The site includes patches of native vegetation, covering up to 210 ha, scattered over the southern part of the central plateau (350–700 m). They are either isolated mountain peaks unsuitable for forestry (Piton du Milieu, Montagne Lagrave, Montagne Laselle, Montagne d’Hauvillard, Kanaka Crater); areas saved from clearance because of botanical importance (Bois Sec, Les Mares, Gouly Père, Perrier); or areas saved for reasons not documented (Rivière du Poste, Jouanis, Monvert). The whole region is very humid and various native plant communities are represented, as well as spectacular landscapes such as the exposed volcanic plug of Piton du Milieu and the very sharp ridge of Montagne Laselle. Ranching and hunting of deer are limited to a few of the patches. Several patches are reserves. The native forest of State Land Monvert and Montagne Lagrave is fenced.
See Box and Table 2 for key species. Seven threatened or near-threatened species are present, with important populations of three: Hypsipetes olivaceus (widespread at very low density in native and sporadically exotic forest 15–24 pairs, 1993); Zosterops chloronothos (exploits small areas of suitable habitat, but not known east of Montagne Lagrave, 30–70 pairs, 1993), Foudia rubra (Grand Bassin and Rivière du Poste only, 6–7 pairs, 1993). Of the remaining threatened/near-threatened species Psittacula eques is arare non-breeding visitor (probably visits only when preferred food-plants are fruiting), Collocalia francica is probably an uncommon breeder, Coracina typica (Bois Sec and Grand Bassin only, disappeared from remoter patches since 1975, 4–6 pairs, 1993). The eight restricted-range species at the site include Terpsiphone bourbonnensis (small numbers, also in exotic river valley vegetation, 6–30 pairs, 1993) and Zosterops borbonicus (abundant). The site’s importance for birds is disproportionate to its small area. The richest native bird communities were (in 1993) found in patches nearest the main south-western forest block (‘Southern slopes’ IBA, MU002). It is the main area for the near-threatened exotic Anas melleri on Mauritius (small, introduced population, especially near Piton du Milieu).
Non-bird biodiversity: Endemic plant communities, all rich in rare and endemic species: cloud-forest (on Montagne Lagrave, highest native pteridophyte diversity in Mauritius); rainforest; other mixed montane forest (at Perrier, finest ‘Sideroxylon formation’); montane shrubland (on Montagne Laselle, very rare heath community). Many extremely rare plants are known from these sites (in several cases, only one site), for example Tectiphiala ferox (monotypic palm genus, E). Reptiles: Phelsumarosagularis, Phelsuma cepediana (endemic). Mammals: Pteropus niger (VU), Mormopterus acetabulosus (VU).
Pressure/threats to key biodiversity
Three Nature Reserves—Les Mares (5.1 ha), Gouly Père (10.9 ha) and Bois Sec (5.9 ha)—are strictly protected, although isolated from each other and from the National Park by exotic vegetation; all three contain threatened birds. Surrounding forestry areas are privately leased for deer-hunting, providing further protection. Perrier Nature Reserve (1.5 ha) is too small and isolated to be of importance to birds, and the small size of most patches makes several native bird populations of doubtful viability (especially Coracina typica and Foudia rubra). The usual invasive plant and mammal species cause problems; the Montagne Lagrave area is especially infested with traveller’s palm Ravenala madagascariensis. Deer-ranching and -hunting affects Piton du Milieu, Rivière du Poste, and Jouanis, possibly also Laselle.
BirdLife International (2020) Important Bird Areas factsheet: Relict Forests of the Central Plateau. Downloaded from
http://www.birdlife.org on 25/09/2020.