The major block of 4,000 ha of native forest in south-west Mauritius that lies to the south and west of the Black River Gorge system is included in this site, together with adjacent exotic vegetation. Physically, the site comprises the south-facing escarpment leading from the southern coastal lowlands to the central plateau, between the Rivière Savanne at Combo in the east and the village of Chamarel in the west, and also the following linked areas: at the top of the escarpment, Plaine Champagne and Black River Peak; the Black River Gorge system west of the Rivière Noire and Grandes Gorges River; and the southern part of the Bois Sec Basin (but the isolated Bois Sec Nature Reserve is included in IBA MU004, together with the relict forests of the central plateau). Three peaks line the top of the escarpment, from west to east: Black River Peak (824 m, the highest point on Mauritius), Montagne Cocotte (772 m,) and Piton Savanne (704 m). Vegetation is mainly mixed montane forest; this includes cloud-forest on Montagne Cocotte (the wettest site on Mauritius: 5,000 mm of rainfall annually) and rainforest between Piton Savanne and Upper Bel Ombre. Dry evergreen lowland forest occurs in the north and west (as rainfall decreases rapidly westwards), with heterogeneous montane shrubland, bushland and thicket in exposed areas such as Plaine Champagne. Most of the native vegetation is within the Black River Gorges National Park. Much land outside the park is privately-owned, and some is used for deer-hunting.
See Box and Table 2 for key species. All eight threatened and near-threatened native landbird species of Mauritius occur at the site: Falco punctatus (30 pairs in 1998), Columba mayeri (137 birds in 1998, c.50% of non-captive total population), Psittacula eques (visits much of the area and nests in Bel Ombre), Collocalia francica (uncommon breeder), Coracina typica (120–220 pairs, c.60% of world population, 1993), Hypsipetes olivaceus (120–170 pairs, c.50% of world population, 1993), Zosterops chloronothos (90–185 pairs, c.70% of world population, 1993), Foudia rubra (93–108 pairs, c.90% of world population, 1993). The high proportion of global populations found at this site make it one of the world’s most important for threatened bird species. All 10 of the restricted-range species occur at the site, including Terpsiphone bourbonnensis (10–30% of world population of race desolata, 1993) and Zosterops borbonicus (abundant). The native passerines are concentrated on the escarpment between Montagne Cocotte and Piton Savanne. The world population of Columba mayeri was, until 1987, restricted to the same area; one of three new populations established by reintroduction since 1987 is also at this site (Bel Ombre). This is also the only breeding site for Psittacula eques away from Macchabé–Brise Fer (IBA MU003).
Non-bird biodiversity: Endemic plant communities, all rich in rare and endemic species: rainforest (very diverse, largest area on Mauritius at this site); cloud-forest (unique community on Montagne Cocotte—this and rainforest support several plant species known nowhere else; south flank of Cocotte may have the richest and least degraded forest on Mauritius); other mixed montane forest (Black River Peak and Bel Ombre); montane shrubland or bushland and thicket (Plaine Champagne); dry evergreen lowland forest (north and west of Black River Peak). Reptiles: Phelsuma guimbeaui, Phelsuma rosagularis, Phelsuma cepediana, Gongylomorphus fontenayi (all endemic).Mammals: Pteropus niger (VU), Mormopterus acetabulosus (VU).
Pressure/threats to key biodiversity
Most of the native vegetation is protected by the Black River Gorges National Park. However, an area critical for native wildlife (the Mountain Reserve on the south-facing slope between Montagne Cocotte and Piton Savanne, including Bassin Blanc Crater Lake) is excluded. The native forest of the western slopes of Black River Peak is also in the Mountain Reserve. Small groves (most a few hectares) of exotic plantation trees surrounded by native forest are of vital importance for native birds (especially Foudia rubra), as they support higher nesting success than surrounding native forest. These include the 6 ha grove of Japanese Red Cedar Cryptomeria japonica near Piton Savanne, which supported all wild breeding by Columba mayeri until reintroduced populations were established elsewhere. The worst invasive weeds are Psidium cattleianum and Ligustrum robustum. The vegetation of the most bird-rich areas is severely degraded, and exotic animals including mammalian nest-predators abound. Management and reintroduction programmes are or have been taking place for non-passerine birds, and areas of native vegetation selected for intensive management and rehabilitation, benefiting all wildlife.
BirdLife International (2019) Important Bird Areas factsheet: Black River Gorges National Park and surrounding areas. Downloaded from
http://www.birdlife.org on 20/08/2019.