In spring 2024, fungi enthusiast Heather Clarke was foraging near an ancient woodland in northern England when she spotted hundreds of bright yellow mushrooms carpeting the length of a fallen log. This is one of two confirmed sightings of golden oyster mushrooms in the UK, which have spread explosively throughout 25 states in the US in recent years, introduced there through small-scale growers and hobbyists. Following this recent sighting in the UK, the fungus has this week been declared a high-risk invasive species by the UK government, joining Japanese knotweed, grey squirrels and other notorious interlopers.
If the golden oyster mushroom takes hold in the UK, mycologists fear that it would outcompete native fungi, disrupting ecosystems and harming biodiversity. Climate models are now being used to find out how quickly it could spread throughout the UK, Europe and beyond. What’s more, there are signs that hobbyist breeding programmes may have supercharged the fungus’s ability to multiply, leading mycologists to call for a rapid response to the incursion.
The golden oyster mushroom (Pleurotus citrinopileatus) is a prized edible mushroom, foraged from the wild in its native range of East Asia and eastern Russia. It is also cultivated across this region, where it is enjoyed in soups and stir-fries and has been recognised in modern research as having potential health benefits, including antioxidant properties. But in recent decades, golden oysters have also been widely cultivated in the US and elsewhere.
In the early 2010s, the species escaped into the wild in the US, quickly expanding from these niche cultivations to a continent-scale invasion now spanning some 2 million square kilometres. The events that followed in North America suggest what might be in store for the UK, too. A study published in August by Veerabahu and her colleagues found that its aggressive colonisation excludes dozens of different native species from wood in typical habitats – with the share of wood colonised by some species reduced by as much as 55 per cent.
Shifts on this scale disrupt processes such as nutrient cycling and the symbiotic relationships fungi have with other organisms, such as trees that collaborate with particular fungi species to access nutrients, and insects that rely on native fungi as a food source or breeding habitat. Golden oyster mushrooms are also known for having a particularly ravenous appetite for deadwood. This allows them to fruit rapidly (mushrooms are the temporary fruiting bodies of a fungus) and produce many spores that reach newly available wood before their competitors.
Once established, their fast growth also allows them to fully colonise the woody substrate quickly, giving them an advantage over slower-growing native fungi. The speed with which they decompose wood destroys deadwood habitats relied upon by already threatened insects such as the European stag beetle, whose larvae rely on slowly decaying hardwood as they develop over several years, as well as other animals and tree seedlings. What’s more, the rapid decay of deadwood releases carbon dioxide into the atmosphere quickly, reducing how much carbon is stored in the forest long-term – and further harming Earth’s already faltering carbon sinks.
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