 The third zone, Tsimelahy, is mainly at an altitude of , contains the unique Ranopiso transitional forest.The mountains form a natural barrier to the moist trade winds that blow from the east, causing a rainfall of per year on the eastern side that supports one of the few rainforests south of the Tropic of Capricorn.At the western edge of the park, the rainfall is just per year and the resulting vegetation is a dry spiny forest characteristic of southern Madagascar.