The site, which is on the Jurassiclimestone of the western Cotswolds, is a diverse area of ancient beech woodland, unimproved grassland, scrub and disused quarries. Bull Cross is unimproved calcareous grassland; The Frith is broadleaved woodland which comprises mostly beech, and Juniper Hill supports ash, scrub, unimproved calcareous grassland and old quarries.
Frith Quarry is a nationally important geological site providing exposures of Middle Jurassic rocks. These are considered to be of great significance in interpreting the Inferior Oolite succession of the Cotswolds. Specimens collected, and the exposures of Oolite Marl and Lower Trigonia Grit, have provided rich brachipod and ammonite faunas. The ammonite faunas are significant in the Cotswolds being rare, and thus the site is important for geological research into the Jurassic period.
The name 'Frith' is Saxon for a wooded enclosure. The wood has probably been managed as mixed wood-pasture and beech coppice since those times. The current high forest aspect originates from beech seed which was planted after the Napoleonic Wars. The beechwood successful regeneration, and its rich flora and fauna, provide a good example of ancient woodland in the Cotswold area. An 'Arcadian' retreat was created in Frith Wood in the mid-1700s by Benjamin Hyett of Painswick House. This is called 'Pan's Lodge' being dedicated to Pan, god of wine, the pursuit of pleasure. A painting by Thomas Robins of 1757 shows a small house overlooking the 'Panswyck' valley. This is surrounded by 'elegant' woodland walks and a plantation. Frith Wood was 'renamed' at the time to Coldbourn Grove. The site had disappeared by the 1820s and only a mound is left. Some of the garden plants remain growing in the woodland. There is a small old quarry in Frith Wood which was probably used for enclosures walls and even for building Pan's Lodge. The old road from Birdlip to Stroud passed through Frith Wood Common until the turnpike was opened in the 18th century.
Fauna
Birdlife includes wood warbler, marsh tit and green woodpecker. The molluscs recorded are Limax cinereoniger and Zenobiella subrufescens, which are species occurring in ancient woodland. The lapidary snail is also recorded. Hundreds of varieties of fungus have been found in the reserve.
Conservation
Regeneration has been a natural process as part of the management plan since 1960. This is supported by selective thinning and felling of some mature timber trees. Invasive sycamore has been controlled by methods to leave standing dead wood and also removal.
Publications
Kelham, A, Sanderson, J, Doe, J, Edgeley-Smith, M, et al., 1979, 1990, 2002 editions, 'Nature Reserves of the Gloucestershire Trust for Nature Conservation/Gloucestershire Wildlife Trust'
'Frith Wood – Morley Penistan Nature Reserve – A magnificent ancient beechwood',, Gloucestershire Wildlife Trust