The site includes the Somerset Wildlife Trust's Mounsey Wood Nature Reserve and the Knaplock and North Barton SSSI which has been notified since 1954.

The Barle Valley, which consists of steep sandstone slopes with acidic soils, contains large areas of ancient upland of Sessile Oak woodland.

Over Eighty-five different types of vascular plant species have been recorded in the area, including thirty-one ancient woodland indicators.

The mires are fed by springs which flow from the base of the sandstone slopes and are dominated by moss carpets due to their low-nutrient environment.

Due to a large amount of ancient woodland indicators in Barle it gives it a very high index of ecological continuity.