Location: Within the Elan Valley Estate Grid Ref: SN857756 Access: Contact the Ranger's Office prior to visiting these environmentally sensitive and potentially hazardous habitats. Contact: Elan Valley Visitor Centre, Elan Valley, Rhayader, Powys, LD6 5HP.Rangers' Office: 01597 810880 Website: www.elanvalley.org.uk

Within the bog lands of Wales, scientists have found evidence which helps them to paint a picture of the country's environmental past. Big pieces of ancient pine and alder have been found in the upland bog of Bryniau Pica, east of Pontrhydfendigaid, indicating that even the uplands of Wales were covered in thick woodland thousands of years ago.

These thick forests were probably at their height around 7,000 years ago but, during the Neolithic areas, were cleared to house tombs and enclosures and increasingly to provide farmland.

By the Bronze Age around 4,000 years ago, trees were in the minority and large open areas were increasing.

It is thought that both climate deterioration and human activities were responsible for turning many of these areas into bog land. Grazing animals and clearing and burning changed the water balance of the uplands.

Trees act as umbrellas so rain that lands on leaves sometimes evaporates without even touching the soil. Without the trees, the soil gets wetter.

In the Middle Ages, Cistercian monks grazed their numerous sheep on the bogs during the summer and are probably responsible for the bog erosion.

At Gors Lwyd, there is an example of bog formed after the last glaciation and a blanket bog that was probably caused by the activities of man.