The northern part of the reserve was purchased by the Radnorshire Wildlife Trust in 1973, the wood is part of a much larger block of woodland typical of the uplands of this part of mid-Wales. Though shown on the 1939 tithe map of St. Harmon it is clear that large sections have been clear-felled during the first and second World Wars. In 1982, the southern part was purchased and in 2004 the middle section called Cwm-yr-Ychen was purchased linking up the acid sessile oak woodland nature reserve.
Sessile Oak woodland dominates the reserve with Rowan a common species. Bilberry and Cow-wheat are frequent in the ground layer as is the moss Rhytidiadelphus loreus. This is an internationally important reserve for lichens. This is the sole site in Radnorshire for the nationally scarce Biatora chrysantha and this is only one of two sites in Wales where the Bryoria subcana, Usnea glabrescens and Pertusaria opthalmiza lichens are found.
Breeding birds (34 species) include Pied Flycatcher, Wood Warbler, Redstart, Spotted Flycatcher, three species of Woodpecker, Tawny Owl, Coal Tit, Nuthatch, Treecreeper, Song Thrush and Mistle Thrush. Visitors include Sparrowhawk, Buzzard, Raven and Cuckoo.
The Cow-wheat Shield Bug Sehrius bigutatus and brassy coloured Ground Beetle Calosoma inquisitor are found along with the oak feeding Longhorn Beetle Leiopus nebulosus. The Green Oak Tortrix Moth Tortrix viridaria is common, its caterpillars providing an important source of food for birds in the spring. Galls are frequently encountered including Common Spangle Gall, Silk Button Gall, and Oak Apple Gall.
Take the B4518 from Rhayader to St. Harmon. In Pant-y-Dwr, take the first left after the Mid Wales Inn (just before the bus shelter). Follow this road for 1.3 miles and go straight ahead onto a forestry track. Don't follow the road to left. Drive past the property and into the plantation area. Park in the first lay-by pn the right (NGR: SN 964 759). The nature trail marked by wooden posts begins here.
NGR: SN 966 762