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Special Areas of Conservation

9180 Tilio-Acerion forests of slopes, screes and ravines


Description and ecological characteristics

Tilio-Acerion ravine forests are woods of ash Fraxinus excelsior, wych elm Ulmus glabra and lime (mainly small-leaved lime Tilia cordata but more rarely large-leaved lime T. platyphyllos). Introduced sycamore Acer pseudoplatanus is often present and is a common part of the community in mainland Europe, where it is native. The habitat type typically occurs on nutrient-rich soils that often accumulate in the shady micro-climates towards the bases of slopes and ravines. Therefore it is found on calcareous substrates associated with coarse scree, cliffs, steep rocky slopes and ravines, where inaccessibility has reduced human impact. It often occurs as a series of scattered patches grading into other types of woodland on level valley floors and on slopes above, or as narrow strips along stream-sides. More extensive stands occur on limestone and other base-rich rocks.

This habitat type is ecologically variable, particularly with respect to the dominant tree species. To the north and west, ash and wych elm assume increasing importance in the canopy, and lime may be completely absent. Floristic differences due to variations in slope, aspect and nature of the substrate add to the diversity of the habitat. The ground flora can be very varied, but the following elements are usually present: fern banks (particularly hart’s-tongue Phyllitis scolopendrium, soft shield-fern Polystichum setiferum and buckler-ferns Dryopteris spp.); stands of ramsons Allium ursinum in the moister zones; dog’s mercury Mercurialis perennis and enchanter’s-nightshade Circaea spp. on drier but still base-rich soils; wood avens Geum urbanum, and natural ‘disturbance communities’ comprising common nettle Urtica dioica, herb-Robert Geranium robertianum and cleavers Galium aparine associated with scree and cliff-bases. A wide range of other basiphilous herbs and grasses may occur within these stands.

The main NVC types conforming to Tilio-Acerion forests are the ‘western’ forms (sub-communities d-g) of W8 Fraxinus excelsior – Acer campestre-Mercurialis perennis woodland, and the equivalent north-western community W9 Fraxinus excelsior – Sorbus aucuparia – Mercurialis perennis woodland.

North of the central belt in Scotland, and in upland areas generally, base-rich conditions tend to become more restricted in extent; birch Betula spp. and oak Quercus spp. assume greater abundance in the canopy, and species typical of more acidic communities are often found in a close mosaic with more basiphilous indicators. However, the type is still recognisable in, for example, the hazel Corylus avellana stands of the north-west coast of Scotland rich in lichens and higher plants.

Tilio-Acerion forests provide a habitat for a number of uncommon vascular plants, including, dark-red helleborine Epipactis atrorubens, violet helleborine Epipactis purpurata, wood fescue Festuca altissima, purple gromwell Lithospermum purpureocaeruleum and herb-Paris Paris quadrifolia. Many sites support notable bryophytes, in particular calcicoles associated with base-rich rock outcrops and (in western stands) Atlantic species. Some localities have important assemblages of epiphytic lichens.

Distribution of SACs/SCIs/cSACs with habitat 9180 Tilio-Acerion forests of slopes, screes and ravines. Click image for enlarged map.

European status and distribution

Tilio-Acerion has its centre of distribution in continental Europe, but is widespread from Scandinavia through to the Pyrenees and into Italy. Typically it occurs in association with base-rich rocks in the steep-sided immature river valleys of the colline, sub-montane and high mountain belts across Europe.

UK status and distribution

Tilio-Acerion forests are not extensive in the UK, although fragmentary stands are widespread. The UK stands of Tilio-Acerion forests closest in composition to the stands in mainland Europe tend to occur on the upland-lowland boundary in England and on the Welsh border. Fragmentary outlying stands of similar composition occur in chalk combes in south-east England, while related stands occur also in the north and west.

Click here view UK distribution of this species

Site accounts

  • Alyn Valley Woods/ Coedwigoedd Dyffryn Alun East Wales, West Wales and The Valleys
    Alyn Valley Woods holds one of the largest continuous areas of Tilio-Acerion forest in Wales, and is one of three sites selected to represent the geographic range and variation of the habitat on the Carboniferous limestone of north Wales. The canopy is predominantly of ash Fraxinus excelsior and sycamore Acer pseudoplatanus, with an understorey and ground flora typical of Tilio-Acerion in the UK. Rare or distinctive species include herb Paris Paris quadrifolia, stinking hellebore Helleborus foetidus, green-flowered helleborine Epipactis phyllanthes, toothwort Lathraea squamaria and spurge laurel Daphne laureola. The site also holds the region’s largest population of wayfaring tree Viburnum lantana.
  • Avon Gorge Woodlands Gloucestershire, Wiltshire and Bristol/Bath area
    Avon Gorge is representative of Tilio-Acerion forests in south-west England on the limestone cliffs and screes of a large river gorge. It is important because of the high concentration of small-leaved lime Tilia cordata, compared with other sites in the region, the presence of rare whitebeams Sorbus spp., including two unique to the Avon Gorge (S. bristoliensis and S. wilmottiana), and other uncommon plants, such as green hellebore Helleborus viridis. Other characteristic species include soft shield-fern Polystichum setiferum and hart’s-tongue Phyllitis scolopendrium. Species-rich transitions to scrub and grasslands are associated with the woodland. Small groves of yew Taxus baccata also occur on some of the stonier situations.
  • Borders Woods Eastern Scotland
    This complex of gorge woodland sites in south-east Scotland contains very good examples of Tilio-Acerion forests. The woodlands are of mixed-age, coppiced ash Fraxinus excelsior and wych elm Ulmus glabra with varied structure and a diverse field-layer rich in calcicolous and nitrophilous plant species. The woodlands have developed on steep, flushed slopes with open seepages and base-rich soils along tributary streams of the River Tweed. The plant communities have affinities with examples of the habitat in lowland England.
  • Clyde Valley Woods South Western Scotland
    Clyde Valley Woods in southern Scotland represents the most extensive complex of woodland gorges with Tilio-Acerion forests in Scotland. Although, like all Scottish sites, Clyde Valley Woods is beyond the northern distribution limit of lime Tilia spp. it possesses otherwise characteristic features of the Tilio-Acerion. Ground flora typical of the Tilio-Acerion is found in these woods, with some southern species such as herb-Paris Paris quadrifolia and pendulous sedge Carex pendula also present.
  • Coed Cwm Einion West Wales and The Valleys
    Coed Cwm Einion is an example of Tilio-Acerion woodland in the extreme west of the habitat’s range. This small but unusual wood extends up a steep gorge, and has a canopy with much ash Fraxinus excelsior and good representation of small-leaved lime Tilia cordata. The ground flora is diverse, and includes an exceptional Atlantic bryophyte and fern flora. Notable species include Tunbridge filmy-fern Hymenophyllum tunbrigense, hay-scented buckler-fern Dryopteris aemula, the nationally scarce liverwort Plagiochila atlantica, and the Red Data Book lichen Parmelia robusta.
  • Coedwigoedd Dyffryn Elwy/ Elwy Valley Woods West Wales and The Valleys
    Elwy Valley Woods is one of three sites selected to represent Tilio-Acerion forest across its geographic range on the Carboniferous limestone of north Wales, and is an example of the habitat with an outstanding lower-plant flora. The canopy is quite varied: ash Fraxinus excelsior is the commonest tree, but there is also occasional small-leaved lime Tilia cordata and wild service-tree Sorbus torminalis. There is a rich, calcicolous understorey and ground flora, and rare bryophytes include Bryum canariense, Cololejeunea rossettiana, Plagiochila britannica, Platydictya confervoides and Isothecium striatulum. The woods have developed along steep valley-sides and ravines that are also important for their cave systems and Pleistocene fossil mammal assemblages.
  • Coedwigoedd Penrhyn Creuddyn/ Creuddyn Peninsula Woods West Wales and The Valleys
    Creuddyn Peninsula Woods has developed on a series of craggy Carboniferous limestone hills, and is a large example of Tilio-Acerion forest near its western extreme at this latitude in the UK. The site is one of three selected to represent the geographic range and variation of this habitat across the Carboniferous limestone of north Wales. The canopy is primarily of ash Fraxinus excelsior and sycamore Acer pseudoplatanus, with a calcicolous understorey and ground flora. Characteristic species include dog’s mercury Mercurialis perennis, hart’s-tongue Phyllitis scolopendrium and spurge laurel Daphne laureola. Yew Taxus baccata dominates locally, and there are gradations to oak Quercus petraea woodland. In places there are mosaics with rich calcareous grassland containing many rare species.
  • Craighall Gorge Eastern Scotland
    With Keltneyburn, Craighall Gorge is one of two sites selected to represent the central-eastern range of Tilio-Acerion forest within Scotland. It is one of a series of wooded gorges in the region cut into Old Red Sandstone. There is a well-developed sub-montane basicolous bryoflora, particularly on the conglomerate cliffs, and a lichen flora which includes old woodland indicator species, and one semi-aquatic species occurring in the River Ericht, ear-lobed dog lichen Peltigera lepidophora, for which this site is the only known British station. On the steep slopes of the gorge there is a considerable amount of ash Fraxinus excelsior with some wych elm Ulmus glabra. The ground flora is extremely species-rich with a large number of higher plants of restricted distribution, including the nationally rare whorled Solomon’s seal Polygonatum verticillatum. The dead-wood resource is outstanding, as there has been little management intervention.
  • Downton Gorge Herefordshire, Worcestershire and Warwickshire
    Downton Gorge is an example of Tilio-Acerion forests in a narrow ravine with a distinctive microclimate and a variety of slopes and aspects. Both small-leaved lime Tilia cordata and large-leaved lime T. platyphyllos occur, together with ash Fraxinus excelsior and elm Ulmus spp. The ground flora includes wood fescue Festuca altissima and violet helleborine Epipactis purpurata. The gorge cliffs are rich in ferns, reflecting the humidity of the site, with a wide range of species recorded.
  • East Hampshire Hangers Hampshire and Isle of Wight
    East Hampshire Hangers, with Rook Clift, represents an unusual occurrence of Tilio-Acerion forests in the south of England. It has areas of small-leaved lime Tilia cordata on the steepest parts of the Upper Greensand scarp, associated with low sandstone cliffs and scree slopes, which are locally calcareous. The bryophyte flora is richer than on the chalk examples and includes several species that are rare in the lowlands, such as Campylostelium saxicola, which has its strongest population in England here. The site is ecologically similar to sites selected in the Welsh Borders, despite its geographic location.
  • Gower Ash Woods/ Coedydd Ynn Gŵyr East Wales
    Gower Ash Woods comprises one of the most extensive areas of Tilio-Acerion forest in Wales and is near the western extreme of the habitat’s range in the UK. The woods are formed along a series of largely inter-linked valleys and ravines cut into Carboniferous limestone, and also on coastal slopes and cliffs with unique transitions through scrub to sand dunes, freshwater marsh and saltmarsh. The woods have a great diversity of trees and shrubs, including ash Fraxinus excelsior, sycamore Acer pseudoplatanus, pedunculate oak Quercus robur, small-leaved lime Tilia cordata, field-maple Acer campestre, dogwood Cornus sanguinea and spindle Euonymus europaeus. The ground flora is rich, with dramatic vernal displays of ramsons Allium ursinum and bluebell Hyacinthoides non-scripta and characteristic species such as hart’s-tongue Phyllitis scolopendrium. Rare species include purple gromwell Lithospermum purpureocaeruleum and butcher’s-broom Ruscus aculeatus.
  • Helbeck and Swindale Woods Cumbria
    The Tilio-Acerion woods here have developed over limestone, with crags, blocks and fine scree showing through in parts. In the Swindale section there is a steep-sided gorge with cliffs up to 30 m high. The wood is predominantly ash Fraxinus excelsior with some elm Ulmus sp. and has a rich ground flora, including the helleborines Cephalanthera longifolia, Epipactis atrorubens and E. helleborine, and wood barley Hordelymus europaeus.
  • Keltneyburn Eastern Scotland
    Keltneyburn complements Craighall Gorge as a representative of Tilio-Acerion forests in eastern/central Scotland. Gorge woodland here occurs on Dalradian schists, and the ground flora of the woodland is species-rich with a large number of higher plant species of restricted distribution, including the nationally rare whorled Solomon’s seal Polygonatum verticillatum. There is a species-rich bryoflora including several local basicolous species.
  • Kippenrait Glen Eastern Scotland
    This gorge woodland represents Tilio-Acerion forest in central Scotland. Kippenrait Glen consists mainly of base-rich mixed valley woodland of ancient/long-established origin and is the largest woodland of this type in Stirling district. The wood is relatively undisturbed and has an extremely high diversity of woodland plant species. There are extensive stands dominated by ash Fraxinus excelsior and elm Ulmus spp., and the rich, characteristic ground flora includes dog’s mercury Mercurialis perennis, sanicle Sanicula europaea, enchanter’s nightshade Circaea lutetiana and the locally rare herb-Paris Paris quadrifolia.
  • Loch Etive Woods Highlands and Islands
    Some good examples of Tilio-Acerion forest occur in the deeply-incised rocky gorges associated with Glen Nant and in the nearby Coille Leitire. These sites are representative of the habitat type in western Scotland, and comprise stands of ash Fraxinus excelsior woodland with a hazel Corylus avellana understorey and a rich field layer of tall herbs and woodland grasses on base-rich soils characteristic of the habitat.
  • Lower Findhorn Woods Highlands and Islands
    The Lower Findhorn Woods represent Tilio-Acerion forest in the north-eastern part of its range in the UK. The River Findhorn flows through a deep gorge, the sides of which are cloaked in ancient semi-natural woodland, and there are some very good stands of the habitat scattered along the 7 km length of this site, wherever suitable topographic and soil conditions occur. The ground flora is species-rich with good floristic assemblages and several locally rare species, and the outstanding epiphytic lichen flora represents a highly continental type similar to that of dry mixed oak forests in southern Scandinavia.
  • Mendip Woodlands Dorset and Somerset
    Mendip Woodlands in south-west England is a relatively extensive example of Tilio-Acerion forests on limestone. It is a cluster of three ash-dominated woods on Carboniferous limestone. A rich variety of other trees and shrubs are present, including elm Ulmus spp. and, locally, small-leaved lime Tilia cordata. At Ebbor Gorge elm rather than lime is mixed with ash Fraxinus excelsior in a steep-sided gorge; at both Rodney Stoke and Cheddar Wood lime and ash are found on rocky slopes with patches of deeper soil between the outcrops. Ferns characteristic of this woodland type, such as hart’s-tongue Phyllitis scolopendrium and shield-ferns Polystichum spp., are common. The site is in the centre of the range of common dormouse Muscardinus avellanarius and holds a large population of this species.
  • Morecambe Bay Pavements Cumbria, Lancashire
    Woodland within Morecambe Bay Pavements, along with the nearby Roudsea Wood, represents Tilio-Acerion forests on Carboniferous limestone in north-west England. Although close to the northern limit of lime distribution, the ash Fraxinus excelsior-dominated woodland around Morecambe Bay contains many patches of small-leaved lime Tilia cordata, which survive sometimes with elm Ulmus spp., often along outcrop edges. There is a rich assemblage of rare species, including fingered sedge Carex digitata, wood fescue Festuca altissima and mezereon Daphne mezereum. The habitat type occurs here both on 8240 Limestone pavements and on loose scree and steep slopes.
  • Morvern Woods Highlands and Islands
    The woods in this complex of predominantly coastal sites contain important stands of Tilio-Acerion forests on basalt, representing the extreme north-western end of the range of variation of the habitat in the UK. The complex contains a variety of manifestations of the habitat, ranging from low stunted hazel Corylus avellana-dominated woods at Drimnin to extensive ash Fraxinus excelsior-dominated stands on the coastal scree and gorges at Inninmore. The lichen and bryophyte flora is outstanding with many Atlantic bryophyte species recorded, and these are the richest woods in Lochaber for vascular plants.
  • Ness Woods Highlands and Islands
    This complex of sites includes one of the best and most extensive examples of a ravine woodland in Scotland at Glen Tarff; further examples occur along the north-facing shores of Loch Ness. The canopy is a mixture of alder Alnus glutinosa, ash Fraxinus excelsior and wych elm Ulmus glabra with a locally abundant hazel Corylus avellana shrub layer. The ground flora is rich in ferns, mosses and herbaceous plants, and the woods have a luxuriant epiphytic flora of lichens, liverworts and mosses with Atlantic affinities.
  • North Somerset and Mendip Bats Dorset and Somerset, Gloucestershire, Wiltshire and Bristol/Bath area
    The main block of Tilio-Acerion forest at Kings and Urchin’s Wood has developed over limestone which outcrops in parts of the site and forms a steep scarp to the south-east. Ash Fraxinus excelsior predominates in the canopy with small-leaved lime Tilia cordata, yew Taxus baccata and elm Ulmus spp., mostly formerly coppiced, but including some pollard limes. There is a rich ground flora including lily-of-the-valley Convallaria majalis, columbine Aquilegia vulgaris, angular Solomon’s-seal Polygonatum odoratum and purple gromwell Lithospermum purpureocaeruleum.
  • Peak District Dales Derbyshire and Nottinghamshire, Shropshire and Staffordshire
    Representing the north-central part of its UK range, this site in the English Midlands contains a large area of Tilio-Acerion, dominated by ash Fraxinus excelsior. Locally, sycamore Acer pseudoplatanus is abundant. The Dales provide good examples of woodland-scrub-grassland transitions, with associated rich invertebrate populations and plant communities. Among the uncommon plants present in the woods are mezereon Daphne mezereum and green hellebore Helleborus viridis, as well as whitebeams Sorbus spp. on the crags.
  • Rassal Highlands and Islands
    Rassal is unique in Scotland as the only large ash Fraxinus excelsior wood on limestone, and is important in representing Tilio-Acerion forest at the extreme north-western limit of its range. The site also encompasses the adjacent Allt Mór Gorge which contains further examples of the habitat. The wood is nationally important, particularly for its lichens, and the ground flora is species-rich with a number of plants of very restricted distribution, such as dark-red helleborine Epipactis atrorubens.
  • Rook Clift Surrey, East and West Sussex
    Rook Clift is the largest known remnant stand of Tilio-Acerion forests dominated by large-leaved lime Tilia platyphyllos in the south of England. It lies on the deeper soils towards the base of the slope and valley bottom of a small wooded combe, which gives the site its humid microclimate. The soils are rather deeper and there is less exposed rock at this site because the chalk is more readily weathered than the limestones on which many of the other sites lie. Despite this, the vegetation is otherwise typical of the habitat type, with an abundance of ferns such as hart’s-tongue Phyllitis scolopendrium and shield-fern Polystichum spp. In addition to species more common in the west of Britain, continental species such as Italian lords-and-ladies Arum italicum also occur.
  • Roudsea Wood and Mosses Cumbria
    Woodland at Roudsea, with others within the nearby Morecambe Bay Pavements, represents Tilio-Acerion forests on Carboniferous limestone in north-west England. Although close to the northern limit of lime distribution, the ash Fraxinus excelsior-dominated woodland around Morecambe Bay contains many patches of small-leaved lime Tilia cordata, which survive sometimes with elm Ulmus spp., often along outcrop edges. There is a rich assemblage of rare species, including fingered sedge Carex digitata. A notable feature of this wood is the sudden vegetation change across the boundaries between the limestone, where the Tilio-Acerion occurs, and acid peats or Silurian slates.
  • Sidmouth to West Bay Devon, Dorset and Somerset
    This site includes an area of active landslipping between Axmouth and Lyme Regis. These landslips have created, and will continue to shape, the mosaic of Tilio-Acerion, sycamore Acer pseudoplatanus woodland, mixed scrub, grassland and pioneer communities. This mosaic of habitats makes this site rich in invertebrates, especially bees and wasps, such as Ectemnius ruficornis, Andrena simillima and Nomada fulvicornis. The woodland has a hazel Corylus avellana understorey and a ground-flora dominated by ivy Hedera helix (with numerous ivy broomrape Orobanche hederae) and hart’s-tongue Phyllitis scolopendrium, with abundant dog’s mercury Mercurialis perennis and tutsan Hypericum androsaemum. The Red Data Book lichen Parmelia quercina occurs on ash Fraxinus excelsior trees.
  • Upper Nithsdale Woods South Western Scotland
    This complex of sites located on the River Nith and tributaries represents Tilio-Acerion forest in south-west Scotland. The individual sites are small, but regionally important due to the highly fragmented nature of remnant semi-natural woodland in this part of Scotland. The woods are ash Fraxinus excelsior-dominated with a dense hazel Corylus avellana understorey, and a rich herbaceous ground flora characteristic of the habitat type.
  • West Fermanagh Scarplands Northern Ireland
    West Fermanagh Scarplands represents the largest area of Tilio-Acerion forests in Northern Ireland. The limestone soils tend to be freely-draining and the canopy is generally dominated by ash Fraxinus excelsior, with hazel Corylus avellana and occasional hawthorn Crataegus monogyna, rowan Sorbus aucuparia and holly Ilex aquifolium in the understorey. Bramble Rubus fruticosus agg., stone bramble R. saxatilis and a diverse fern community form a characteristic field layer. The ground flora is species-rich and is often dominated by meadowsweet Filipendula ulmaria and wood-sorrel Oxalis acetosella, with species such as primrose Primula vulgaris, barren strawberry Potentilla sterilis, herb-robert Geranium robertianum and common dog-violet Viola riviniana. Other species that commonly occur include great wood-rush Luzula sylvatica, bluebell Hyacinthoides non-scripta, wood anemone Anemone nemorosa and ramsons Allium ursinum. Bryophytes form a dense carpet over soils and exposed rock faces and boulders. The woods are particularly rich in species that are scarce in Northern Ireland, including toothwort Lathraea squamaria, bird’s nest orchid Neottia nidus-avis, Welsh poppy Meconopsis cambrica, wood fescue Festuca altissima, thin-spiked wood sedge Carex strigosa and the lichen Lobaria pulmonaria. Epiphytic bryophytes are well-developed on tree trunks and branches throughout the woodlands, which are also important for their exceptionally rich and diverse fungal assemblage.
  • Wye Valley Woodlands/ Coetiroedd Dyffryn Gwy Gloucestershire, Wiltshire and Bristol/Bath area, Herefordshire, Worcestershire and Warwickshire, West Wales and The Valleys
    The woods of the lower Wye Valley on the border of south Wales and England form one of the most important areas for woodland conservation in the UK and provide the most extensive examples of Tilio-Acerion forest in the west of its range. A wide range of ecological variation is associated with slope, aspect and landform. The woodland occurs here as a mosaic with other types, including beech Fagus sylvatica and pedunculate oak Quercus robur stands. Uncommon trees, including large-leaved lime Tilia platyphyllos and rare whitebeams such as Sorbus porrigentiformis and S. rupicola are found here, as well as locally uncommon herbs, including wood barley Hordelymus europaeus, stinking hellebore Helleborus foetidus, narrow-leaved bitter-cress Cardamine impatiens and wood fescue Festuca altissima.

SACs where this Annex I habitat is a qualifying feature, but not a primary reason for site selection

Many designated sites are on private land: the listing of a site in these pages does not imply any right of public access.

Please note that the map shows sites where the presence of a feature is classed as ‘grade d’, but these sites are not listed. This is because ‘grade d’ indicates a non-significant presence.