Southern tropical thorn forest (Scrub jungle)
This is the least distributed forest type in Kerala and is the second major forest type in the Sanctuary with regard to the area. The open low forest type is characterized by xerophytic species with short bole and low branching. The canopy is wide open. Therefore the canopy level differentiation is indistinguishable. The hardwood trees, thorny shrubs and climbers are characteristic features of the forest type. The undergrowth is furnished with some herbaceous forms during monsoon and remains exposed for the rest of the time. This forest type is distributed at Chinnar, Champakkadu, Chungam, Nellimedu and on the slopes of Alampetty, Eachampetty, Palapetty etc.
The major species representing the forest type are Acacia spp.,Euphorbia spp.,Capparis spp.,Opuntia spp., Ziziphus spp., Grewia spp., Cordia spp., Albizia amara, Atalantia monophylla, pleiospermium alatum, Prosopis juliflora, Dichrostachys cinerea, Diospyros cordifolia, Pisonia aculeate, Carissa carandas, Strychnos potatorum, Ceropegia juncea, Pergularia daemia, Caralluma spp., Helixanthera spp., etc
Southern dry mixed deciduous forest (Dry deciduous forest)
The forest type is characterized by predominant hardwood deciduous tree species. The canopy is open with poor undergrowth. Bamboos are barely represented. The canopy level is vague in this type also. This is the dominant forest type in the Sanctuary constituting nearly 30%. It is found near settlements of Palapetty, Alampetty, Eachampetty, Karimalai, Thayannankudi, Puthukudi etc.
The most characteristic species present invariably in the forest type are Anogeissus latifolia, Chloroxylon swietenia, Hardwickia binata, Boswellia serrata, Santalum album, Cassia fistula, Sterculia urens, Sapindus emarginatus, Canthium coromandelicum, Tarenna asiatica, Dodonaea angustifolia, Garuga floribunda, Shorea roxburghii, etc.
Southern moist mixed deciduous forest (Moist deciduous)
The closed high forest is characterized mostly by deciduous plants, only for a brief time compared to the above forest type. The forest type covers less than 8% area of the sanctuary at Palapetty, Karimalai, Puthukudy, Eachampetty, Alampetty etc. The occasional occurrence of some of the characteristic tree species of the forest type along with the notable absence of some predominant trees like Terminalia spp., Xylia xylocarpa, Careya arborea and Dillenia
pentagyna might be due to the clearance of this forest type for converting to agricultural purpose. The view is strengthened because most of the agricultural areas are lying mixed with this forest type.
The upper canopy trees are Grewia tiliifolia, Schleichera oleosa, Wrightia tinctoria, Bridelia crenulata, Buchanania lanzan, Pterocarpus marsupium, Gmelina arborea, Stereospermum colais, Albizia odoratissima, etc. The species forming the middle canopy include Premna tomentosa, Atalantia racemosa, Cipadessa baccifera, Clerodendrum serratum, C. viscosum, etc. The undergrowth constitutes Helicteres isora, Desmodium velutinum, Indigofera pulchella, Rhinacanthus nasutus, Justicia betonica, etc
Tropical riparian fringing forest (Riparian forest)
The forest type is characterized by a few evergreen and semi-evergreen species restricted on the sides of streams forming a narrow fringe. In the Sanctuary, the forest type is restricted mostly along the side of the Pambar and Chinnar rivers.
The dominant species are Terminallia arjuna, Hopea parviflora, Bischofia javanica, Mangifera indica, Drypates roxburghii, Vitex leucoxylon, Pongamia pinnata, Garcinia gummi-gutta, Mallotus stenanthus, Calophyllum calaba, Entada rheedei, Lepisanthes tetraphylla, Syzygium cumini, Schefflera racemosa, Homonoia riparia, Vitex altissima, Salix tetrasperma, Gnetum ula, etc.
Southern montane wet temperate forest (Hill shola forest)
The high altitude evergreen closed forest is characterized by short boled and branchy species. The attractive canopy of the shola species in varying shades of red is really a fascinating view and is also one of the conspicuous features of this forest type. The forest type is localized at three places, Olikkudy shola, Kariveppin shola and Koyman shola at altitudes above 1300 m. This is the only undisturbed forest type in the Sanctuary covering about 0.25% of the total area. There is no marked differentiation of canopy layers.
The dominant species of the forest type are Syzygium spp., Elaeocarpus recurvatus, Actinodaphne malabarica, Agrostistachys indica, Fagraea ceylanica, Cryptocarya anamallayana, Calamus gamblei, Pittosporum spp., Gordonia obtuse, Mallotus tetracoccus, Aglaia elaeagnoidea, Gomphandra coriacea, Microtropis parviflora, Meliosma pinnata, Rhodomyrtus tomentosus, Mussaenda tomentosa, Ardisia pauciflora, Cinnamomum verum, Litsea wightiana, Cassine paniculata, Ficus amplocarpa etc.
Southern montane wet grassland (Grasslands)
The high altitude natural grasslands are located along the boundary with Eravikulam National Park above Olikkudy and along the south-eastern extremity above Mangapparakudy. The predominant species are Arundinella mesophylla, A. setosa, Apluda mutica, Ischaemum nilagiricum, Setaria pumila, Themeda triandra, Cymbopogon flexuosus, Echinochloa colona, Digitaria wallichiana, Chrysopogon zeylanicus, Viola betonicifolia, Pimpinella candolleana etc.