Semi-natural Deciduous Woodland

Broadleaved, deciduous woodland is the successional climax ecosystem in most of the British Isles and pollen analysis informs us that it dominated the entire landscape of lowland Britain in pre-historic times. However, successive cultures and civilisations through the ages removed most of this so that today less than 10% of Britain's land is covered by deciduous woodland. In Wales semi-natural woodland occupies about 4% of the land surface, which is roughly half of the amount covered by plantation forests. However woodland cover is not even in Wales, or the rest of the country. There are regions where woodland cover is geater than the national average and this is particularly true for the administrative county of Neath Port Talbot in West Glamorgan where semi-natural broadleaved woodland occupies 20% of the land surface.

There are a number of distinct semi-natural deciduous woodland types in West Glamorgan. Some such as the Gower Ash Woodlands have developed on limestone. In contrast, those that predominate in the South Wales Coalfield, e.g. in Neath Port Talbot, have formed on acidic and often podsolic soils of the valley slopes. Atlantic ravine woodlands (Celtic Rainforest) are found in some of the valleys of West Glamorgan such as the Melincwrt Valley and in the waterfall valleys along the headstreams of the River Neath. Another woodland type can be found on the more mineral-rich, valley-bottom, alluvial soils that have developed along the main river systems such as the Neath, Afan and upper Tawe. These are referred to here as riparian corridor woodlands. Where soils are permanently wet or marshy, particularly where there is fenland, distinctive wet alder woodland has developed. These woodland are often called alder carr.

Gower Ash Woodland

The Gower Ash Woods comprise a designated Special Area of Conservation (SAC) being one of the largest Tilio-Acerion forests in Wales. The SAC is made up of six Sites of Special Scientific Interest (SSSI), Bishop's Wood, Parkmill Woodlands (Park Woods) and Llethrid Valley, Pwll Du Head and Bishopton Valley, Pennard Valley and Nicholaston Woods and Oxwhich Bay. The occurrence of Tilio-Acerion in Gower is of particular biogeographical interest because it represents the western extreme of this ecosystem's range in Britain. These woodlands have developed on a bedrock of Carboniferous Limestone which in some places is close to the surface beneath comparatively thin soils. Limestone outcops as well as caves, scattered limestone rocks and boulders are common in the karstic landscape of these wooded valleys where water courses often flow underground. These woodlands have been managed for centuries and some contain(ed) important archaeological relics in their caves and the remains of neolithic burial structures, e.g. Park Woods. Some like Park Woods were also managed for coppicing on much larger scales in the past, particularly after the Norman conquest and through the Middle Ages to modern times. Old, coppiced compartments full of Hazel (Coryllus avellana) can still be identified in places. The main trees in these woods are Ash (Fraxinus excelsior), Sycamore (Acer pseudoplatinus), Pedunculate Oak (Quercus robur), Small-leaved Lime (Tilia cordata), Wych Elm (Ulmus glabra) and Field Maple (Acer campestre) while Hazel, Dogwood (Cornus sanguinea) and Spindle (Euonymus europaeus) are important component shrubs. 

Gower's limestone woodlands support a dense and colourful, vernal herb layer with large amounts of Ramsons (Allium ursinum), Bluebell (Hyacynthoides non-scripta), Wood Anemone (Anemone nemorosa) and Dog's Mercury (Mercurialis perennis) while Soft Shield-fern (Polystichum setiferum) and Hart's-tongue (Asplenium scolopendrium) are often abundant. Other significant species here include Wood Spurge (Euphorbia amygdaloides), Early Dog-violet (Viola reichenbachiana), Sanicle (Sanicula europaea), Early Purple-orchid (Orchis mascula), Moschatel (Adoxa moschatelina), Primrose (Primula vulgaris) and Herb Paris (Paris quadrifolia). Some of these species, such as Wood Spurge, Early Dog-violet, Early Purple-orchid, Moschatel and Herb Paris are confined to Gower woodlands in West Glamorgan and do not occur in the extensive broadleaved woodland on the South Wales Coalfield in Neath Port Talbot. Less common but notable species are Purple Gromwell (Lithospermum purpureocaeruleum),  Stinking Hellebore (Helleborus foetidus) and Bitvher's Broom (Ruscus aculeatus), all of which occur in Crawley Woods, and the small population of Spurge Laurel (Daphne laureola) which is found in the Llethrid Valley. Also notable is a sigificant and locally common population of Thin-spiked Wood Sedge (Carex strigosa) that occurs in Park Woods. 

Gower Ash Woods also support some significant calcicole bryophyte assemblages. Plasteurynchium striatulum, a scarce species in Wales, is locally common on rocks and boulders in Park Woods and the Bishopston Valley while Anomodon viticulosus and Neckera crispa are sometimes prominently draped from vertical outcrops. Some of the large limestone boulders in the Bishopston Valley support the almost black colonies of the liverwort, Marchesinia mackaii while Neckera complanata is a common epiphyte on tree trunks and Isothecium alopecuroides, which is uncommon in West Glamorgan outside Gower, occurs at their bases.

Sessile-oak Woodland in the Valleys and West Glamorgan's Atlantic Rainforest

The often steep-sided valleys of the Neath and Afan Valleys support significant amounts of sessile-oak woodland on acidic soils often formed on a bedrock of Pennant Sandstone. Sessile-oak (Quercus petraea) dominates the tree layer with various amounts of Rowan (Sorbus aucuparia), birches (Betula pubescens and Betula pendula) and Holly. Hazel is usually scarce on the steeper slopes but may be abundant on the richer soils near the valley bases and on the margins. The ground flora of these woodlands are often quite grassy with species such as Common Bent (Agrostis capillaris),  Creeping Soft-grass (Holcus mollis) and Wavy Hair-grass (Deschampsia flexuosa) and there are a few where Purple Moor-grass (Molinia caerulea) dominates the ground flora. Others may have a dominant, ericaceous,  sub-shrub layer with Bilberry (Vaccinium myrtillus) and Heather (Calluna vulgaris) and many are quite fern-rich with lots of Hard Fern (Blechnum spicant), Broad Buckler-fern (Drypoteris dilatata), Scaly Male-fern (Dryopteris affinis), Lady Fern (Athyrium filix-femina) and Bracken (Pteridium aquilinum). Bluebell, Wood Sorrel (Oxalis acetosella) and Common Dog-violet (Viola riviniana) provide most of the spring colour in these woods, with rarer appearances of Wood Anemone, but these acidic woodlands do not produce the spectacular ground-flora displays in spring that are common in the limestone woodlands of Gower. The Quercus patraea-Betula pubescens-Oxalis acetosella community (W11 in the NVC classification) is frequently represented in the lower valleys while those in the more humid ravine woodlands of the uplands conform more to Quercus petraea-Betula pubescens-Dicranum majus variant (W17). This a woodland community with a more bryophyte-rich ground flora. Mosses such as Dicranum majus, Polytrichum formosum, Plagiothecium undulatum and Rhytidiadelphus loreus predominate with Hookeria lucens in wetter areas and, occasionally, Sphagnum quinquefarium on the well-drained slopes. Decaying logs are often rich in liverworts such as Blepharostoma trichophyllum, Cephalozia curvifolia, Odontoschisma denudata and Riccardia palmata.

In the humid ravines of the headstream valleys of the Nedd Fechan and Pyrddin rivers, especially in the vicinity of waterfalls, there are some important Atlantic (including Hyperoceanic) bryophyte assemblages with species such as Aphanolejeunea microscopica, Frullania tamarisci, Jubula hutchinsiae, Lejeunea patens, Plagiochila spinulosa, Plagiochila bifaria and Breutelia chrysocoma. The occurrence of some northern boreal species close to their British southern limits here, such as Odontoschisma denudata, Blindia acuta and Anoectangium aestivum, is also interesting. Other northern species such as Beech Fern (Phegopteris connectilis), Oak Fern (Gymnocarpium dryopteris), Stone Bramble (Rubus saxatilis), Marsh Hawk's-beard (Crepis pauldosa) and Wood Fescue (Drymochloa sylvatica) are also found in these places.

Riparian Corridor Woodlands

While the sessile-oak woodlands on the steep valley slopes in the South Wales Coalfield are relatively poor in colourful vernal herbs, the woodlands that occur in the valley bases are more comparable to the biodiverse Gower ashwoods. The relatively well drained, alluvial soils that predominate here are more mineral-rich and more base-rich than the posolic soils on the valley slopes and there is little dounbt that they once supported more widespread broadleaved forests. Today, these woodlands form a semi-natural deciduous woodland corridor along the Neath, Afan and Tawe rivers. They are particularly well developed and diverse in the Vale of Neath and in the upper Tawe valley between Pontardawe and Ystalyfera. Wych Elm is one of the most conspicuous trees in these riparian woodland along with Ash, Sycamore, Small-leaved Lime, willows (Salix spp.) and Alder (Alnus glutinosa). Oaks are also represented but they are not dominant species in these communities. The ground flora is often dominated by Ramsons but Wood Anemone, Dog's Mercury, Primrose, Sanicle, Woodruff, Pignut (Conopodium majus), Cow Parsley (Anthriscus syvestris), are also common. Hard Shield-fern (Polystichum aculeatum) and Soft Shield-fern are frequent here along with Great Wood-rush (Luzula sylvatica). Some of the more conspicuous bryophytes in the ground flora include Plagiochila porelloides, Plagiochila aslenioides, Cirriphyllum piliferum and Rhytidiadelphus triquetrus and the more base-rich, sandy riverside soils occasionally support populations of Mnium marginatum. In many spots along the wood-shaded banks of River Neath between Aberdulais and Glyn Neath there are some significant populations of Meadow Saxifrage (Saxifraga granulata), a scarce species in Wales.

Wet Alder-Willow Woodland (Alder Carr)

In West Glamorgan, these woodlands are best developed in lowland fens and marshes such as Oxwhich Marsh, Crymlyn Fen and Morfa Fen as well as various areas on Crymlyn Burrows and along the Neath and Tennnat canals. They are dominated by Alder with variable amounts of willows such as Grey Willow (Salix cenerea) and Goat Willow (Salix caprea). The permanently wet ground, which is often flooded, supports a flora with species such as Greater Tussock-sedge (Carex paniculata), Remote Sedge (Carex remota), Water Horsetail (Equisetum fluviatile), Marsh Marigold (Caltha palustris), Gypsywort (Lycopus europaeus), Common Skullcap (Scutellaria galericulata), Yellow Loosestrife (Lysimachia vulgaris), Yellow Iris (Iris pseudoplatinus), Opposite-leaved Golden-saxifrage (Chrysosplenium oppositifolium), Lady Fern and rarely, Marsh Fern (Thelypteris palustris). The most conspicuous bryophytes in this habitat are Pellia epiphylla, Brachythecium rivulare, Calliergon cordifolium, Kindbergia praelonga, Plagiomnium elatum and Plagiomnium undulatum. Trees are often covered in common epiphytic lichens and bryophytes.

Wet alder-willow woodlands have a diverse assemblage of macroscopic fungi. Gyrodon lividus is a nationally uncommon bolete associated with Alder which has been found in the wet carr woodlands of Oxwich marsh and also in Morfa Fen. Several Naucoria species are also associated with this habitat including Naucoria amarescens (with willows), Naucoria striatula and the ubiquitous Naucoria escharioides (both with Alder).