Urban fungi foraging; how wood chip and pollution affects our mushrooms
- Credit: Archant
Walking through a local estate, on one of those steel-grey November mornings that have characterised so much of this autumn, I was interested to see a few late mushrooms growing amongst the Hebe in a shrub bed.
They were much gnawed by slugs but still recognisable as the false chanterelle. You may be familiar with the true chanterelle; the ‘ girolle’ . With its beautiful egg-yolk yellow and its fragrance like apricots, it is one of the most prized of edible mushrooms.
The false chanterelle is unrelated but draws its name from its superficial similarities. It is also yellow, though of a darker and more orangey tone, and both mushrooms have what are called ‘decurrent’ gills, running part way down the stem to give them a funnel-like appearance. The false chanterelle also, to my mind, has a rather pleasant and slightly fragrant smell, but not nearly so marked as the girolle.
According to my much loved Roger Phillips book of mushrooms, the false chanterelle is "said to be edible but has been known to cause alarming symptoms, such as hallucination, in some cases". I have, in the spirit of science, tried it just once, and to no ill effect, but have always refrained from feeding it to my family.
Since this is primarily a mushroom of coniferous woodland, the surprise was not just that it was growing in November, but that it was growing on an urban shrub border. The answer was quite simple, for it was growing from a mulch of wood chip, presumably from a pine or other softwood.
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The growth in the horticultural use of wood chip has brought a number of new species into our cities and I have fond memories of several times collecting the deliciously edible morel, a highly prized mushroom that resembles a brain on a stick. I have not only found it in parks and gardens, but once in an Islington school playground where I cooked it up for the staff. Due to the increasing importation of exotic plants, these wood-chip mushrooms even include species completely new to the country. The ‘redlead roundhead’, for example, a highly distinctive species with a bright orange-red cap, arrived here from New Zealand, and I once remember finding it in a large plant pot inside the Finsbury Park branch of City and Islington College.
Larger fungi like these obtain their nutrients through one of three methods. The mushrooms on wood chip are clearly acting as saprophytes; feeding on, and breaking down, non-living organic matter.
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Fungi can also function as parasites but the majority of them feed through a process of symbiosis, sending out networks of subterranean threads that penetrate the roots of trees and then partake in a mutual sharing of nutrients.
I mention all this because it affects the sort of fungi you might come across in an urban area. Trees and shrubs use their relationship with fungi to help break down compounds containing organic nitrogen, which might be otherwise difficult to obtain. In cities like ours, however, there is a very high level of nitrogen deposition in the soil arising from car exhaust and other sources. It means that urban trees allocate more nitrogen to growth - in leaves and shoots - and need to store less in their roots. Which means in turn that the fungi have less nitrogen to feed on and we see less of the mushrooms that form their fruiting bodies.
There is another estate near me, fronted with a lawn where each year I surreptitiously gather shaggy ink caps. They first appeared, in great quantity, when the area was being returfed.
Year on year, however, they have been declining. My guess is that having arrived with the imported soil they have been falling prey to this nitrogen problem and are unable to form a mycorrhizal relationship with the surrounding trees.
What it illustrates is the fabulous and fragile network of living things and the complexity of the unseen relationships between them. It also demonstrates the unforeseen environmental impacts of our actions and how far we have to go if we are to establish a truly biodiverse city. Frankly, if things get much worse, I might have to start eating the false chanterelles.