had also been found out in the wider countryside, in two mature woodland areas in East Anglia: one in Suffolk at Pound Farm owned by the Woodland Trust (4) and the other at the Norfolk Wildlife Trust's Lower Wood reserve at Ashwellthorpe (5). DEFRA then confirmed that 100,000 newly planted saplings, and saplings trees at nurseries, all imported, had been destroyed in an effort to prevent the disease spreading (5). Over a few days in early November, hundreds of staff from government agencies as well as volunteers went out looking for signs of the disease, and confirmed infections occurring in established woodland in Kent and Essex, bringing the number to 52 locations, which then almost immediately jumped to 82 (6,7). Another two days on, and DEFRA confirmed more infections out in the countryside in six new counties: Berkshire, Bedfordshire, Lincolnshire, Northumberland, Sussex and Yorkshire, giving a total of 115 sites in 11 counties, including some in Wales and Scotland, the map from the Forestry Commission showing sites where ash had been planted, and sites where it had arisen in existing ash trees (8). The number of sites doubled again to 291 in the first week of December, 136 of those sites linked to imported plants (9). It was 323 by the 19 December with 17 at nursery sites, 143 at recently planted sites, and 163 in the wider environment of established woodland (10).
It seems the
more you looked, the more infections could be found. This escalation in
confirmed sites was not a natural progression of the disease: it must have
already been here, and for some years. The blame game has reverberated
ever since the news broke two months ago, with Government only applying an
import ban on ash trees at the end of October (11) even though it was
revealed that the Horticultural Trades Association had informed DEFRA
three years ago about the likelihood of the disease arriving through
imported trees. Tim Briercliffe, its director of business development,
questioned why we have been importing ash trees, when they seem pretty
good at seeding just about everywhere. It will not have helped that the
Woodland Trust may have been buying trees from nurseries that sent ash
seed to the Netherlands to be grown as nursery stock, and then had the
trees imported back in (13). Peter Marren, a nature author, was
particularly scathing of the swerving sidestep of this issue that the
Woodland Trust has attempted (14):
It is likely that their planting schemes have done much to introduce and spread the disease, since the recently planted woodland on a friends farm has been confirmed to have ash dieback, the trees having come from the Woodland Trust.
Government also ignored a recommendation from the Forestry Commission in July 2011 that ash trees should only be imported from areas free of the fungal disease (15). It certainly was the responsibility of the Forestry Commission to propose this, as it is tasked by the Plant Health Act 1967 to protect forest trees and timber from attack by pests and diseases through making orders for preventing the introduction of a pest or disease into the country, and preventing the spread of a pest or disease through the removal, treatment or destruction of any seed or plant (16). Unfortunately, in fulfilling its statutory role in controlling pests and diseases under the Plant Health Act, the Forestry Act 1967 says the powers of the Forestry Commission to make those orders must "comply with such directions as may be given to them by.... Ministers" (17). The evidence of incompetence continued when MPs were recently told that action against the ash dieback fungus was delayed by a lack of qualified plant pathologists (15). I'm beginning to think that the uncertainty over the future of the Forestry Commission since the debacle of the Governments attempt to sell off the Public Forest Estate in England, and the forced shedding of so many employees from the Forestry Commission, has clipped its wings in fulfilling its statutory role in controlling timber pests and diseases.
The natural spread of the ash dieback
Moving past the row over spread of the disease by importation, the natural spread of the ash dieback fungus is by wind-blown spores or rain splashes onto leaves during June to October, but mainly in July (18). There does not seem to be a vector for the disease (19). The infection is seen as a progression of necrosis - the dieback of cells - extending along the veins and midrib of the leaf, drying it up in the process and killing it (20). Leaf symptoms can be detected within two months of infection. The necrosis continues into the leaf stalk and on into stems and branches, producing cankers and bark discoloration as well as discoloration of internal wood, the stem and branch lesions appearing in the growing season following infection. The disease in young trees results in dead side shoots and tops. Older trees show withered tops from marked dieback of shoots, twigs and branches in the crown, and often prolific growth of new shoots lower down (epicormic growth) that are a symptom of the tree vainly trying to recover from the injury being sustained. Re-infection occurs from spore production from fruiting bodies on infected fallen leaves and shoot material over the summer of the growing season after infection. Seed production can also spread the disease, since the fungus is present in the winged fruit shed from infected trees.
Ash trees do not seem to recover from infection, but the impact does depend on tree age (20). Dieback of ash is particularly destructive of young ash plants, killing them within one growing season of symptoms becoming visible, which suggests that the die back travels down as far as the roots, killing them also. Other ash trees up to 10 years of age are likely to die within 2-10 years. Older trees can survive initial attacks, but continue to degenerate over several seasons of infection. If there are other secondary pathogenic/opportunistic organisms around, such as honey fungus, then a tree under 40 years old will die within in 3-5 years. For mature trees older than 40 years, there is not enough evidence yet from other countries to be sure how long if at all the progression to death will take.
The implications of the spread of ash dieback across Europe were considered in a recently published review, which concluded that the death of vast numbers of common ash trees is likely to have major ecological consequences for European biodiversity and forest ecosystems (21). In particular the authors drew attention to the keystone role of ash in floodplain forest ecosystems, which can be found in Belgium, Germany, France and the Netherlands, as well as Austria, Bulgaria, Czech Republic, Italy, Poland, Romania, Slovenia and Sweden (22). These riparian forests have already been impoverished in recent years by the loss of many elm trees due to Dutch Elm Disease, and alder and oak trees due to Phytophthora water molds (21). The loss of a high proportion of ash trees is likely to have a cascade of effects on the ecology of not only these riparian woodlands, but also the increasing number of ash in recent years in oak woodland across Europe.
The impact in Britain has not yet received much in the way of any rational analysis. Ash is the third most common broadleaf native tree species in Britain after oak and birch, with a population of 80 million (7). The ecological and physiological flexibility of ash is demonstrated by it being somewhere between a pioneer species and a permanent forest component, its saplings having shade tolerance, but it is light demanding as a mature tree. It avoids anything more than moderate acidity (>ph 4.5). For organisms that specifically depend on ash, the loss of ash trees from entire landscapes would mean the loss of their habitat, and thus potentially their extinction. Many insects feed on ash, the Biological Records Centre listing 111 species associated with ash, of which 27 have ash as the sole food plant, and 12 where it is the main food plant (23). Amongst these are mites, gall midges, capsid bugs, aphids, moths, plant lice, a sawfly, and a thrip. Ash hosts many hundreds of fungal species on its living, dieing and dead wood, a few being specific to ash, such as the wood-decaying fungus Peniophora limitata, the canker forming fungus Botryosphaeria stevensii, and the woodwart fungus Hypoxylon intermedium (24).The light dappled shade beneath the canopy of the ash is ideal for many of the lichens that grow on tree bark and wood (25). The British Lichen Society shows there are 536 lichens associated with ash, just over a quarter of the British lichen flora, but nationally there are few specialists that are wholly or largely confined to ash. The issue here is in the loss of older lichen rich ash trees that constitute a significant proportion of lichen habitat.
Ash as the predominant tree species
will not be an issue for floodplain woodland here, as the great floodplain
forests of England along the Trent, Ouse, Severn, Avon and Thames Rivers
were long ago cleared to make way for agriculture on the rich alluvial
deposits (22,26). Where ash dieback will have its greatest impact is in
the woodland where it is the predominant tree species. This was quickly
pointed out by Stephen Barlow in the discussions on breaking news of the
disease (27). Stephen is an ecologist and wildlife photographer living on
the other side of the Pennines from me, but whose experience of ash
woodland in the north is much nearer my own (28). The Centre for Ecology
and Hydrology (CEH) prepared a summary of data on ash tree distribution
that Stephen quite rightly described as extremely misleading (29). He
explained that the map showed low densities of ash trees in some of the
areas where they are one of the most important tree species (30):
describes itself as a “Centre of Excellence for integrated research in
terrestrial and freshwater ecosystems”. However, it was remarkably naïve
of the CEH to put forward their smeary distribution map for ash as making
any useful contribution (31,32) when ash occurs widely in much woodland,
but is the predominant tree species in only 129,000ha of out of a total of
1,487,000ha of broadleaf woodland in Britain (7, 33) and with 105,000ha of
that ash woodland in England (10.6% of the total) (34). Stephen again
added some clarity when he explained that the National Vegetation
Classification, a system
based on the floristic-phytosocial association of trees, flowers, mosses
and lichens, identifies two woodland types in which ash is the
dominant tree, and given the identifiers W8 and W9 (35). He pointed to a
very useful graphic in a Forestry Commission note that provides a flow
diagram to determine the NVC type for existing woodlands, depending on
their composition and the soil moisture and ph, and their geographical location (36). This
shows that W8 is a lowland woodland type characteristically found in the
warm SE of England on alkaline clay soils, whereas W9 occurs in the
uplands of the cooler north of England that have higher rainfall but
freely draining, alkaline soils. Stephen then pointed to the distribution
maps for these two woodland types in the NVC Field Guide to woodland and
which shows that W9 woodland tends to be confined to the more upland
limestone areas in the north, and is pretty much absent in the south east
(37). As Stephen said (35):
(W8) near Grassington in the Yorkshire Dales has many mature ash trees in what
was once an ash-hazel wood pasture. It’s an ancient woodland on limestone
pavement that has been free of sheep grazing for some time (38). It also
has little of the alien disturbance from non-native trees, nor human
management now from a past history of hazel coppice, so that I think of
Bastow as being endowed with a wonderful atmosphere of wildness. I can
imagine a restoration of lynx to the wild there. I went to Bastow Wood
shortly after the news about ash dieback broke because I wanted to say
goodbye before the disease sets in. I will have to leave it to next year
to say goodbye to Scoska Wood National Nature Reserve (NNR) (W9), Ling Gill NNR
and Colt Park Wood (W9) in Ingleborough NNR, those inaccessible and very wild
ash woods on limestone, that have rowan, Wych elm and bird cherry, and
with understories luxuriant with lichens, ferns and mosses (39). The
description of W9 ash wood in the NVC field guide truly captures these
The non-intervention character of all four of those ash woodlands on limestone may give them respite from the pace of ash dieback. A study on coextinction of lichens with ash trees on Gotland Island in the Baltic Sea off Sweden found that traditionally managed open wooded meadows had the highest incidence of ash dieback disease compared with semi-open grazed sites, and with unmanaged closed forests having the lowest incidence (40). The developing ash woodland on Scar Close is also non-intervention since grazing was fenced out from this limestone pavement in 1974 (39). I was planning a trip there with a landscape artist to show her the remarkable transformation, when news of ash dieback broke. Bad weather cancelled the visit, but it got me to thinking what would be the consequences for Scar Close when the ash dieback fungus finally reached it.
The distribution systems of wild nature
The ecological restoration that has taken place at Scar Close has been aided only by the distribution systems of wild nature, the reclaiming of species mediated through the natural force of wind, and the assistance of birds and mammals, the seeds in their droppings or on their fur. That this is a developing, functioning ecosystem is readily apparent through the contrast with the depauperate state of the grazed pavements surrounding it, and the obvious difference in vitality. The regenerating woodland of ash is just past the shrub stage and into low canopy. These trees may never grow fully due to the thinness of the returning soil and exposure to the wind of the upland climate, but the shadier areas beneath their canopies have a lushness of ground layer vegetation, and one can only speculate on what invertebrate life exists in the accumulating decomposition. Butterflies revel in this reforming woodland and there is the sound of birds, missing from the grazed areas.
Amongst the major differences on this pavement is that the wildflowers are growing on it’s surface rather than in the clints and grykes, the deep joints in the limestone. Scar Close has three times the floristic diversity of the nearby grazed pavement of Southerscales (41). This has happened because of the build up of humus and soil-making resulting initially from ash leaf fall, but which then proceeds on the herbaceous cycle of plants combined with the leaf fall. The mix of plants at present cuts across many of the common plant strategies, and so it is neither all shade species (or obligate shade) or all open ground species. It is a botanical garden that could act now as the source of species for the ecological restoration of all the surrounding pavements, but only if grazing is also removed from those pavements as well.
It is difficult to say what would be the immediate changes in vegetation on this pavement when ash dieback hits it, considering that there is already some vegetative foothold on the surface in the existing soil and humus. Would there be a process of loss of this surface soil with a loss of tree cover? In the absence of extractive pressures (the sheep) – which of course is why all this transformation started happening anyway – then maybe not in the short to medium term, but the fear is that the soil will be eroded away by rainfall, as happened when the soil was originally lost from these pavements when they were first deforested by early farmers.
The dead ash trees will of course provide their own increase in habitat for saproxylic species that live on decaying wood, and those that use tree holes. The lower canopy cover will mean a loss of micro-climate. It will also lead to a reduction in butterflies and birds. Sycamore will become the main tree, if the seed rain continues from a nearby grazed pavement. My observation is that ash seems to have influenced the amount of opportunist non-native sycamore seeding in to Scar Close. Being first on the scene and growing, is maybe the only factor in occupation between those two trees, and is given weight by the Initial Floristic Composition Model of Frank Egler (42). He noted that those late-successional species already present in the seed bank or arriving shortly after a disturbance event were able to establish in sufficient numbers that later arrivals were not able to change the course of community development (essentially a priority effect).
I suppose some may argue that the halt to ash growth comes at the right time to stabilise the extraordinary floristic variety on this pavement, which could change if the trajectory to eventually greater canopy cover continued. This is the pretty banal argument of those who wish to manage everything, and was unsurprisingly articulated by Tony Whitbread, chief executive of Sussex Wildlife Trust, during an interview on ash dieback on the Today program of Radio 4, that the space created by the loss of ash trees would be good for biodiversity (43). Of course, that would be the biodiversity he chooses, rather than nature's choice. Whitbread banged on about the 1987 storm in the south-east of England, again, as he had done on the 25th anniversary, claiming that it had shown him that storms alone, in pushing over trees, do not cause enough disturbance to create the conditions for all our native wildlife, and so intervention management such as livestock grazing as a naturalistic system had to make up for that (44). He did so again on the 30th anniversary (45).
nonsensical argument was neatly punctured years ago, by Ted Green of the
Ancient Tree Forum (46). He pointed out that the interval between
occurrences of storms can often be centuries, although there was an
element of randomness in this interval, as there was in the location of
the storm and its severity and effect. This echoes George Peterken’s
review of the effect of wind on woodland, and particularly the periodicity
of storm events. He noted that the 1987 storm was one of five in the last
50 years, but that the last time a storm of comparable effect hit the SE
was in 1703 (47):
This randomness and uncertainty of location and effect led Green to quite rightly conclude that “It seems too unlikely that populations of grazing animals evolved to rely for survival on such unpredictable systems” (46)
there were more practical reasons why Whitbread’s notion of grazing
animals maintaining woodland areas opened up by storms was a nonsense. From the
evidence of the 1987 storm in southern England and the storm that hit
Northern France in December 1999, Green concluded that (46):
My argument would be that the nature of this particular limestone pavement deserves a better appreciation than that banal and oft-trotted out criticism of non-intervention, of creating “dense” shade. Firstly, ash in the north has probably one of the shortest seasons for clothing with leaf. The differential in terms of its shade impact, when compared to sycamore or beech is immense. There will always be a greater variety of light intensity within ash wood, and which favours not only ground flora but also a more extensive and varied shrub layer. Secondly, there are large areas of this pavement that are not jointed, and which will resist for much longer the growth of trees on the surface compared to in the joints. This also gives variety and more light from the open edges. I don’t think the blackthorn and elder that has returned would make a tree; nor will bird cherry or guelder rose that has also come back. The hawthorn also will not make much of a tree there because of climatic exposure. You can see the odd, relatively large sycamore on nearby grazed pavements. They are non-native, being mountain trees in continental Europe. They produce a much greater shade than ash, and would have a significant affect on the ground layer.
It is thus ash that has made this limestone pavement what it is now, and would continue to develop its interest in ways that we may not see now. If the seeding in of sycamore takes the place of ash, then all the floristic variety on Scar Close will be in danger. That is what the impact of ash dieback will be.
Mark Fisher 18 December 2012, 29 December 2012
The Joint Nature Conservation Committee (JNCC) commissioned research on the potential outcome of ash dieback to inform policy and decision-making (48). The hope is to have information to forecast the effect of the disease on species and ecosystems, and of different strategies for managing the disease. The research is to be completed by 31 March 2013, and so before a new season of infection will occur. This pretty much confines the research to what has happened in other countries, since while it is likely to have been in the UK for a number of years, no one was watching its progress.
The brief for the research poses a number of questions, and which I started to address above. Thus it asks for species that depend on, or are associated with, ash trees in whole or in part, and which will become threatened. They are particularly interested in threatened species that are considered of principal conservation importance, and what role ash plays in each of those species’ life-cycle. In what will become a controversial issue, it then asks which tree species could provide similar ecological functions in comparable habitats? Would these tree species spread naturally within woodlands or the landscape to fill the gaps, and what would be the likely change in community that would result? In perhaps the saddest question, because it relates to the future of Scar Close, it asks what would be the impact and problems that would arise from the loss of a complete group of ash trees.
It has already been proposed by Neil Sanderson, a freelance botanical surveyor, that sycamore would provide a potential bridging habitat for lichens until resistant ash populations develop (49). Sanderson, surprisingly, believes that sycamore is a close ecological approximation to ash (really? – see above). He argues that its absence as a British native is a chance result of the vagaries of postglacial dispersal, and thus he wants the “prevailing conservation attitude” changed to accept this tree species as an “honouree native”. Well, as many people have pointed out, there are no rows of sycamore lining the French coast, waiting to swim across, and there wouldn’t be as sycamore is mostly native to the mountains of Central and Southern Europe.
Sanderson is, of course,
primarily concerned with his own particular interests, especially lichens,
rather than woodlands per se, and that is why he is happy to see sycamore
preserve his lichens. He is credited with providing much of the
information for Plantlife’s disastrous publication that advocated the
brutalisation of woodland (50) and it is easy to see why from this, in his
report for Plantlife, and which slots him also into the prevailing
conservation attitude (51):
The management of woodland also comes up in the research questions, when it asks what effect general health has on ability of ash to withstand infection, and how other pressures, such as grazing by ungulates, air pollution, and root disturbance that affect tree health and regeneration, can modify the impact of the disease. Some recent research on ash dieback on Gotland, an island in the Baltic Sea off the Swedish mainland, provides some answers to this, and counteracts the managerialist edict of Sanderson. The study looked at ash dieback in woodlands under three management categories: unmanaged closed forest; grazed semi-open forest; and open traditionally managed wooded meadows with pollarding of ash trees, mowing and hay gathering (52). Dieback was least in unmanaged closed forests, and was most in traditionally managed open wooded meadows.
The emphasis of the research effort, as evidenced by the allocation of the funding available, is on the first group of questions, which could appear to foresee a future without ash, its place taken by other trees. This utilitarian attitude does little to assuage the sadness of those of us who will mourn their loss.
29 January 2013
(1) Dieback has affected 90% of Denmark's ash trees. Britain faces a similar threat, Tracy McVeigh, Observer 7 October 2012
(2) Dutch elm disease in Britain, Forest Research, Forestry Commission
(3) Brasier, C. (1996) New Horizons in Dutch Elm Disease Control. Reprinted from Report on Forest Research, Forestry Commission http://www.forestry.gov.uk/pdf/New_horizons_DED.pdf/$FILE/New_horizons_DED.pdf
(4) Ash dieback disease discovered in mature woodland in East Anglia, Fiona Harvey, Guardian 24 October 2012
(5) Ash dieback: government holds Cobra crisis meeting, Press Association, Guardian 2 November 2012
(6) Ash dieback found in Kent and Essex countryside, Adam Vaughn & Fiona Harvey, Guardian 5 November 2012
(7) Chalara dieback of ash - Questions and Answers, Forestry Commission
(8) Ash dieback: number of affected counties doubles, Adam Vaughn & John Vidal, Guardian 7 November 2012
(9) Ash dieback infection sites have doubled within a month, figures show, Damian Carrington, Guardian 6 December 2012
(10) Chalara dieback of ash (Chalara fraxinea). Forestry Commission (This webpage is updated for confirmed sites of infection)
(11) Government bans imports of ash trees, DEFRA News 29 October 2012
(12) Government ignored ash dieback warnings, emails reveal, John Vidal, Guardian 29 October 2012
(13) Ash Dieback (Chalara), Austin Brady, Woodland Matters, Public Affairs at the Woodland Trust 30 October 2012
(14) Guest blog – Ashes to ashes – Peter Marren, Mark Avery blog, 7 November 2012
(15) Ash dieback: lack of plant scientists blamed for slow response, Damian Carrington, Guardian 11 December
(16) Plant Health Act 1967 CHAPTER 8
(17) Forestry Act 1967 CHAPTER 10
(18) Chalara dieback - Key scientific facts, Forestry Commission 12 June 2012
(19) Rapid assessment of the need for a detailed Pest Risk Analysis for Chalara fraxinea, Forest Research 9 August 2012 http://www.fera.defra.gov.uk/plants/plantHealth/pestsDiseases/documents/chalaraFraxinea.pdf
(20) Chalara dieback - Key scientific facts, Forestry Commission
(21) Marco Pautasso. M., Aas, G., Queloz, V. & Holdenrieder, O. (2013) European ash (Fraxinus excelsior) dieback – A conservation biology challenge. Biological Conservation 158: 37–49
(22) Fisher, M., Carver, S. Kun, Z., McMorran, R., Arrell, K. and Mitchell, G. (2010). Review of Status and Conservation of Wild Land in Europe. Project commissioned by the Scottish Government
(23) Fraxinus excelsior. Associated invertebrates Database of Insects and their Food Plants. Biological Records centre
(24) Feeding and other inter-species relationships associated with Fraxinus (ashes). BioInfo: food webs and species interactions in the Biodiversity of UK and Ireland
(25) The Importance of Ash Trees to Lichens, the British Lichen Society
(26) Peterken, G. F. & Hughes, F.M.R. (1995) Restoration of floodplain forests in Britain. Forestry 68:187-202
(27) SteB1: Dieback has affected 90% of Denmark's ash trees. Britain faces a similar threat, Tracy McVeigh, Observer 7 October 2012
(28) Steb1's photostream, flickr
(29) Micheal Pocock, Centre for Ecology and Hydrology: Can ash dieback be stopped in the UK? Leo Hickman, Guardian 7 November 2012
(30) Steb1: Can ash dieback be stopped in the UK? Leo Hickman, Guardian 7 November 2012
(31) Maskell, L. et al (2012) Distribution of Ash trees (Fraxinus excelsior) in Great Britain from Countryside Survey data. NERC Centre for Ecology & Hydrology 6 November 2012
(32) Update - Ash dieback resources from CEH, CEH Science blog news, Centre for Ecology and Hydrology 7 November 2012
(33) Woodland Area, Forestry Statistics 2012 - Woodland Areas and Planting, Forestry Commission
(34) Common ash - fraxinus excelsior. Forestry Commission
(35) SteB1: Ash dieback disease discovered in mature woodland in East Anglia, Fiona Harvey, Guardian 24 October 2012
(36) National Vegetation Classification (NVC). Operations Note 4, English Woodland Grant Scheme, Forestry Commission 1 June 2008
(37) National Vegetation Classification: Field guide to woodland, Joint Nature Conservation Committee 2004
(38) Reintroducing lynx – sensing an atmosphere of wildness, Self-willed land February 2009
(39) Walking the wild places, Self-willed land September 2010
(40) Jönsson MT, Thor G (2012) Estimating Coextinction Risks from Epidemic Tree Death: Affiliate Lichen Communities among Diseased Host Tree Populations of Fraxinus excelsior. PLoS ONE 7(9): e45701
(41) Fisher, M. (2012) A review of naturalistic grazing versus natural processes. 11th European Wilderness Days meeting, Nauvu-Nagu, Finland 28 September 2012
(42) Egler, E.E. (1954). Vegetation science concepts I. Initial floristic composition, a factor in old-field vegetation development. Vegetatio 4:412-417
(43) Ash dieback 'beyond containment', Today Program, Radio 4 7 November 2012
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