The heathland within the site is classed as upland heathland, being above the 250m contour line. There is an estimated 79,000ha of this habitat extant in Wales, 1400ha of which occur within the Blaenau Gwent county borough (CCW 2003). This habitat type is, however, relatively scarce within the rest of Europe and has its stronghold in the UK. This habitat type often supports notable bird species including species such as hen harrier, red grouse and black grouse, although none of these species have been recorded to date at Sirhowy Hill.

The heathland habitats of the site are in a degraded condition, having been afforested throughout the site, and are now suffering from succession. The heathland habitats support seven plant species which are considered local in the region, and sixteen species considered indicative of species-rich heathlands and acid grassland mosaics in the Guidelines for the Selection of Wildlife Sites in South Wales (SWWSP 2004).