Briarwood Banks is one of the best examples of rare, semi-natural woodland in Northumberland. Ash dominates, although oak and birch are common. Typical ancient woodland plants include ramsons, woodruff and dogs mercury. The woods around here provide the most northerly habitat for dormice and you may also see red squirrels and roe deer. Birds such as pied flycatcher and great spotted woodpecker can also be seen.
Semi-natural ancient woodland is a relatively rarity in Northumberland; this reserve is probably one of the best examples in the county. The woodland supports a diversity of plant species which reflect the variation in soil conditions. There are a number of locally uncommon species including two regional rarities: bird's-nest orchid and wood fescue. Other uncommon plants such as herb Paris and toothwort are present along with a very good bryophyte flora and several rare, ancient woodland indicator lichens. An area of the woodland planted with non-native species is being restored to provide suitable conditions for a range of rare species including dormouse which is found in neighbouring woodland, their most northerly location in the UK. Near the River Allen are the remains of an old lead smelt mill. The grasslands have been contaminated by heavy metals derived from the Pennine orefield upstream. Plants indicative of this contamination include mountain pansy and alpine penny-cress.