Due to climatic, altitudinal and edaphic factors the vegetation of the sanctuary is unique and the major habitat types are West Coast Tropical Evergreen forests, West Coast Tropical Semi Evergreen forests, South Indian Moist Deciduous forests and Southern Hilltop Evergreen forests in addition to Grasslands and a few hundred hectares of unmaintained teak, eucalyptus and cashew plantations. The Hilltop Evergreen forests found at Ambalappara are in fact, shola-like in appearance, although the species combination is different. The diverse nature of the habitats within the sanctuary makes it home to an amazing variety of life forms.
Aralam Wildlife Sanctuary is the only protected area of the West Coast Tropical Evergreen forest of Dipterocarpus-Mesua- Palaquium type. Sanctuary holds a 25 sq.km of fairly undisturbed forest of this type. Paripputhodu, Uruppukunnu, Kannadivechakunnu and the whole stretch of forest from Chavachi to Ambalappara represent this forest type.