Atolls are made up of porous coral rich in lime and possess a climate that is hot and dry. Trees grow up through cracks in the rocks. Deep in the valleys, aerial roots of Ficus trees stretch downward, forming prop root forests. Mountain slopes are scoured by rainwater, creating buttresses. Along windy ridges, thorny forests develop, composed of plants with coarse, small, dry leaves. Atoll species exhibited in this area include Diospyros philippensis, Palaquium formosanum, Drypetes littoralis, Aglaia formosana, Dendrocnide meyeniana, Ficus benjamina, Ficus tinctoria and Longflower justicia.