Ash dieback began to spread in Europe in the 1990’s, reaching England in 2012.  It is a fungal disease that slowly but surely interrupts a tree’s ability to transport water.   The fungus responsible is Hymenoscyphus fraxineus, which is native to Asia.  The death / loss of mature trees not only reduces carbon dioxide uptake but also represents the loss of habitats for many species of insects and other animals.  The dead trees are also a hazard to people and property. Though many ash trees have now died after infection with this fungus, there is a small glimmer of hope on the horizon.  Some British ash trees are evolving a degree of resistance to the fungus.  Scientists from Kew and Queen Mary University of London have studied the genetic makeup of many mature european ash trees, and also hundreds of young saplings (at Marden Park in Surrey).   This revealed that resistance was more commonly found in young trees - a shift in the genetics of the trees within a generation.   The resistance to the fungus is NOT complete, but if these young trees make it to reproductive maturity then there will another chance for natural selection to ‘refine ‘ the process, through their offspring. However, it may be that a careful breeding program will be needed to establish true resistance / immunity. Interestingly, ash dieback has not reached America but the emerald ash borer has.  This insect is spreading and killing trees.  It is another example of the effects of the globalisation of world trade. Insects and other animals from across the world are being ‘mixed up’, moved from their native regions to new areas where they spread and cause damage as their predators and / or parasites have not travelled with them.   Trees and shrubs are now facing challenges and threats at an unprecedented rate. see also :  https://www.qmul.ac.uk/media/news/2025/science-and-engineering/se/british-ash-woodland-is-evolving-resistance-to-ash-dieback-.html  

I was born in the 1950s, a time when black smudges began to appear mysteriously on the trunks of sycamores in Britain. The culprit: sooty bark disease, a fungal infection caused by Cryptostroma corticale. Back then, I had no idea my life would unfold alongside a slow but steady parade of arboreal afflictions. But looking back now, I can measure the years not just in milestones and birthdays—but in the trees we lost along the way. Sooty bark disease doesn’t get the headlines these days, but it was a grim marker of post-war environmental change. Sycamores, long naturalised in Britain, would suddenly wilt and die, the bark flaking away to reveal a sinister black fungus. We didn’t yet understand how much stress—particularly from the hot, dry summers of the 1950s—played into its spread. It was an early sign: a warning that trees are far more vulnerable than they seem. Then came the true giant of tree diseases: Dutch elm disease. It began making headlines in Britain in the late 1960s and ravaged the landscape through the 1970s and '80s. Caused by a fungus (Ophiostoma novo-ulmi) spread by elm bark beetles, this pandemic decimated the native elm population. It’s estimated that over 25 million elms were killed in the UK alone. I remember the shift in the landscape. Once-common elm-lined avenues and hedgerows simply disappeared. As a child, I’d climbed elms in the park; as a young adult, I watched them vanish almost overnight. Dutch elm disease wasn’t just a biological tragedy—it was a cultural one. It marked a turning point, an awakening to the vulnerability of our treescapes. The decades ticked by. Chestnut trees became a familiar sight in my children’s drawings. But by the 2000s, I noticed the conkers looked smaller, sadder. Bleeding canker of horse chestnut, caused by Pseudomonas syringae pv. aesculi, began spreading rapidly across the UK. It causes a sticky, rust-coloured ooze from the bark and often leads to dieback and death. The disease didn't just affect the health of the trees; it diminished a cultural icon—conker tournaments and autumn walks lost something in its slow assault. Around the same time, sudden oak death (Phytophthora ramorum) emerged, though it affects more than just oaks. First identified in the US in the 1990s, it reached the UK in the early 2000s, causing widespread concern in woodlands and nurseries. It targets a range of species including rhododendrons, larches, and beech. The name alone—sudden oak death—carried a dramatic finality. Then came perhaps the most alarming of all in my later years: ash dieback, or Hymenoscyphus fraxineus. First identified in Poland in the 1990s, it reached the UK in 2012. It’s a true scourge, expected to kill up to 80% of the UK’s ash trees. These aren’t just forest trees—they line our roads, dominate hedgerows, shade our back gardens. Their decline feels intimate. Walking in ash woodland today is like passing through a ghost forest. The signs are unmistakable: leaf loss, crown dieback, diamond-shaped lesions. I’ve watched entire copses hollow out over just a few seasons. The cost is measured not only in timber or beauty, but in ecological networks—over 1,000 species depend on ash. And let’s not forget the oak processionary moth, which first arrived in the UK via imported oak trees in 2005. While not a disease in the fungal sense, it’s a threat nonetheless. Its caterpillars strip leaves and their tiny hairs can trigger allergic reactions in humans and animals. Forestry teams now issue warnings during their seasonal outbreaks. Oaks have stood proud for centuries, but even they are not safe anymore. There are others: sweet chestnut blight, plane wilt, the pine processionary moth, and new strains of Phytophthora that attack multiple species. The list gets longer, not shorter. So what’s going on? Part of the answer is globalisation. Trees, soil, and ornamental plants now travel easily between continents, bringing pathogens with them. Climate change plays its role too—stressed trees are more vulnerable, and warmer conditions allow pests and diseases to thrive. And while tree diseases aren’t new, our ecosystems today are more fragmented and less resilient. [caption id="attachment_8120" align="alignleft" width="400"] Leaf miner in Horse Chestnut[/caption]   What strikes me most, looking back, is how predictable this pattern has become. Every decade or so, a new name enters our vocabulary. Each time, we scramble to learn its symptoms, its vectors, its likely victims. And each time, the outcome is similar: loss, adaptation, then a wary lull before the next wave. Measuring my life in tree diseases might sound grim—but it’s also grounding. Trees are long-lived beings; their suffering unfolds slowly, deliberately. Watching them struggle is a reminder that the natural world is neither invincible nor immune to human action. The next great tree crisis is likely already on its way. But perhaps with better biosecurity, international cooperation, and public awareness, we can at least slow the tide. For me, though, the trees I’ve known—and the diseases that marked their passing—will always be a living calendar. A record of change, and of resilience.    

Various Wildlife Trusts are experiencing financial problems as a result of Ash Dieback.  Dead and dying trees are to be found in woodlands up and down the country, (some of which are managed by local Wildlife Trusts).    The fungus has its origins in Asia and has spread across Europe for the last thirty years. It was seen in Denmark in 2002, and has spread across the country by 2005.  It  is now to be found in  Austria, Belgium, the Czech Republic, Denmark, Estonia, Finland, France, Germany, Hungary, Italy, Latvia, Lithuania, The Netherlands, Norway, Poland, Slovenia, Sweden and Switzerland. It probably arrived here on imported (and infected) plants, though its spores are easily spread on the wind.  Once infected, the fungus affects the movement of water, minerals and sugars as the vascular system (xylem and associated tissues) is impacted.  Once a tree has been infected with the fungus, it may then be colonised by another pathogen such as the honey fungus (Armillaria spp).  Symptoms of ash dieback may include Shoot tips become black and shrivel, side shoots on young trees may die. Dead and ‘black’ leaves can be seen, their veins and stalks of turned brown.  Leaves shed early. Branches begin to dieback Diamond-shaped dark lesions form on the trunk near to dead side shoots.  In late summer, small white fruiting bodies can be found on blackened leaf stalks (see Jasper’s detailed blog). [caption id="attachment_39049" align="aligncenter" width="600"] the fungus emerging from blackened dead ash petiole.[/caption]   The dead and decaying trees pose a threat (as they become weakened and brittle), and need to be removed.  Removal is an expensive process and takes money from the Wildlife Trusts that would otherwise be used for habitat restoration, new planting etc. Apart from affecting the beauty of our woodlands and hedgerows, the loss of these trees has ‘knock on’ effects for other species.  Brown eared bats and barbastelle bats are known to nest in ash trees, the trees also provide perches and nest sites for birds and act as a substrate for epiphytes such as lichens and mosses.  The loss of ash tree will also affect the plants beneath, plants that like damp shady conditions such as lady fern (Athyrium filix-femina) and dog’s mercury; these may be replaced by light loving species / grasses. Featured image : Ash in winter Detailed information of Ash Dieback : https://cdn.forestresearch.gov.uk/2017/06/fcrn029.pdf [note this link downloads a PDF].  

They grow in dense overlapping tiers on dead stumps and branches, the felty topside of these semi-circular shelves primarily an orange to tawny brown colour demarcated to form zones of different colours, including a rather striking blue in places, and tending towards white at the edges. The Crimped Gill, or Plicatura crispa (also Plicaturopsis crispa), does indeed from such descriptions, sound remarkably similar to the Turkey Tails described in last month’s post. In these winter months when bracket fungi are plentiful in our woodlands, there are a good number of fungi that might be confused with Turkey Tails, in fact, from the False Turkey Tails and Hairy Curtain Crusts described last month, through the Tripe Fungus covered in a Fungi Focus from last February and other lookalike species such as the Smokey Bracket (Bjerkandera adusta).  Read more...

The woodlands blog has reported on the pathogen that causes ash dieback.   Jasper has described the nature of the fungus, and Richard has commented on how the problem has developed.   The disease has been variously referred to as  chalara,   ash dieback, and  chalara dieback of ash.  The fungus has an asexual phase, which was formerly known as Chalara fraxinea, hence the name of the disease; the sexual phase of the fungus was then associated with the asexual Chalara - this was called Hymenoscyphus pseudoalbidus. Putting the two together, the fungus was named Hymenoscyphus fraxineus (H.fraxineus).  The fungus Hymenoscyphus fraxineus is of Asian origin. Read more...

Recently, the IUCN (International Union for the Conservation of Nature) carried out a survey of the state of trees through Europe, specifically related to their risk of extinction.  There are some four hundred native tree species spread across Europe.   Trees are not just essential for life on Earth (generating oxygen through photosynthesis) but they also provide food and habitats for hundreds of species - birds, mammals, insects, spiders etc. The loss of tree species has considerable ‘knock on’ effects in terms of the biodiversity of an area. Trees also provide us with timber and other materials (cork, cellulose, oils). Read more...

We have now entered those glorious few weeks in the foragers’ yearbook when the proliferation of brambles across the country is at last yielding its fruits. For the bulk of the seasons, however, Rubus fruticosus can be viewed as little more than an annoyance, an invasive native with barbed, snaking canes that spread across pathways and woodland floors to form impenetrable thickets, snare up by passers-by and crowd out surrounding biodiversity (See ‘Native dominants or botanical ‘thugs’ in woodlands).  Or so it might seem. You will have probably noticed the tracks left by moth caterpillars munching on bramble leaves. Any blackberry-picker will also be well aware of the close association brambles seem to have with stinging nettles. Both attract a wide variety of insect life during their flowering months.  Deer and small mammals such as dormice, not to mention numerous bird species, are also the beneficiaries in terms of food and shelter of the bramble’s vigorous growth . Read more...

Members of the kingdom of the fungi can essentially be divided into the two basic categories of basidiomycetes and ascomycetes. The basidiomycetes form and release their spores on specialised cells called basidia, which can be found on the underside gills of our more familiar mushroom and toadstool-shaped types, or within the pores of boletes and brackets and suchlike.  Ascomycetes, however, produce their spores in the elongated cells known as asci that cover their spore releasing surface. Each individual ascus can contain usually around 8 spores, like snooker balls in a sock, which then get released out of the end when ready: the word is derived from the Greek for wineskin or sac. Typically we might think of cup fungi, such as the various members of the Peziza genus, like the Blistered Cup (Peziza vesiculosa) depicted here, whose favoured substrates of well-rotted manure or compost heaps lends has led to its alternate common name of the Common Dung Cup.  Read more...