Soil Associations

0313c CRWBIN

Soil and site characteristics

Very shallow and shallow well drained loamy soils over limestone, often on steep slopes. Limestone pavement and other rock exposures common.

Geology

Carboniferous limestone

Cropping and Land Use

Stock rearing on herb-rich grassland habitats of good grazing value; recreation; some arable In lowlands.

Component soil series

Subgroup	Series name	Percentage	WRB 2006 link
3.13	CRWBIN	50%	Eutric Leptosols
5.41	MALHAM	30%	Eutric Endoleptic Cambisols
5.41	WALTHAM	10%	Eutric Endoleptic Cambisols

Covers 432 km² in England and Wales

Soilscapes Classification

7	Freely draining slightly acid but base-rich soils

0313c CRWBIN

Detailed Description

The Crwbin association consists mainly of loamy brown rankers of the Crwbin series associated with typical brown earths over limestone belonging to Malham and Waltham series. It is found on limestone mainly of Carboniferous age in the South West, Wales, Northern England and the Peak District. The fine earth of almost all constituent profiles is decalcified although some calcareous profiles, Marian series remain. Bare rock in the form of limestone pavements and small crags is common and many of the soils are stony. The pattern and proportions of the soils differ according to terrain. On level ground the Ma!ham and Waltham series occur in drift-filled depressions in the underlying rock, whereas on sloping land they are commonly found in Head on footslopes and associated with screes. Since there is little weathered residue from the limestone, most profiles have a large drift component. The silty fine earth of Malham soils is of windblown origin, while the fine loamy Waltham series occurs in glacial drift containing sandstone. Where the drift source is Devonian or Triassic rock the soils are reddish. Clayey brown rankers (Torbryan series, Clayden and Hollis 1984) occur as minor inclusions. The Wetton series, a humic ranker similar to the Marian series but non-calcareous, is also found.

South West England, Wales, Northern England and the Peak District. The fine earth of almost all constituent profiles is decalcified although there are some humic rendzinas, Marian series. Bare rock in the form of limestone pavements and small crags is common and many soils are stony. On the Mendips of Somerset and Avon the association occupies steep hill slopes and the sides of some valleys on the plateau. Around Bristol, the soils extend over most of Broadfield Down, around Bristol airport, along the ridges north of Clevedon and between Alveston and Wickwar. West of the Severn the association is found from Chepstow, through the lower Wye valley, to Micheldean. It is also mapped over Devonian limestone between Newton Abbot and Brixham. Little of the silt-sized soil material is weathered from the underlying limestone and much is of aeolian origin. Soils formerly mapped as Lulsgate series are now classified as Crwbin series or deeper Malham series. Loamy reddish typical brown earths derived from Triassic Conglomerates belong to the Wrington series. Clayey brown rankers, Torbryan series, are only in Devon on steep rocky slopes, with the deeper silty soils in dry valleys and on flat ground.

The association occupies limestone outcrops in Cumbria, around Morecambe Bay and near Crosby Ravensworth; also in Ribblesdale, North Yorkshire. The pattern and proportions of the soils differ according to terrain. On level ground the Malham and Waltham series occur in drift-filled depressions in the underlying rock, whereas on sloping land they are commonly found in Head on footslopes. Since there is little weathered residue from the limestone, most profiles have a large drift component. The silty fine earth of Malham profiles is of windblown origin, while the fine loamy Waltham series occurs in glacial drift containing sandstone. Where the drift source is Triassic rock the soils are reddish Wrington serie. Torbryan, Wetton and Marian series occur as minor inclusions. In some areas, generally above 300 m O.D., the Lonsdale series has been recognized and included as a minor component.

Soil Water Regime

Most of the soils are permeable and well drained (Wetness Class I) so they readily absorb excess winter rain.

Cropping and Land Use

Most of the land is used for rough grazing and the bent-fescue grassland gives valuable grazing, with little poaching risk where steep slopes and rock outcrops preclude cultivation or intensive grassland management. Scrub and woodland are fairly extensive, some such as Oxwich Wood on the Gower cliffs of south Wales being nature reserves because of their rich herb flora. Droughtiness is a serious limitation but where soil depth, stoniness and gradient permit there is some improved pasture and arable cultivation, the latter notably on the footslopes of the Gower cliffs where vegetables are grown. Crwbin soils are too shallow for commercial afforestation and the limestone substratum produces chlorosis and inhibits growth in most conifers.

In the South West steep slopes and rock outcrops generally preclude cultivation or intensive grassland management so most of the land is used for rough grazing. Droughtiness is a serious limitation but where soil depth, stoniness and gradient permit there is some improved pasture and arable cultivation, the latter notably on the plateau around Wickwar in Avon where cereals are grown. Scattered woodland is a feature of the association, particularly on steeper slopes. The base-rich nature of the soils and shallowness to limestone mean that calcicole species dominate the semi-natural unmanaged deciduous woodlands. Here oak (Quercus spp.), ash (Fraxinus spp.), small leaved lime (Tilia cordata), field maple (Acer campestre), wych elm (Ulmus glabra) and sycamore (Acer pseudoplatanus) are all common and each may dominate a small locality, for example small leaved lime near Weston-super-Mare. Whitebeam (Sorbus aria) and yew (Taxus baccata) also occur locally, particularly the former in Leigh Woods and the Avon Gorge near Bristol. In south Devon the rich calcicole vegetation on these soils contrasts strikingly with the more usual communities on soils of low base status. There are nature reserves locally, as at Rodney Stoke on the Mendips. Managed woodland includes a range of species but conifers perform poorly, and only Western red cedar (Thuja plicata) and the larches (Larix spp.) yield satisfactorily. Beech (Fagus sylvatica) does well. Rock outcrops and steep slopes can make harvesting of timber difficult, often requiring special equipment.

0313c CRWBIN

Distribution Map

Note that the yellow shading represents a buffer to highlight the location of very small areas of the association.

Keys to component soil series

Northern Region

Wales

Typical Landscapes

South Western Region

Midlands

Northern Region

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Citation: To use information from this web resource in your work, please cite this as follows:
Cranfield University 2024. The Soils Guide. Available: www.landis.org.uk. Cranfield University, UK. Last accessed 19/04/2024