Parcel I of Andohahela National Park is located 84 km north-east of Tolagnaro. It includes a portion of the mountainous massif of Beampingaratra, oriented north–south, and five peaks above 1,500 m. The main river rising in the parcel is the Mandrare, augmented by the waters from its two tributaries, the Mananara and the Manambolo. In the east, the Manampanihy and Andriambe rivers flow respectively towards the north-east and the south-east. The vegetation is composed of low- and mid-altitude, dense, humid evergreen forest, dominated by trees of Tambourissa, Symphonia and Dalbergia, although the steep slopes are dominated by Lauraceae, Compositae, Rubiaceae and Convolvulaceae. Tree-ferns and orchids are common, and epiphytic cacti Rhipsalis also occur.
See Box and Tables 2 and 3 for key species. Eighty-seven species are known from the site, of which 57 are endemic to Madagascar. The site is the southern limit of the distribution of several species, in particular those which are characteristic of montane forest. The site holds four species of ground-roller (Brachypteraciidae), two species of Neodrepanis, Randia pseudozosterops, Cryptosylvicola randrianasoloi, nine species of vanga (Vangidae) and Newtonia fanovanae.