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Caithness Field Club Bulletin
|Biodiversity and Fungi Conservation
(by David Savage)
Biodiversity is one of the major tools for habitat conservation. The following are a few personal thoughts on how a biodiversity approach may help towards fungi conservation, and how fungi biodiversity can indicate habitat health.
First it is necessary to consider what fungi are and how
they fit into the wider biosphere:
Fungi life style.
Fungi for the most part are hidden from view. The mushrooms and toadstools that can be transiently so obvious during autumn are their fruiting bodies. The millions of spores released by these fruiting bodies (termed sporocarps) are normally wind dispersed. Under appropriate conditions the spores germinate to produce microscopic threads (hyphae), which can grow to invade large areas of a suitable host. Before most of the larger fungi can produce a new generation of fruit bodies two of the hyphal growths, of differing sexual types, must first merge into a common organism. ( many of the microscopic fungi can also reproduce by a self cloning process.)
As fungi are only visible when fruiting it makes recording of them challenging. In this respect they differ markedly from plants, which with experience can often be located, identified and counted when not in flower, or birds, which may be highly mobile, but remain as distinct entities that can be individually identified (by ringing for example) and even tracked over long distances by using satellite transponders.
A further difficulty with fungi recording is the irregularity of fruit body production, which in some cases may be very infrequent. Just what triggers fruiting is not totally clear. Although moisture is normally a requisite of fungi fruiting, it appears that stress, such as nutrient exhaustion, moisture shortage, or in response to heat, may also be necessary for many species. Therefore both weather variations from year to year and the local micro climate have an effect.
The immediate implication is that it is very difficult to know what fungi are actually present at a specific place. Observing transient fruiting bodies requires frequent visits, and will in general only pick up those fungi that fruit regularly. Soil DNA analysis can help, but requires specialised equipment. A further limitation is that the present state of knowledge only permits identification of a limited range of species from DNA data.
This rather uncommon animal is occasionally seen rummaging in the darker areas of woodlands during wet spells in autumn. In spite of their enthusiasm, many can only confidently identify a small fraction of the fungi they find. As a consequence the national database for fungi records is very patchy, and probably reflects the distribution of confident mycologists better than the distribution of fungi.
There are around 2000 gilled fungi in the UK, and a thousand or so other larger fungi. Many differ only in microscopic details. Because of variation within species there is still debate on realistic species limits, with splitters and lumpers unable to agree. Recently DNA studies have only confused the picture more, by finding close links between apparently very different fungi, and also showing that some apparently well defined species are in reality several unrelated species! Eventually clarification will occur, but at present even the best mycologist has his problems with correct identification of some fungi.
The larger fungi can be broadly grouped into 3 different habitat types.
[A] Many fungi fill a major roll in decomposing and recycling dead organic material Their precise habitat will depend on the enzymes they can use to break down plant structural matter or other organic materials, and the conditions under which those enzymes can work effectively. Some fungi can use a large range of plant types, and may be found in almost any moist plant remains. Some are capable of using only one specific component of a dead plant. This is particularly common with woody tree remnants, where a succession of fungi are involved in its gradual breakdown. Yet others are closely tied to specific plants. For example, there is a family of visually similar, but genetically and microscopically distinct, fungi which break down old, buried, conifer cones. One is confined to Norway spruce, just very occasionally occurring on Sitka spruce. One is confined to Scots pine, very occasionally occurring on some the other European pine species, but never on Lodgepole pines. A third species prefers some of the European pine species, but occasionally grows on either Scots pine or Lodgepole pine cones. Are you that capable at distinguishing pine species? I know that I have found them a challenge.
For many of the plant decomposers, maturity is quickly achieved and fruiting then takes place whenever moisture levels and temperature are suitable. Some of this type of fungi rapidly colonize (in weeks) suitable new habitat, but equally quickly exhaust its key component and then disappear.
Some fungi are only found in environments enriched in nitrogen, such as animal dung (and also the well fertilised lawn). Others cannot tolerate nitrogen enrichment. Similarly, the presence or absence in the soil of either calcium or acidity determines which fungi may be present.
Conservation of these essential litter decomposers can only be achieved by ensuring a regular supply of a suitable substrate. A healthy, varied natural environment is needed for the conservation of these fungi. Equally, the recycling of plant constituents is essential for a continuing healthy, natural, environment. Thus general biodiversity, coupled with restraint from tidying up any dead materials, is ideal. Long term fungal biodiversity may be a good indicator of how well this is being achieved. Short term large fruitings of a limited range of fungi may indicate that the natural balances have been disturbed. An autumnal visit to a recently clear felled area of a conifer plantation will provide a good illustration.
[B] A large proportion of the larger fungi live in an intimate, interdependent relationship with higher plants (mainly trees). The hyphae of these symbiotic fungi penetrate the walls of the plant's roots, permitting the mutually beneficial exchange of minerals extracted from the soil by the fungus and plant sugars produced by photosynthesis in the tree. Generally these mycorrhizal fungi are totally dependent on a single family of trees. Obviously conservation of the host tree is essential in the conservation of such fungi.
The fruiting patterns of symbiotic fungi are very different to the decomposers/recyclers. Their key food source is replenished on a seasonal cycle, as their host plant grows, consequently a seasonal fruiting is commonplace. However many fungi fruit only occasionally though this is not always obvious in an extensive woodland, as different colonies of a common species may fruit in different years, and so seem to be regularly present. But it can be seen by long term observation of the often lone birch trees dotted around the Pennyland estate in Thurso, where the same fungi appear each year, but often in different places.
There also seems to be a tendency for fruiting frequency to decrease as the tree partner matures. Conversely, time allows more fungi to colonize a particular habitat, this seems particularly so for the less common fungi. The rare tooth fungi of the old Caledonian forest make a well studied example. Confined exclusively to Scots pine growing on gravely soils, they are typically found with young trees growing (or planted) amongst very old trees, and normally only where the gravel has become exposed (often path sides or local gravel pits, but presumably around uprooted trees in a purely natural forest). Fruiting may be annual in a favoured location. However occasionally several different species may appear simultaneously, for just one year, in a new location. Obviously a common trigger is involved, and presumably the fungi is present with its host during the many non-fruiting years.
The logical deduction from this type of behaviour is that conservation of the mycorrhizal fungi requires both host diversity and continuity of presence. Conversely, mycorrhizal fungal fruit body variety is a better indicator of habitat health than fruit body numbers. Locally this is well illustrated by some of the birch woods, for example many areas of old birches in Dunbeath Strath produce few fungal fruit bodies in any one year, but with amazing variety over a longer time period, while areas of young birches produce more fruit bodies each year, but of a more limited range of species.
[C] Grassland fungi constitute the third major group. Some live on dead plant remains, and can be found in a variety of grassland habitats. They can quickly colonize suitable habitat. Many others are probably mycorrhizal with grasses, and are found in nutrient deficient habitats. Such habitats are usually flower rich. These are the fungi of most conservation interest as they are very slow to recolonize suitable habitat. As a consequence their presence is considered to be a good indicator of healthy and undisturbed grasslands. However, because of the more rapid colonisation by flowering plants, a flower rich habitat is not a reliable indicator of a good grassland fungi flora.
This slow rate of recolonisation means that conservation of habitat continuity is essential for the continued survival of these fungi. Unfortunately, the agriculturally poor grassland they depend upon is all too readily lost to "improvement", either agricultural or by afforestation, (some in the name of biodiversity, or "restoring" native forest), or "development" of marginal, "useless", land
Because of the close relationship between specific fungi and specific plants, a good general biodiversity is essential for varied fungi flora. Conversely, fungi variety is a good indicator of the general health of a habitat. However, large fruitings of a limited range of fungi are likely to indicate a recent disturbance to the balance of a habitat.
Conservation of fungi in general is best achieved by maintaining a balanced, varied, habitat. In particular, the current trend for the enthusiastic removal of dead or dying plant material is strongly detrimental to many fungi, and by eliminating natural recycling, is probably detrimental to long term habitat health. The grassland fungi are a particularly vulnerable group because of a slow recolonisation rate and the pressures on their habitat.
Appendix: Sites with good fungal biodiversity.
Dunnet forest, ND 225700:
Achvarasdal wood, NC 964 648
Un-named wood, Helshetter Strath, NC 962 607
Dunbeath Strath birch woods.
The following woods look likely to have good fungal diversity, because of there age or wide variety of trees, but I have not (adequately) visited them: Sandside wood, NC 952 650, Berriedale wood, ND 115 225, Langwell Strath birch woods, ND 075 227 and ND 055 230
Dunnet/Greenland links, ND 227 695
Crosskirk to Ushat head, ND 031 699 to ND 033 708
Brawlbin, ND 077 580
Westerdale Bridge, ND 130 518
Dunbeath Strath, ND 144 306
Helshetter Strath, NC 962 620
Loch Watten (Lynegar) ND 216 572
Yarrows, ND 305 433
Various other areas of rough gazing around Caithness host grassland fungi, but they are often small remnant patches between formerly cultivated areas. Other promising looking areas have not been visited at an appropriate time.