Diversity

Note: For more information and illustrations, take a look at chapter 4    of the free Scottish Natural Heritage publication 'Atlantic Hazel'.

The unique climate and long history of hazel woodland cover has resulted in a habitat that is rich in species, many of which are rare or absent elsewhere in Europe.

Lichens

Lichens are probably the most defining species of Atlantic hazel. Their diversity is internationally important, with some species such as the white script-lichen Graphis alboscripta only occurring in Scotland. If you look at the British distribution  of many of the species mentioned below (e.g. Yellow specklebelly  ), you will see that many are mainly, if not entirely, restricted to the west coast of Scotland. This diversity is partly due to the climate and long history of woodland cover along the west coast, but also due to the variation from young smooth bark to old rough bark - each of which supports a different group of lichens.

Young hazel stems have smooth bark, and when they grow rapidly, straight up to reach a gap in the canopy, they are the characteristic "hazel" colour. Some of the earliest colonizers of smooth hazel bark are hardly lichens at all, but small bark fungi that use the chlorophyll in the bark cells of the hazel for their food. Sometimes, these hardly discolour the host bark at all, and it is only the tiny blackish dots and dashes of their fruits that reveals their presence. The species come from groups (genera) of fungi such as Arthothelium (e.g. Arthothelium macounii), Arthopyrenia and Tomasellia.

The next colonisers of young smooth barked stems are small crusty species. These are 'true' lichens, in that they are both a fungus and an alga combined, i.e. they have their 'own' algae, and do not use the chlorophyll in the bark cells of the hazel for their food. Some have small fruits that are dark or pale dots, and others that are scribble-like lines. It is this last group (the 'script' lichens) that lend their name to this group of lichens called the Graphidion. Species include Melaspilea atroides, Thelotrema pectractoides, Pyrenula macrospora  and the rare blackberries in custard Pyrenula hibernica. Have a careful look at any young hazel stem on the west coast and you will see an almost continuous cover of these species! 

Another community of lichens tends to occur on rougher hazel bark of older stems, often with mosses and liverworts. Perhaps the most charismatic and best known lichen of Atlantic hazel is the large leafy-lobed lichen tree lungwort  Lobaria pulmonaria. This lichen lends its name to the community of Atlantic, leafy-lobed lichens called the Lobarion. Other distinctive species in this community include yellow specklebelly  Pseudocyphellaria crocata, plum fruited felt lichen Degelia plumbea, octopus suckers Collema fasciculare and frilly-fruited jelly skin Leptogium burgessii.

Mosses and Liverworts

The deep greenness of the mosses and liverworts, clothing rocks, trunks and leaning branches, climbing up the bases of hazel stools, provide the quintessential atmosphere of the 'Celtic rainforest'. Truly oceanic bryophytes require fairly constant levels of humidity in order to thrive, so generally are found in sheltered habitats and niches, away from bright sun or drying winds, and they are tolerant of low light levels. When entering a hazel stand, you become aware of "mossiness" only when you have penetrated a little distance into the stand, where the closed canopy forms a secure, sheltered and undisturbed habitat, ideal for the development of oceanic bryophytes.

Typically, the Atlantic hazelwoods boast a good diversity of mosses and liverworts with an abundance of the more common western species, but also many very special oceanic species are frequent. Perhaps the commonest moss on hazel in the western Highlands is dwarf neckera Neckera pumila , but other common mosses include the slender mouse-tail moss Isothecium myosuroides var. myosuroides, the common feather-moss Kindbergia praelonga, common striated feather-moss Eurhynnnchium striatum, short-beaked wood-moss  Loeskobryum brevirostre and the neat feather-moss Pseudoscleropodium purum. Oceanic (Atlantic) species typically include the frizzled pincushion moss  Ulota phyllantha and the lesser yoke-moss Zygodon conoideus, as well as the liverworts sea scalewort Frullania teneriffae, pointed pouncewort Harpalejeunea molleri, toothed pouncewort Drepanolejeunea hamatifolia, petty featherwort Plagiochila exigua and Killarney featherwort Plagiochila bifaria. More notably, two scarce oceanic species - the balding pincushion moss Ulota calvescens and the liverwort minute pouncewort Cololejeunea minutissima - grow mainly on western hazels.

Fungi

Although there are many fungi that are recorded as growing in association with hazel, there are relatively few that are specific to hazel itself. Hazel is ectomycorrhizal, which means that it grows in a close (symbiotic) relationship with certain fungi: the fungi are intimately associated with the roots of the hazel, and enable the tree to take up nutrients which help to enhance its growth. In return, the fungus receives excess sugars from the hazel, enabling it also to thrive.

Fiery milkcap Lactarius pyrogalus is the most common mycorrhizal hazel associate. When damaged, this species exudes a fiery-tasting milky-substance! Another large toadstool that is recorded with hazel in Scotland is the hazel bolete Leccinum pseudoscabrum, with tubes under the cap rather than gills and flesh that blackens on exposure to air. Mycorrhizal fungi are often sparse in hazel woodland. It has been suggested that soils characteristic of hazel woodland (known as mull humus, due to plant remains being successfully broken down by small creatures in the soil, including plenty of earthworms) support both less species and lower fruit body production than mor soils (mor soils are associated with acidic conditions such as coniferous woodlands or acid moorlands, where cool, wet climatic conditions support fewer soil fauna, so the organic matter is not broken down so quickly).

Sometimes, you can be lucky in hazelwoods and discover some rarely reported fungi. At Morvern, Atlantic bells Chromocyphella muscicola has been recorded, the fruit bodies of which form delicate clusters of bell-shaped cups on the reddish-brown, leafy liverwort Frullania. Another unusual fungus is the striking scarlet elf cup  Sarcocypha austriaca, a distinctive orange-red cup fungus, growing in the spring on fallen twigs and branches in leaf litter.

Winter storms will damage the canopy, breaking off twigs, and abrasion from stems rubbing together in windy weather allows fungal pathogens to get a hold and gradually kill off individual stems. This all leads to a considerable turnover of stems within the stool. The fascinating glue fungus Hymenochaete corrugata has the ability (otherwise found mostly in the tropics), to 'glue' together and trap dead, fallen twigs that get lodged against living stems in the hazel stool, so preventing them from falling to the ground. This enables the fungus to feed on the dead wood, avoiding competition from other saprotrophs on the woodland floor.

Although occurring far less frequently, it is thought that the radiating lobes of hazel gloves  Hypocreopsis rhododendri are in some way closely associated with the glue fungus, and may even be parasitic on it. Hazel gloves is a conspicuous species, which somewhat resembles a lichen in that it forms thick, rubbery orange rosettes, reminiscent of minute orange washing-up gloves, with fingers or radiating lobes that clasp around the hazel stems. The species is thought to be an indicator of old growth hazel woodland and its presence puts you firmly in an Atlantic hazelwood habitat.

In western Scottish hazel-dominated woodland, the ground vegetation is varied. The commonest type is a mixture of grasses, flowering plants and bryophytes. In many places, especially on limestone, the ground vegetation is less grassy and more dominated by flowering plants, and these hazelwoods are the extreme north-western representation of the broader ash - rowan - dog's mercury woodland type, which can develop in exposed situations in the windy far north-west of the British Isles.

Dogs mercury, and bluebell, are both common in these woods in the spring and early summer. Other species which can be found include enchanter's nightshade, wood sorrel, wood anemone, wood avens, false brome, primrose, and common dog violet. Species such as melancholy thistle and globe flower give a distinctly "northern" feel: Ferns are often present: male fern, lady fern, bracken and hard fern to name but a few. More localised lime-loving ferns which may also be found include regionally unusual plants such as hart's-tongue and maidenhair spleenwort or, at a higher altitude, the less common green spleenwort.