Natural vegetation of this sanctuary is a combination of Malabar and Deccan elements.
Micro climatic fluctuations coupled with edaphic, topographic and biotic factors have endowed this sanctuary with rich floral diversity.
The natural vegetation growing in this sanctuary has been classified into following types:
||West coast tropical evergreen forests
||West coast tropical semi-evergreen forests
||Southern moist mixed deciduous forest
||Southern dry mixed deciduous forests
||Moist bamboo brakes
||Southern montane wet temperate forests (Sholas)
In addition, this sanctuary harbours three minor vegetation types of which two are man-made. They are:
- Low altitude marshy grass lands known locally as vayals
- Teak plantations
- Eucalyptus plantations
The evergreen and moist deciduous forests are the most important natural vegetation types. Sholas are confined to small areas in the hilltops of Karimala Gopuram and in the foothills of Pandaravara peak which is known by the name Karian Shola.
West coast Tropical Evergreen Forests
This type of forests is found in areas wherever humidity and soil moisture conditions are favourable, rainfall is 1500-5000mm or more and altitude is 250 to 1200m. The main forests of this type are found in the Orukomban range and they fall under the core zone of this sanctuary. These evergreen forests are contiguous with the evergreen forests of adjoining forest divisions of Chalakkudy and Nemmara.
Karimala is another important region, where evergreens meet with grasslands. At Pooppara, it is in continuation of the evergreen forests of the Vazhachal forest division. Small patches of the evergreen trees are also found within the moist deciduous localities such as Parambikulam, Vengoli, Karianshola and Pulickal areas. Total extent of these forests is about 50 sq. km, normally seen at 800 m above mean sea level in this sanctuary.
Evergreen forests exhibit luxuriant growth, and closed canopy of trees and woody climbers. High humidity, shade and sheltered conditions provide ideal habitat for epiphytes as well as terrestrial orchids, ferns, mosses and other herbaceous flowering plants. The quantity of epiphytes and mosses tend to increase with the increase in altitude, while the number of woody climbers decrease. The main character of these evergreen trees is to develop buttresses at the base of the bole. In addition to these, many streams are originating from these forests.
In these forests, the trees with varying heights show stratification. There is dominance of certain species in the upper stratum. The important associations noticed are, as under:
Mesua - Cullenia – Calophyllum
Palaquium - Mesua
Palaquium - Calophyllum
Mesua - Cullenia
Hopea - Vateria
Vateria - Calophyllum
West coast Tropical Semi-Evergreen Forests
This forest type is spread over an area of 20 sq. km approximately. There is no clear-cut area of semi evergreen forests. These forests appeared to be ecological zones in areas where the moist deciduous forests merge with evergreen. Thus these forests represent a transitional zone between evergreen and moist deciduous forests. Lofty trees with thick and buttressed tree trunks are found growing with cylindrical bole. The ground floor of semi evergreen forests receives more light than the ground floor of evergreen forests, due to comparatively lighter canopy. Due to variation in the mixture of species of evergreen forests and deciduous Forests, it becomes difficult to determine the exact status of these forests.
Southern Moist Mixed Deciduous Forest
The chief feature of the moist deciduous forests is a leafless period in the dry season which may or may not begin with the cold weather. These forests have spread over an area of 60 sq.km. of the Sanctuary, over the ridges and lower slopes having elevation of 100m to 400m where the soil is generally rich. The top canopy remains leafless between March and May. Over most of the areas, teak plantations have been raised after Clear felling the indigenous species, growing in these forests, from 1913 to 1983. Naturally growing moist teak was one of the dominant species present in these forests. Kannimara teak tree having girth of 6.48 m and height 48.75 m is one the largest natural teak trees in Asia, which the tourists visit. In order to represent the old natural growth of Teak trees a plot has been preserved in Sungam range. It has been observed that the teak trees in the preserved plot have attained huge dimension and high floral diversity. In the past these forests have been exploited heavily. To start with, selected Teak and rose wood trees were felled and timber was extracted. No serious attempt was made to regenerate these species. Later on, when timber demand for these species increased, the forest areas were clear felled and mostly teak plantations were raised on these areas.
Physiognomically, the moist mixed deciduous forests have a closed canopy with tall and cylindrical trees. Trees tend to attain a height of 30.4 m and more. The under storey is well defined and the forest floor is full of vegetal growth. It has been observed in Anappady, Elathode and interstate boundary area that the floral elements of dry deciduous forests consisting of Anogeissus, Bombax, Tamarindus etc., exist within the Moist deciduous forests.
In Vengoli, Thellickal, Pulickal and Pooppara areas a good quality teak, rosewood, terminalias and Schleichera grows in depressions having rich soil. Bamboos also grow in abundance. In drier locality such as Anappady, Elathode, Thellickal east etc. Anogeissus, Albizzia, Sterculia, Grewia and Emblica trees are common. Bamboos are also found in dense thicket formations extensively. In areas such as Orukomban and Kothala, trees such as xylia xylocarpa and Grewia tilifolia come up in localized lateritic patches. The main species that are found in these forests are given below.
Southern Dry Mixed Deciduous Forests
This type of forest is attributed to relatively low rainfall and lower altitude i.e., 300m-400m above MSL. Many species growing in this forest type are common to the moist deciduous forests. However their percentage of occurrence is low. The leaf-fall starts earlier as compared to moist deciduous forests. This is due the quantity of rain received till the end of North-East monsoon. Generally the trees remain leafless between January and May. Physiognomically, the dominant trees attain height 18.3m to 24.4m and are not gregarious. The canopy is comparatively open allowing good percentage of grass and herb to grow. Bamboos occur as under growth which are heavily browsed and become bushy. New culms of Bamboo grow during November - December. These forests are highly prone to fire. By December and January the grass and many herbs dry up and leaf fall starts too. The forest floor is thickly covered with dry twigs and leaves. As tribal settlements and estates are located in the vicinity of these forests. Forest fires are common due to high degree of biotic interference. Due to repeated forest fires in the past, the forests have degraded and thus a few fire-hardy species are growing in these areas.
The north east portion of this sanctuary adjacent to the plains of Tamil Nadu has a small patch of this type of forests covering about an area of 15 sq.km around Thekkady and Keerappady.
Miscellaneous and Man-made Vegetation types
The brakes are often dense, even if the bamboos grow in clumps. Bamboo brakes are usually found along streams or on badly drained hollows more or less displacing the tree forest. More or less continuous cover of one or two species of tall clumped bamboos with occasional standard of Terminalias and other trees are found. The moist bamboo brakes are sufficiently aggressive to be able to hold against tree growth. The latter probably gains ground after good seed years, so that very gradually the bamboo ceases to dominate.
Bambusa arundinacea, the only bamboo has come up in highly fertile and well drained soil in Muduvarachal, Pulickal, Kothala, Pooppara, Vengoli and Thellickal areas of this sanctuary. The Natural bamboo brakes also occur along the stream banks, reservoir banks and in sheltered depressions. Vengoli has the largest area of such bamboo brakes in the Sanctuary. In Elathode,Thellickal east and Thekkady areas where habitats are comparatively dry Dendrocalamus strictus is growing. D.strictus (Kal-mungil) is not growing gregariously like Bambusa arundinacea, but it is heavily browsed, so it has acquired the shape of thicket. However, its regeneration is satisfactory.
Bambusa arundinacea follows a flowering cycle of 28 to 30 years in this sanctuary. In the working plan for South Coimbatore Forest Division, Srivenkateswara Iyer has reported gregarious flowering in Anamalai during 1926-30 AD which adjoins this sanctuary. Later on, during 1956AD, sporadic flowering was reported initially, which turned gregarious later on, and thus bamboo clumps dried. These dried bamboos were collected by M/s. Gwalior Rayons Company. Again gregarious flowering started from 1983 AD and continued till 1985. About 20000MT dried and flowered bamboo culms were allotted to M/s. Hindustan Newsprint Limited.
The areas occupied by the bamboo, have regenerated satisfactorily. The clumps are congested, as no thinning of culms is done. After 1984-85, gregarious flowering was again notices in Keerapady during 2000. Such areas need special attention and management strategies.
8A/C1/E1 - OCHLANDRA REED BRAKES
The reed grows into impenetrable thickets of 3m to 5m height with scattered over wood of evergreen trees. They are restricted to moist areas. Unlike bamboos, the reed brakes occur in high altitude within evergreen forests. The stream banks and the areas under the shelter of evergreen and semi evergreen forests of Pooppara, Karimala, Pulickal, Orukomban and Muduvarachal support reed brakes. The reed does not grow gregariously and its height varies between 2m - 4m. Around the stream banks they occur densely.
The following species are found in the sanctuary viz., Ochlandra rheedii (Ottal, Kolangi), Ochlandra travancorica (Eetta) and Ochlandra brandisii.
There is no problem of regeneration. However, the local tribals use reed for their household purposes. Reeds are not exploited commercially now. Muduva tribals collect and use them for making baskets, roofing materials, carpets etc. for their bona fide domestic requirements.
11A/C1 -SOUTHERN MONTANE WET TEMPERATE FORESTS (SHOLA FORESTS)
Shola forests are unique montane vegetation occupying temperate habitats in tropical latitude and are communities restricted to valley and depressions especially along the folds of hills. Karimala hills of this sanctuary has some resembling characteristics of this type. The forest restricted to Karimala hills, is not a true shola, according to forest type description, but it shows important characters of shola plants i.e., stunted short boled highly branched trees, clothed with mosses and other epiphytes. Woody climbers are few. There is no stratification for trees and leaves are mostly small.
The species growing in this type of forests are given below.
Cinnamomum sulphuratum, Euonymus indicus, Ligustrum robustum (rox burghii), Mesua indica, Symplocos cochinchinensis, etc.
Lycopodium phlegmaria, Bulbophyllum fusco-purpureum, Bulbophyllum tremulum, Eria clavicaulis, Eria reticulate, Oberonia denticulata, Oberonia lindleyana, Dendrobium chlorops, Dendrobium nutans, D.viridiflora etc.
Impatiens parasitica, Peperomia tetraphylla and other species of palatable grasses are in abundance.
11A/C1/DS2- SOUTHERN MONTANE WET GRASS LANDS
The grasslands are viewed as a stable degradation stage of vegetation because of the reasons such as recurrent fire, high wind velocity and shallow soil on the top of high altitude undulating terrain. This type of montane wet grasslands are confined to hill-top of Karimala Gopuram, Vengoli and Pandaravarai areas of this sanctuary. The vegetation is dominated by grasses along with several herbaceous and sub-shrubby species.
The main species that are found are given below:
Arundinella leptochloa, Chrysopogon asper, Cymbopogon flexuosus, Sacciolepis indica, Themeda triandra, Zenkeria elegans etc.
Aeginetia pendunculata (Keeripu), Andrographis neesiana, Arisaema tortuosum, Cajanus lineata, Drosera peltata (Peltate sundew), Eriocaulon setaceum, Habenaria barbata or H.travancorica, Pogostemon rotundatus, Peucedanum anamallayense, etc.
Hypericum mysorense, Lobelia nicotianifolia, Osbeckia cupularis or O.zeylanica or O.glauca or O.aspera etc., are common occurrences. Phoenix loureirii, a curious palm is commonly found in this area.
LOW ALTITUDE MARSHY GRASS LANDS -VAYALS
In Malayalam, low altitude marshy grasslands are termed as Vayals which are unique features of the sanctuary. Here, grasses and sedges provide high- density feeding ground for the wild herbivores during the lean season also.
Some of the species growing in vayals are given below:
Axonopus compressus, Paspalum spp. and Eragrostis spp.
Sedges (Family: Cyperaceae)
Lipocarpa argentea, Fuirena umbellata, Fimbristylis tetragona, or F.accuminata or F.junciformis, or F.dephylla, Cyprus cuspidatus or C.difformis or C.tegetum, Rynchospora corymbosa (coarse and unpalatable species).
Justicia spp., Ludwigia, Hygrophile, Ageratum, Eupatorium odoratum (Nilgiri weed) and Parthenium hyterophorus (Congress grass).
Moist deciduous tree species such as Butea, Careya, Mitragyna, Adina and Terminalia and Bamboos are seen invading along the fringes of the Vayals. Similarly the central marshy portions of vayals are being excessively invaded by coarse and unpalatable sedges especially the species Rhyncospora corymbosa. This endangers the status of palatable grasses in the vayals and hence need special attention.
Teak (Tectona grandis) Plantations
The valley and the lower hills of the sanctuary were planted with teak after clear felling the moist deciduous, evergreen and semi evergreen forests in patches. Teak plantations ranging from year of formation 1921 to 1983 exist in the sanctuary. The total area under teak is 8559. 215 Ha.
Over a period of time, 81.507 Ha of dry deciduous forests in the Elathode section of the sanctuary had been converted into eucalypts plantations. Most of these eucalypts plantations have been clear-felled. These plantations however are not of any practical utility for the wildlife since they lack food source even in their under storey.