Corylus avellana scrub

This is permanent scrub dominated by Corylus avellana mostly typical of exposed coastal and upland situations with a humid Atlantic climate. The hazel forms a low canopy up to 3m tall, wind-shaped in more exposed situations, with multi-stemmed stools that are self-renewing by the production of new growth from the centre and slow clonal expansion. On shallower soils, stools tend to be more close-grown, with fewer thicker rigid stems and the scrub more shady; on deeper soils and in more sheltered situations, wider-spaced, multi-stemmed stools prevail with a lighter interior. Damage from winter storms also contributes to stem turnover and grazing/browsing can open up the canopy and prevent regeneration ultimately creating a parkland effect where older individual hazels can survive, sometimes acquiring a tree physiognomy.

The field layer varies according to the character of the soils which can be highly calcareous to slightly acid, shallow and skeletal to deeper and loamy and the often irregular topography favours complex mosaics with local instability of the surface. High precipitation usually maintains the soils in a moist condition, but local ground water seepage can further enhance wetness. The herb contingent is usually of the more Atlantic Carpinion type, more or less calcicolous according to the soil reaction, with an obvious vernal component in which Hyacinthoides non-scripta, Anemone nemorosa and Primula vulgaris often figure, and a sometimes luxuriant fern flora. Less limey soils can have a grassier flora with a summer cover of Pteridium aquilinum. Towards the north of the range, Trollius europaeus and Cirsium helenioides provide a distinctive phytogeographical element.

The cryptogam flora can be very rich and distinctive in less disturbed stands. Shadier and more humid interiors favour a luxuriant bryophyte flora over soil, rocks and the hazel stool bases, an ‘elfin’ aspect in which broader Atlantic and some specialist oceanic species are especially striking. The lichen flora is also particularly indicative of venerable stands with more light-demanding Graphidion species typical of smoother bark in less shady situations, Lobarion species on rougher bark and in shadier stands, both contingents including some internationally rare taxa. Hazel is ectomycorrhizal and a number of fungi can add to the floristic richness of the scrub.

The habitat described above occurs in Ireland and the United Kingdom, where it is found in locations where wind and shallow soils prevent the growth of trees. However, also in Central Europe permanent hazel scrub is found, in places where soil conditions prevent succession towards forest, for example on steep hillsides. Here also the scrub is in most cases growing on limestone, but occasionally also on other soil types. In this more continental region the herb layer consists of dry grassland and forest edge species, like Epipactis atrorubens, Campanula persicifolia, Brachypodium pinnatum and Melampyrum nemorosum. Such scrub communities are classified in the alliance Berberidion vulgaris.

Indicators of good quality:

• Presence of at least some continuous cover of healthy multi-stemmed hazel bushes without any overtopping tree canopy
• Diverse herb layer, often with complex mosaics over uneven topography
• Rich and diverse cryptogam flora
• Grazing and browsing at moderate levels at most
• Absence of signs of coppicing
• Absence of invading oceanic aliens e.g. Rhododendron ponticum.

Synthesis of Red List assessment

Confidence in the assessment

Pressures and threats