Blanket bog forms on deep peat in areas with high levels of precipitation and low evapotranspiration, in Wales, these conditions occur mostly in the uplands of north and west Wales. Blanket bogs in the Welsh mountains lies over undulating as well as in wet hollows and often forms large scale mosaics with dry heath and acid grassland. The habitat is generally species-poor and typically dominated by bog mosses (Sphagnum spp.), ericoids such as Ling (Calluna vulgaris) and cross-leaved heath (Erica tetralix) and cotton grasses (Eriophrum spp.). The largest areas of blanket bog in Wales are in the Berwyn and Elenydd and Eryri mountain ranges, though the habitat can often be fragmented and degraded, particularly in Elenydd. At best, the habitat forms patterning that resembles the hummock and hollow complex of raised mires. However, large areas of blanket bog in Wales show signs of degradation with impoverished areas dominated by grasses. The main causes of degradation in the past have been drainage and burning to create better habitat for grazing, peat cutting for fuel and compost, and afforestation, though climate change also poses a threat if precipitation levels fall and warming occurs.