All information Copyright, Cranfield University © 2018

Citation: To use information from this web resource in your work, please cite this as follows:
Cranfield University 2018. The Soils Guide. Available: www.landis.org.uk. Cranfield University, UK. Last accessed 23/02/2018

0654a HAFREN

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Soil and site characteristics

Loamy permeable upland soils over rock with a wet peaty surface horizon and bleached subsurface horizon, often with thin ironpan. Some peat on higher ground. Rock and scree locally.

Geology

Palaeozoic slaty mudstone and siltstone

Cropping and Land Use

Moorland and grassland habitats, of moderate grazing value; recreation; coniferous woodland; stock rearing and dairying on improved ground.

Component soil series

Subgroup Series name Percentage WRB 2006 link
6.54 HAFREN 45% Endoskeletic Histic Stagnic Albic Podzols
6.51 HIRAETHOG 20% Placic Endoskeletic Histic Stagnic Albic Podzols
7.21 WILCOCKS 10% Dystric Histic Stagnosols

Covers 1530 km2 in England and Wales

Soilscapes Classification

16
Very acid loamy upland soils with a wet peaty surface

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0654a HAFREN

Detailed Description

This association consists mainly of soils with peaty surface horizons-stagnopodzols and stagnohumic gley soils on plateaux and steep valley sides. It covers some 1,300 kmĀ² of hill land mainly in Wales, with small areas in South West and Northern England. Hafren soils, loamy ferric stagnopodzols, are most widespread. Similar ironpan stagnopodzols belonging to the Hiraethog series are locally dominant. Wilcocks series, loamy stagnohumic gley soils in drift, and very stony (lithoskeletal) stagnopodzols are also common. Most of the soils are developed in rock debris from Palaeozoic mudstones, shales, siltstones and occasionally slates. Altitudes range from about 300 m O.D. near the west coast of Wales to more than 900 m O.D. on the Carneddau range in Snowdonia, although further inland at Radnor Forest in east Wales the soils are found only above about 500 m O.D. Ironpans occur frequently and are most common in north Wales and Radnor Forest where the Hiraethog series dominates, whereas in the larger areas of central and south Wales Hafren series (Lea 1975) is usually more common. Together these series cover about half the association. In the mountains of north and mid-Wales however, high ridges and plateaux have similar soils in which organic matter was mixed with or washed into very stony shattered rock debris by frost heave or leaching. These were described as a dark brown subsoil phase of Hiraethog series by Rudeforth (1970). Stone stripes and polygons are found in some of these places (Ball and Goodier 1970). Cliffs, rock fields and scree are also features of this more rugged country. Cliffs like those at Graig Goch have an overriding influence on the use and management of the land despite their limited extent. Around Machynlleth and Corris the soils are developed on slaty rocks metamorphosed by the Cader Idris igneous activity. Shallow humic rankers, Skiddaw and Revidge series , are frequent, especially in north and mid-Wales, where there are narrow rocky ridges. Basins, valleys and flushes have stagnohumic gley soils of the Wilcocks, Mynydd and Rhondda series, and also peat soils of the Crowdy and Floriston series). Winter Hill soils, fibrous peats, are included on some high plateaux. On valley sides at lower altitudes brown podzolic soils are frequent and include the Parc and Manod series. In the Preseli hills, igneous intrusions give rise to local occurrences of Bangor and Preseli series. The climate is cold and wet. Low summer temperature is the main influence on the development of stagnopodzols as distinct from brown podzolic soils on similar slopes and under similar rainfall. The accumulated temperatures range from about 800 to 1,500 day degrees centigrade and moisture deficits are generally less than 80 mm. Western districts have cooler summers and milder winters than in the east where the seasonal range of temperatures is greater.

On unreclaimed central parts of Exmoor, Hafren, and Hiraethog soils with ironpan, are accompanied by stagnohumic gley soils of the Wilcocks and shallower Mynydd series. On slopes and the drier fringes of Exmoor the peaty topsoils become thinner and some are humose rather than peaty. Here too there are fewer gley soils. On enclosed and cultivated land, particularly in Exmoor Forest, the once peaty surface horizons have become humose. In Cornwall also, on St Breock Downs and close to the St Austell granite, most topsoils are humose rather than peaty. Where repeated cultivation has ruptured the ironpan and has reduced organic matter in the topsoil, well drained Manod soils are found. Scattered Wilcocks and Mynydd soils also occur, with Cegin soils more common on long-cultivated land. Small depressions, basins and flushes have peaty soils of the Crowdy and Freni series.

The association occurs mainly in the Howgill Fells but is also at Black Combe and near Loweswater, Cumbria, and near Ravens Knowe, at the Scottish border. The climate is cold and wet. Low summer temperature is mainly responsible for the development of stagnopodzols rather than the brown podzolic soils found on similar slopes under similar rainfall elsewhere. The accumulated temperatures range from about 800 to 1500 day degrees centigrade. Western districts have cooler summers and milder winters than in the east, where the seasonal range of temperatures is greater.

Soil Water Regime

The water regime of these soils is complicated by the presence of the contrasting horizons. Water is held in the surface horizons of Hafren and Hiraethog soils, the peat acting as a sponge so that they are seasonally waterlogged even though the subsoils drain freely (Wetness Class III or IV). Where strongly formed, the ironpan also impedes water movement. Wilcocks series, in slowly permeable thick drift on the lower ground, is naturally wetter (Wetness Class V). Rainwater passes rapidly into streams and rivers when the upper horizons are already saturated, particularly in winter.

Cropping and Land Use

Sheep grazing and forestry are the main uses of this land because of the wet peaty topsoils, steep slopes and climate. Much of the land is unenclosed, under semi-natural vegetation of moderate grazing value, mainly Nardus, with less valuable heather moor where grazing is light. A proportion of heather (Calluna vulgaris) is useful, however, as it is the only source of winter grazing. Wetter parts of the association on peats and stagnohumic gley soils provide poor grazing of heather moor, blanket bog communities, or Molinia, while narrow flushes and valley bottoms are dominated by bog-mosses and rushes. With adequate machinery, improvement is possible in many places, especially on the stagnopodzols where slope and soil pattern allow. Techniques developed on these soils at Pwllpeiran Experimental Husbandry Farm involve liming, flail mowing, shallow rotavation and seeding with cultivated grasses and wild white clover. This is followed by controlled grazing by sheep and cattle to curb regrowth of native species, and a programme of fertilizer application to maintain the new sward. Much of the land has been improved using these or similar techniques, but some is too far from roads and farm buildings for such methods to be feasible at present. Some of the lower parts have bent-fescue grassland with better grazing value than the more common Nardus grasslands. Some 16 per cent of the association is under coniferous woodland, mostly Forestry Commission plantations. Before planting, wide deep furrows are drawn using specially adapted ploughs, then seedlings are planted on the upturned ridge of soil, thus keeping the young roots adequately aerated. Sitka spruce is best suited to the climate and soil, and yields well but Lodgepole pine competes better with heath vegetation and is grown above 600 in O.D. Some larch is grown on lower ground. In exposed places the problem of windthrow is exacerbated where there are waterlogged or shallow soils which prevent deep rooting. Crags and screes remain unplanted. Roads built for forestry also allow farmers access to remote land. The semi-natural vegetation provides valuable refuges for native plants and animals. As agriculture advances, heather moors are becoming increasingly rare on an international scale, and despite low productivity they have a distinctive flora and fauna. Some places are of special interest for their birds and insects, notably part of the Cader Idris National Nature Reserve, and the association includes several designated Sites of Special Scientific Interest like those on the Berwyn hills. Much of this land and the neighbouring Crowdy or Winter Hill associations, is on water-gathering grounds of reservoirs. The soils do not absorb much winter rainwater after the peaty surface layers have become saturated, so flash-floods can occur on lower land soon after heavy rain. The association provides relatively dry soils for footpaths. Cader Idris is particularly popular with walkers and campers, and local Outward Bound schools use it regularly. Many of the forest walks and nature trails laid out by the Forestry Commission pass through areas of the Hafren association.

Much of Exmoor Forest has small patches only of wet gley soils and was reclaimed in the early nineteenth century. It is now in permanent pasture used for sheep and cattle. Within the Exmoor National Park many areas are conserved as semi-natural vegetation which has a low grazing value. On high ground to the west of Simonsbath there is moist atlantic heather moor, mostly of ling and purple moor-grass. To the south-east, around Withypool, dry heather moor provides some grazing for outwintering stock. In Cornwall much of this land has been reclaimed by subsoiling to permanent or ley grassland used for dairying and stockrearing. A little unimproved land remains north of Roche, where the moist atlantic heather moor is one of the few surviving fragments of semi-natural vegetation in the county.

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0654a HAFREN

Typical Landscapes

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All information Copyright, Cranfield University © 2018

Citation: To use information from this web resource in your work, please cite this as follows:
Cranfield University 2018. The Soils Guide. Available: www.landis.org.uk. Cranfield University, UK. Last accessed 23/02/2018