Coastal Hazelwoods and their Lichens

Following the 1997 NWDG Field Meeting, at which coastal hazelwoods were one of the main subjects, we felt it appropriate to reiterate here the importance of this much overlooked habitat and the remarkable lichen flora that it supports. Apart from the recent campaigning on behalf of hazelwoods by Peter Quelch, documentation of their importance for lichens is hidden in specialist lichenological journals and unpublished survey reports.

Having few if any larger, emergent trees, coastal hazelwoods can easily be dismissed in a rather derogative manner as 'mere scrub'. In reality, these woods can vary from being recently invasive scrub over former rough pasture through to ancient woodlands of long continuity. The former can usually be identified from recent documentation, photographs, or discussions with local people, but recognition of the latter is much more difficult as little, sufficiently detailed documentation (apparently?) exists from former centuries. However, from the studies pioneered by Francis Rose, the use of lichens as indicators of ecological continuity is becoming widely appreciated. By adapting the methodology and arguments employed originally for oak-dominated woodlands to hazelwoods, 'hot-spots' of high biodiversity with a large number the more demanding species become apparent. Such 'hot-spots' so far identified can be found on the Morvern coast, the Ardnamurchan peninsular, Eigg, south Skye, and further south at Ballachuan on Seil. These are mostly wind-clipped woodlands close to the sea, although a few examples occur slightly more inland in valleys - the prime example being parts of the Resipole ravine where the hazel is dominant and not over-topped by larger trees.

The lichens inhabiting the hazelwoods form two broad phytogeographical categories (alliances) - the Lobarion pulmonariae ('Lobarion') and the Graphidion scriptae ('Graphidion'). The Lobarion, in its various facies, is the climax, lichen-dominated community of deciduous trees of old forests in temperate regions, whereas the Graphidion comprises crustose lichens that often predominant on smooth bark where establishment of the Lobarion has been prevented or not yet occurred.

The Lobarion

Walking in from the exposed, seaward edge of the woodland, it is the large, often leafy or dark and spongy species of the Lobarion that catch the eye. The larger, leafy (foliose) lichens belong to the genera Lobaria, Nephroma, Peltigera, Pseudocyphellaria and Sticta, those with a more adpressed habit and small marginal lobes to Degelia, Pannaria and Parmeliella, and those with a blackish, jelly-like consistency when wet to Collema and Leptogium. All of these lichens have cyanobacteria ('blue-green algae') as their main or secondary photosynthetic partner. In those with a predominating green algal partner, the cyanobacteria are confined to specialized structures (cephalodia) on or within the lichen thallus, e.g. Lobaria amplissima and L. pulmonaria respectively. The cyanobacteria fix nitrogen from the atmosphere, so that these lichens must make a major contribution to the nitrogen economy of the woodland ecosystem.

Lichens of the Lobarion are conspicuous and prolific in the oceanic, almost pollution-free climate of the Western Highlands, sometimes inhabiting secondary habitats (e.g. policy woodlands) and coastal rocks away from the influence of tree cover. One could be forgiven for thinking that these species all belong to a strongly oceanic (euoceanic) biogeographical element, but this is not altogether true. Several of them are (or were) of wider distribution, though more confined to ancient forests, occurring well into Central or Eastern Europe. Such 'suboceanic' species include all the four British Lobaria spp., Collema fasciculare, Leptogium cyanescens, Pannaria rubiginosa, Peltigera collina and Sticta sylvatica. The oceanic bias in their distribution has been accentuated by the affects of widespread atmospheric pollution, forest clearance and unsympathetic forest management. The more strictly oceanic (euoceanic) species of the Lobarion found in the hazelwoods include Degelia atlantica, Leptogium brebissonii, L. burgessii, Parmeliella testacea, Pseudocyphellaria crocata, P. intricata and P. norvegica.

The Graphidion

Once accustomed to the luxuriance of the Lobarion community, the observer's eye might then fall to the 'bare' surfaces on younger stems or amongst the Lobarion lichens and associated bryophytes on the larger stems. Closer inspection, especially if aided by a hand lens, will reveal virtually no truly naked bark but a complex mosaic of variously coloured, though predominately whitish to pale brownish patches, each often delimited by a dark line. Most of these patches will have numerous fungal fruiting bodies, seen as black dots (e.g. Arthopyrenia, Pyrenula), dashes (e.g. Arthonia, Arthothelium), jam tarts (Lecanora), black discs (e.g. Bactrospora, Lecidella) lines resembling Arabic script (e.g. Graphis), or as pores in the surface (Pertusaria, Thelotrema). The thallus of most of these species grows within the surface layers of the bark, and in all cases has only a green alga as its photosynthesizing partner. In many cases, if the thallus is scratched, the algae are seen to be orange - the cells of such algae contain large quantities of carotenoids and belong to the genus Trentepohlia.

Like the Lobarion, the Graphidion is represented well into Central and Eastern Europe in areas of ancient forest. However, in these more continental regions even a well-developed example is unlikely to comprise more than a dozen species, contrasting with the situation in W Scotland where the better examples have about 50 species, with a strongly represented euoceanic element. In the British Isles, the Graphidion is best developed on hazel, but good examples can be found also on, for example, holly and rowan, and branches or young stems of ash and oak. Euoceanic lichens, i.e. confined to the Atlantic seaboard between SW Norway and Macaronesia, include Arthopyrenia carneobrunneola, A. nitescens, A. viridescens, Arthonia ilicina, Eopyrenula grandicula and Mycomicrothelia confusa. Similarly distributed but very rare or absent in England and Wales are Arthothelium orbilliferum, Bactrospora homalotropum, Melaspilea atroides, Pyrenula occidentalis, Thelotrema macrosporum and T. petractoides. Eopyrenula septemseptata is known only from SW Norway and W Scotland, and Arthothelium macounii only from W Scotland and British Columbia. Apparently endemic to W Scotland and W Ireland are Arthonia ilicinella and Mycomicrothelia atlantica, while Arthothelium dictyosporum and Graphis alboscripta are so far known only from W Scotland. The conspicuous Parmentaria chilensis, with its large, thick and waxy, yellowish thallus and clusters of immersed black fruiting bodies that can been likened to ìblackberries floating in custardî, is confined in the British Isles to the Resipole ravine and a few sites in SW Ireland, occurring further afield in Macaronesia, Jamaica, Colombia and the Pacific Island of Juan Fern·ndez, off the coast of Chile.

Associated Organisms

Lichens do not stand alone in the ecosystems in which they occur, and there are many interactions with other organisms. In the hazelwoods, Lobarion lichens are often seen to become first established on bryophyte mats, which they may later overgrow almost entirely, and their contribution to the nitrogen economy has already been mentioned.. Lichens are a source of food and shelter to many invertebrates, and are hosts to many, often specialized fungal parasites. Many of these parasites are host species-specific, and obvious examples of those that must be very rare are Arthonia cohabitans on Arthothelium macounii and Opegrapha brevis on Thelotrema petractoides. The possibility of there being similar close associations at the 'species to species' level between lichens and invertebrates is a line of research awaiting attention.

During our surveys of hazelwoods we have encountered several rarely reported, non-lichenized fungi. At Morvern, these included Chromocyphella muscicola, the fruit bodies of which form delicate clusters of bell-shaped cups on Frullania. Also found was the spectacular, somewhat 'spooky', Hypocreopsis rhododendri, whose lichen-like stroma have radiating lobes that grasp the hazel stems like on orange gloved hand! In Britain, it is known only from some of the very best, lichen-rich hazelwoods. It is surely reasonable to suppose, that a closer study of these ancient hazelwoods by invertebrate specialists and mycologists will add the uniqueness of the habitat already evidenced by lichens and these two examples of rare fungi.

Management and Conservation

The lichenological evidence from the 'hot-spot' hazelwoods clearly indicates a long history of continuity. That is not to say that such woods have been 'untouched'. On the contrary, several of them are close to, or even on, the sites of former habitation, and it is probable that their value to local communities as shelter for stock and as a source of wood for various purposes has ensured their survival over the centuries. Aspects of past, present and future management of coastal hazelwoods will be treated more fully in a forthcoming publication by Peter Quelch, but in general it can be said that these woods require little attention to maintain there present structure and biodiversity. Given freedom from continual overgrazing by sheep and deer, and excessive shading from emergent trees or the planting of adjacent conifer plantation, the hazels will perpetuate themselves without any need for coppicing. Indeed coppicing, at least on a large scale should be avoided, as it interrupts the continuity of age range of stems and the succession of colonization from the Graphidion to the Lobarion. The more noteworthy and demanding species are slow to colonize new areas, such that extensive coppicing can, in one cut, destroy an ecosystem that will have taken several centuries to evolve.

Much remains to be learned about the history and natural history of coastal hazelwoods, but it is clear that they represent a distinctive habitat deserving recognition in terms of vegetational classification and priorities for conservation. The habitat is almost unique to W Scotland, with a few examples in W Ireland, and its absence from both the National Vegetation Classification and the European Habitats Directive are two matters requiring redress.

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