Birch is present in the form of two closely related species in Wales: downy birch (Betula pubescens) which prefers moist acidic soils and silver birch (Betula pendula) which prefers a wide range of light, well-drained, acidic soils. Birch trees are colonisers / pioneers, with stands often preparing the way for other woodland types, particularly where native conifers occur. In Wales, birch tends to occur either as discreet single-aged thickets in wetland and mire situations, such as dune slacks or raised bogs, or as a small component of other woodland types.

A birch -dominated form of the Natura 2000 ‘Bog woodland’ habitat occurs where birch occurs with bog vegetation. This is the case at Cors Caron in mid Wales, though whether this is a positive or negative situation is debatable.  It could be that the presence of the woodland indicates drying at the bog surface. It could also be that the spread of the trees will exacerbate drying of the bog surface.   Alternatively, it could be viewed as a natural phase of succession.  Either way, birch occurs naturally in these situations and could reasonably be considered a reference state.  Birch woodland is also found on degraded areas of bog.