The site lies west of Toamasina and south of Fito, with mid-altitude mountainous massifs rising to 1,500 m. Three permanent and fast-flowing rivers run across the reserve—the Sanalaotra, Marongolo and Ranomena—and include some waterfalls. The forest in the southern and western parts is not easily accessible, as it is on very steep terrain. The vegetation is composed of low- and mid-altitude, dense, humid evergreen forest. Low-altitude forest is characterized by canopy trees of Sarcolaenaceae, Myristicaceae and Anthostema, and mid-altitude forest by trees of Burseraceae, Myrtaceae, Monimiaceae, Ebenaceae and Cunoniaceae. Some parts are covered by mosaics of old secondary forest. The watersheds, especially in the northern and north-eastern parts, have been cleared of forest recently, and are (in some places) covered by secondary forest, dominated by Harungana and traveller’s palm Ravenala.
See Box and Tables 2 and 3 for key species. Seventy-eight species are known from the site, of which 49 are endemic to Madagascar. Two of the species are restricted to the north-eastern forests of Madagascar: Coua serriana and Oriolia bernieri. Little is known of the site’s avifauna.