A Fungus on a Fallen Tree
“I can smell them,” said my companion as we walked purposefully across my land in the UK’s Lake District.
I looked at him in disbelief. “What! Fungi? Did you say you could smell them?” I asked, my tone incredulous.
My companion both nodded and shrugged. Smelling fungi was, to him, quite normal. “I am not smelling them here,” he added.
I believed him, as he had been brought up in the wooded countryside of the Czech Republic, so what he did not know about fungi was barely worthwhile. My sense of smell has long been appalling, so I was prepared to believe that the rest of the world could likely smell a fungus, and I was the odd one out. If my companion could not smell fungi, they were unlikely there.
It was towards the end of the year and Nature had responded to the milder, wetter conditions encouraged by headlong climate change. The reaction of mankind to its changing weather was akin to driving a car full speed at an immovable dry-stone wall. Lots of chat, plenty of understanding comments, but action was closer to zero than zero itself.
The 2024 climate-change losers had been butterflies and other insects. The winners were trees, heather, grey seals, and, if the National Trust were to be believed, fungi. You could have fooled me for fungi, unless you were a crimson waxcap (Hygrocybe punicae), as they had been springing up in unlikely places, often on the shadier sides of fells. Although the waxcap is said to be edible, and rare, I will generally avoid eating it if I can.
For me, 2024 was a bad year for Lake District fungi. The region is widely known for its rich fungal diversity, yet I saw fewer than expected. The downturn could be attributed to several interrelated factors, including climatic influences, environmental changes, and human activities.
Climatic Influences
Fungi are susceptible to climatic conditions, with temperature and moisture levels playing pivotal roles in their development. The year 2024 had brought atypical weather patterns to the Lake District and disrupted the delicate balance required for fungal proliferation. The early months of the year had been marked by persistent rainfall and strong winds, saturating soils and reducing oxygen availability. These had hindered fungal growth. Moreover, soil saturation could have led to a shift in the microbial communities that would suppress fungal development.
As the year went by, temperature fluctuations further stressed fungal habitats. Cool, erratic weather during the spring months disrupted fruiting cycles, as fungi require stable moisture and temperature conditions to thrive. These inconsistent conditions contributed to a reduced number and lesser diversity of fungal fruiting bodies during the peak foraging season. The prime foraging season for many mushrooms is during May to June, when the warmer temperatures and increased rainfall typically create ideal conditions for fungal growth. Another excellent time for mushroom foraging is during September to November, when the cooler temperatures and moisture after the summer months traditionally stimulate fungal growth. Sadly, there is nothing traditional about climate change.
Environmental Changes
Broader environmental changes have pressurised fungal populations. The Lake District’s ecosystems are changing thanks to many factors, including pollution, habitat modification, and climate change. Time and again, climate change features. It affects almost all, if not all aspects of life, environment, indeed mankind’s very existence.
A significant worry is the decline in biodiversity within the Lakeland region. Studies indicate that reducing habitat diversity leads to losing the symbiotic relationships essential for certain fungal species. For example, mycorrhizal fungi, which form symbiotic relationships with plant roots, are particularly vulnerable to disruptions in biodiversity. Many fungi infect the roots of plants by creating an association with plants called mycorrhiza. This is a non-disease-producing association in which the fungus invades the root to absorb nutrients. Mycorrhizal fungi establish a mild form of mutualistic parasitism so that the plant and the fungus benefit from the association. About 90% of land plants rely on mycorrhizal fungi, especially for mineral nutrients (e.g. phosphorus), and in return the fungus receives nutrients formed by the plant. During winter, when day length is shortened and exposure to sunlight is reduced, some plants produce few or no nutrients and thus depend on fungi for sugars, nitrogenous compounds, and other things. The fungi can absorb these from waste materials in the soil and by doing so, can keep the host alive.
The degradation of temperate rainforests, crucial habitats for many fungal species, has exacerbated the problem. The decline of these rainforests in the UK is well-documented, with numerous fungal species at risk of extinction because of habitat loss. Wales is a lesson in point. The recent State of Wales’ Rainforests report found that despite their critical role in climate mitigation and ecological resilience, most Welsh rainforest habitat was in an unfavourable condition, with many sites suffering from multiple compounding threats. As a result, the Alliance for Wales’ Rainforests (AWR) called on the Welsh Government to take immediate conservation action to protect these unique ecosystems.
The report highlighted the ecological richness of Wales’ rainforests, which host over 400 rare mosses, liverworts, lichens, and specialist birds and bats. These habitats are invaluable not only as biodiversity hotspots, but also as natural carbon sinks and nitrogen fixers.
The main findings of the report were:
- Ecosystem Degradation: Only 22% of rainforest sites surveyed were in good condition, and none were rated as “very good”. Invasive species such as rhododendron and ivy were present in 70% of the surveyed sites, with many sites also suffering from invasive insensitive grazing and air pollution. I am an enthusiast for rhododendron and ivy, but that is not the point.
- Threatened Species and Habitat: More than 536 lichen species depend on ash trees, now threatened by Ash Dieback. Nearly 20% of the UK’s mosses and liverworts are also at risk in these habitats.
- Fragmented Conservation Efforts: Only 12% of Wales’ temperate rainforests are legally protected. A stronger protected-sites network is vital to achieve Wales’ goal of protecting 30% of its land for Nature by 2030.
Human Activities
Human interventions have also played a role in the decline. Agricultural practices, particularly those involving high-input farming, often degrade habitats crucial for fungal growth by altering soil composition and introducing chemical contaminants.
Conversely, sustainable farming practices have demonstrated their ability to support biodiversity. For example, studies on low-input farming systems have shown increased fungal diversity and richness in managed landscapes. Encouraging such practices in areas surrounding the Lake District might quickly mitigate some of the pressures on fungal populations.
In addition, policies stemming from the UK’s Agriculture Act 2020 and the government’s 25-Year Environment Plan have introduced changes in land management practices. While these initiatives promote biodiversity, they can also inadvertently cause short-term disruptions in fungal ecosystems.
Conservation Efforts
In response to these challenges, various conservation initiatives have been launched to protect and restore fungal populations in the Lake District. For example, efforts to maintain perate rainforest habitatshave shown promise in preserving fungal diversity. Conservationists have also emphasised the importance of public awareness and sustainable foraging practices to minimise the human impact on fungal populations. Responsible interactions with natural environments can help safeguard fungi's ecological roles, from nutrient cycling to supporting plant health. In Nature, everything links to everything else. I am uncertain who said it first, but it is undoubtedly true that, “We need Nature, but Nature does not need us.”
Although my companion was unable to smell fungi, and there were only a few to find, when a fungus does appear it can frequently grow speedily. Fungi are also silent, they may communicate with each other, but a fungus is extremely easy to miss. The fruit, the bit you can see, can appear in a matter of days, sometimes overnight, and may not last for long. Meanwhile, plenty of fungal activity is still taking place underground or deep inside the trunk of a tree — both are a hive of activity. It was no surprise that I nearly missed the multiple shelf fungi that were quietly growing out from a fallen ash tree. Shelf fungi are often called bracket fungi and can cause decay and rot in the heartwood of trees and produce bracket-shaped fruiting bodies on the trunk or main branches. They can lead to weakening and even the eventual breakage or fall of affected trees. A bracket fungus is sometimes called a polypore.
There are many types of bracket fungus. Some are specific to a particular host and often of little importance. Important ones that may cause significant damage to trees include:
- Ash heart rot, caused by the bracket fungus Inonotus hispidus. This attacks Fraxinus (ash), Juglans (walnut), Malus (apple), Platanus (plane), Ulmus (elm) and other broad-leaved trees.
- Beech heart rots, caused by the bracket fungi Ganoderma applanatum and Ganoderma australe. These can attack a wide range of broadleaved hosts, especially Fagus (beech).
Bracket fungi all cause similar symptoms. These can be:
- External symptoms: the first external symptom of bracket fungus colonisation can be the appearance of the fruiting bodies on the trunk (at the base or higher up), or main branches. The fruiting bodies can be up to 60 centimetres (2 feet) in diameter and may be annual or perennial. This may be preceded by visible crown thinning and die-back, but not always. By the time a bracket appears there will usually have been extensive heartwood decay. Since decay weakens the wood, another symptom may be falling branches.
- Internal symptoms: the fungi may also cause either a white rot or a brown, often cubical, rot in the heartwood. Both are structurally weakening. In some cases, the tree becomes hollow and may remain stable, but decay can lead to weakening and eventual breakage, or wind throw. Foresters distinguish top rots, which affect upper parts, from root or butt rots which affect the roots and base of the tree. The latter, such as Meripilus giganteus (giant polypore, found mostly on beech), are particularly damaging because the whole tree may fall.
A Fungus on a Fallen Tree
Fungi are Nature’s quiet powerhouses. They recycle nutrients, break down deadwood, and connect ecosystems in ways mankind is only beginning to understand. The bracket fungus I nearly missed as I walked across my land was on a fallen Lakeland tree, likely an ash, and was more than just a pretty sight. It was an ecological signpost, and the climate-change bell was ringing loudly. These days, I find it hard not to think about climate when I see a fungus.
Fungi matter. Most people in the UK have probably seen a polypore, just as I saw on the trunk of the fallen ash. These bracket fungi attach themselves to dead or dying trees and play a vital role in breaking down lignin and cellulose, tough materials that make up wood. Yet polypores are more than simple decomposers. They are bioindicators that can reflect the health of woodland and how it is coping with stressors such as climate change.
Fungi like these thrive in specific conditions. They need the right mix of temperature, moisture, and deadwood availability. But as global temperatures rise and weather patterns shift, those conditions are changing, and so are the fungi.
Lakeland’s Ancient Woodlands
Lakeland’s ancient woodlands, and I have some on my land, are some of the most biodiverse habitats in the UK. They are also under pressure. Increased storm events, fluctuating rainfall, and rising temperatures are altering the region’s delicate balance. The polypore I saw on the fallen ash is part of this story, which goes roughly as follows:
· Deadwood Dynamics: Storms in the Lake District are becoming more frequent and intense, leading to more treefalls. On the surface, this sounds like a win for fungi, as more deadwood means more habitat, but it is not that simple. Large-scale disturbances destabilise ecosystems and make it harder for fungi to establish themselves. With changes in the speed of wood decomposition under warmer conditions, the entire carbon cycle is affected.
· Extended Fruiting Seasons: Warming temperatures extend the fruiting seasons of many fungi, including polypores. This leads to increased decomposition rates and can interfere with the competition between fungal species. Some fungi may thrive, while others, especially those reliant on cooler, wetter conditions, can struggle. Fungi that are primarily reliant on these conditions include fly agaric (Amanita muscaria), amethyst deceiver (Laccaria amethystina), turkey tail (Trametes versicolor), birch polypore (Fomitopsis betulina), waxcaps (Hygrocybe spp), fairy ring champion (Marasmius oreades), and many others, too. Unique to northern climates are bog beacons (Mitrula paludosa) and the orange peel fungus (Aleuria aurantia).
· Microclimate Matters: The Lake District’s woodlands are known for their humid microclimate, which can support a wide variety of fungi, even if 2024 was a bad fungal year. As rainfall becomes more erratic, with intense downpours followed by prolonged dry spells, this balance is disrupted. Moisture-loving fungi such as polypores find it harder to survive, which impacts their role in the ecosystem.
Fungi as Forest Health Barometers
Polypores do not simply break down wood, they are part of a larger story. They help regulate a woodland’s carbon balance, interact with insects and microbes, and even influence soil health. When climate change disrupts their lifecycle, it sends ripples through the whole ecosystem. For example:
- Carbon Cycling: Fungi decompose woody biomass, and release carbon back into the atmosphere. Changes in fungal activity, whether it is faster decomposition thanks to warmer temperatures or reduced activity because of drought, can tip the balance of carbon storage and release in forests.
- Species Shifts: Climate change favours some fungal species over others. Thermophilic (heat-loving) fungi are on the rise, while those that need consistent moisture are declining. Thermophilic fungi include shaggy inkcap (Coprinus comatus), chicken of the woods (Laetiporus sulphureus), Dryad’s saddle (Cerioporus squamosus), birch polypore (Fomitopsis betulina), King Alfred’s cakes (Daldinia concentrica), and so many more.
- Ecosystem Interactions: Fungi do not exist in isolation. Changes in their activity affect insects, microbes, and even plants. When fungal communities shift, so does the rest of the ecosystem.
The Bigger Picture
In my woodland and its fallen ash tree — there is plenty of deadfall — it was clear that the tree was not just a piece of deadwood. It was part of a global story about how woodlands respond to climate change. Fungi are key players in this narrative, which shows how ecosystems adapt, and where they are struggling.
Temperature Effects
Warmer conditions speed up fungal metabolism and wood decay, but they also create opportunities for invasive species. For example, Armillaria, a genus of pathogenic fungi, is thriving in many forests and disrupts ecosystems. Armillaria is a fungal genus that includes the Armillaria mellea species (honey fungus) that lives on trees and woody shrubs. Armillarias are long-lived and form the largest living fungi in the world. It so happens that its largest known form covers more than 3.4 square miles (8.8 km2) in Oregon’s Malheur National Forest and is estimated to be 2500 years old. Some species of Armillaria display bioluminescence, too. Honey fungi are regarded in Ukraine, Russia, Poland, Germany and other European countries as one of the best wild mushrooms. However, the fungus must be thoroughly cooked as it is mildly poisonous raw. Honey fungi can cause sickness when ingested with alcohol, so it is advisable not to drink alcohol for 12 hours before and 24 hours after eating this mushroom to avoid any possible nausea and vomiting. In the UK, several species of fungi can cause adverse reactions when consumed with alcohol. These reactions are often because of the presence of compounds that interfere with alcohol metabolism, such as coprine or other toxins. Other examples of fungi that mix badly with alcohol are the common inkcap (Coprinopsis atramentaria) and the shaggy inkcap (Coprinus comatus).
Water Woes
Fungi need water, but just the right amount. Changing rainfall patterns are throwing this off balance. Prolonged droughts stress fungi, while heavy rains can wash away spores or create unfavourable conditions for growth.
Shifting Seasons
Longer fruiting seasons might seem a good thing for fungi, but they also disrupt established rhythms in the ecosystem. Earlier fruiting can affect interactions with insects, plants, and other fungi.
Thoughts for the future
Although 2024 appeared a bad year for fungi on my land, their paucity made me think plenty about them, and I soon realised how critical they are to a woodland ecosystem. Conserving fungi is not just about protecting biodiversity, it is about maintaining the health and resilience of woodland. For the future then, I had the following in mind:
- Leave Deadwood: Fallen trees and branches are critical habitats for fungi. It makes sense to leave them in place, as this supports not only the fungi, but the entire ecosystem.
- Monitor Fungal Communities: I must pay closer attention to my fungi and record both what I see and what I do not. Such long-term studies can help understand how fungi are responding to climate change and what that means for woodland health.
- Integrated Conservation: I must somehow protect my fungi as part of my broader woodland management plan. I must focus on any fungal resilience to climate stressors.
Conclusion
It was clear that the polypore on the fallen Lakeland ash was more than a simple, fascinating find. It was a window into how my land’s ecosystem is changing. Next time I see a fungus, and despite their 2024 paucity there are still plenty, I will stop and think. There is more to a fungus than I once thought.
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Published on The Bit Outside (www.thebitoutside.com) on 13 January 2025, where a full list of references may be found.
