Historic Landscape Characterisation

East Fforest Fawr and Mynydd-y-Glôg

THE NATURAL ENVIRONMENT

Various aspects of the natural environment of Fforest Fawr and Mynydd-y-glôg are considered in some detail in the Royal Commissions’s Mynydd Du and Fforest Fawr: The Evolution of an Upland Landscape in South Wales (1997), which are summarized here.

At the north the area rises to the summit of Fan Fawr at a height of about 734 metres above sea level, the second highest peak of Fforest Fawr after Fan Brycheiniog which lies about 14 kilometres to the west. Southwards the bleak upland gradually drops to a height of about 300 metres, dissected by the narrow, steep-sided, rejuvenated stream channels of the Afon Hepste and its tributaries, gradually merging at about 350 metres into the enclosed, lower-lying parts of Dyffryn Hepste, Cwm Cadlan and Pant Sychbant valleys which continue to fall to about 250-300 metres. To either side the land drops much more abruptly, into the more steep-sided valleys of the Mellte to the west and the Taf Fawr to the east.

The underlying solid geology of the area is varied and includes Old Red Sandstone to the north which forms the north-facing escarpment of the Brecon Beacons, to the south of which is a belt of Carboniferous limestone and Millstone Grit. During the last ice age the landscape was affected by glaciers and ice sheets, ice flowing out radially from the summit of the Beacons, deepening the pre-existing south-draining river valleys of the Mellte, Hepste and Taf Fawr and depositing glacial drift deposits within them. The resistant outcrop of Millstone Grit on Mynydd-y-glog deflected the passage of the ice to the east and west, creating Pant Sychbant, a dry valley which cuts across the landscape at a different angle to the river valleys. A distinctive characteristic of the Carboniferous limestone is the formation of numerous smaller shake holes and a some larger swallow holes, generally between 5-100 metres across, formed by the solution of limestone along joints in the rock, which join underground streams and watercourses.

In the moorland area to the north the soils mostly overlie Old Red Sandstone or sandstone drift deposits and are predominantly seasonally waterlogged, acidic, and with a peaty surface horizon, supporting wet moorland of poor grazing quality. Towards the west are smaller areas of better-drained land overlying sandstone in the Gwaun Cefnygarreg area and of better-drained land supporting moorland pasture of better grazing quality overlying limestone in the Garn Ganol area. Likewise, to the south, there are some areas of better-drained land overlying sandstone and limestone in the Cefn Cadlan and Mynydd-y-glog areas. In the lower-lying parts of Hepste and Cadlan valleys the soils are mostly derived from sandstone drift deposits and are generally slow draining and seasonally waterlogged loams.

A broad outline of the environmental and vegetational history of the historic landscape area since the last glaciation is indicated by a number of palaeoenvironmental studies that have been undertaken in the region, including pollen analysis of peat deposits on the south side of Pant Sychbant and buried soils near Nant-maden in Cwm Cadlan as well as a number of other sites in the Brecon Beacons and Fforest Fawr. The late-glacial and early post-glacial period between about 12000-6000 BC is marked by a sequence which saw the appearance of juniper scrub subsequently dominated by birch and then hazel-dominated woodland. The establishment of temperate woodland between about 6000-5000 BC also saw the arrival of oak and elm, of which oak became dominant on the lower-lying ground and pine and birch on higher more exposed elevations. It appears that post-glacial tree cover probably became patchy over a height of about 500-600 metres though some woodland would evidently have extended to over 800 metres, taking in the summit of Fan Fawr at the northern tip of the historic landscape area.

The first clear impact of human activity in the natural vegetation sequence in Fforest Fawr appears at a date of about 6000 BC during this warmer phase in the later Mesolithic, when it has been suggested that upland clearings were being created and kept open in birch woodland by burning and animal grazing. At about this time some areas of heather heathland and hazel scrub were also beginning to appear in areas that had once been wooded, probably at least in part due to human activity. Increased waterlogging in some areas also initiated peat formation and the rise of alder.

The period up to about 4000 BC, during the earlier Neolithic, saw a slight fall in elm and some other tree species with corresponding increases in grasses and herbs, and possibly an expansion of heathland. Intensified pressure on woodland is evident in the later Neolithic and earlier Bronze Age periods, between about 3500-1500 BC, with evidence for further increases in grassland, some ground disturbance, the continuing expansion of heather moorland but probably also the survival of some oak and hazel woodland at relatively high altitude. The continuing relatively mild climatic conditions during this period seem likely to have given greater potential for agriculture at higher levels than in the recent past and appear to coincide with the appearance of the early settlement and land use activity in parts of the historic landscape area.

This more favourable climatic phase began to deteriorate at about 1500 BC, during the middle Bronze Age, ending with cooler and wetter conditions which came into being in the period between about 1000-500 BC, loosely corresponding to the period of transition between the late Bronze Age and the early Iron Age. A shortened growing season and greater rainfall during this less favourable climatic phase probably led to the abandonment of early settlements and fields in some of the higher and more exposed parts of the area, which have since reverted to moorland. Wetter climatic conditions generally, however, appear to have led to increased waterlogging and a decline in soil fertility which inhibited woodland regeneration, though no doubt settlement and cultivation continued on more lower-lying and sheltered sites within the valleys.

A number of subsequent climatic fluctuations also seem likely to have had a direct impact upon the settlement and land use history of the area, such as a slight warming during the later Iron Age and Roman period, between about AD 0-400 AD and again in the Middle Ages between about AD 1150-1250, during which it is possible that some of the more marginal areas of settlement and land use that had been abandoned during the Bronze Age again became permanently settled for periods of several centuries at a time, only to be finally abandoned with the advent of worsening conditions during the ‘Little Ice Age’, between about AD 1300-1850, when cooler and wetter summers again imposed limitations particularly upon arable farming.

It has been suggested that the widespread acidic grassland which today dominates the unenclosed uplands of the historic landscape area were the result of relatively recent changes in grazing practice, replacing the heather moorland that had gradually spread and grown to dominance since the early prehistoric period. In medieval and earlier times it seems likely that the moorland was less intensively grazed, perhaps largely by cattle. Since about the end of the 18th and the beginning of the 19th century, however, intensive sheep farming has become dominant and is thought to have contributed to the vegetation change.

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