Hen-Allt Common is situated above the Wye valley, close to the town of Hay-on-Wye, within the Brecon Beacons National Park. It is positioned on a steep sided, north-west facing sandstone scarp and supports a good population of plant species that are rare and declining in Wales. It was designated as a Site of Special Scientific Interest (SSSI) in January 1991, and the Common is currently vested in the care of the Brecon Beacons National Park Authority as no person has come forward to claim ownership of the site.

• National grid reference: SO 233399
• Site area:                   11.8 hectares (29.2 acres)

The Brecon Beacons National Park Authority (BBNPA) and Countryside Council for Wales (CCW) are working as partners on a project to re-claim back Hen-Allt Common, before it naturally goes through successional change and returns to woodland, and many of the specialist species and habitat are lost.

The Common is currently, and has been for many years, dominated by bracken and scrub, under which CCW has reported probably the largest population of Meadow Saffron (Colchicum autumnale) known within any site in Wales.This particular species has declined drastically as a result of agricultural intensification within the UK. However, since the common has had no agricultural machinery, and no work to the land for over 20 years, the flower appears to be thriving, and it is hoped to bloom even further when the deep bracken litter is removed. Glades within the bracken also support numerous grassland types grasses and flowers.

The high sided slopes on the Eastern and South-East side of the common, support spring-fed mire communities which are characterised by various grasses, sedges, mosses and lichens. The site also contains the very rare Flat Sedge (Blysmus compressus) which is not known to grow anywhere else within Wales, so is of significant importance and makes the correct management of the site crucial for its continued existence in Wales.

Although BBNPA and CCW will be practically involved with the site for some years, the future aim is for the Commoners who have grazing rights for stock on the common, to be able to manage the site through conservation grazing and basic maintenance themselves. It is hoped that BBNPA and CCW will merely act as guardians of the site in the future, and the Commoners can undertake the necessary work to keep the common managed with both parties guidance.