Sunday, August 3, 2008

Kerala - Forest

Wet Evergreen forests

The tropical evergreen forest (west coast tropical evergreen forest) occurring within a narrow strip along the equator is perhaps the most endangered natural habitat. Extremely fragile, it has suffered most from human interaction. In species diversity it is the richest habitat and has developed in areas of the heaviest rainfall. There is very little soil erosion and that the streams and rivers originating from the rain forests are perennial. This may be attributed to the thick canopy and closely packed trees. In fact, scarcity of water is rarely felt. The evapo-transpiration from these forests is much higher than that from any other surface. This cools the atmosphere helping easy condensation of water vapor. This is the origin of the local summer rains. Tropical evergreen forests constitute the climax vegetation of Kerala characterized by at least three tiers, the highest often attaining a height of 40-45m. Many species develop plank buttresses. The middle stratum is more or less candle shaped and the lower characteristically conical.

The trees are heavily infested with epiphytic orchids, aroids, mosses, and ferns. Buttressing and fluting are common. This type is the most important vegetation seen between 600 m and 1100 m. Under favorable conditions like availability of proper shelter and moisture, it extends to an elevation of 1200 m above MSL. Evergreen formations occur at locations where annual rainfall of more than 2000 mm, temperature between 15°-30°C and humidity between 70 -100% The upper storey consists of chiefly Artocarpus heterophyllus, Bischofia javanica, Calophyllum elatum, Canarium strictum, Cullenia exarillata, Drypetes elata, Dysoxylum malabaricum, Elaeocarpus tuberculatus, Holigarna arnottiana, H. grahamii, Mesua ferrea, Palaquium ellipticum, Persea macrantha; Poeciloneuron indicum, Polyalthia coffeoides and Vateria Indica. The second storey is characterized by species such as Aglaia elaeagnoidea, Actinodaphne hookeri, Baccaurea courtallensis, Cinnamomum malabaricum, Dimocarpus longan, Elaeocarpus serratus, Garcinia morella, Gomphandra polymorpha, Litsea wightiana, Meliosma pinnata, Myristica dactyloides and Oreocnide integrifolia. They attain a height of 15 to 30 m.

The third storey which is less than 15 m in height consists of small trees like Agrostistachys meeboldii, Euonymus angulatus, Syzygium munroii, Syzygium laetum, Memecylon sisparense, Turpinia malabarica, Xanthophyllum flavescens and also profuse growth of shrubs like Dendrocnide sinuata, Lasianthus sp., Flemingia sp., Psychotria sp., Sarcococca brevifolia, Solanum surattense, Strobilanthes sp., Thottea siliquosa and many others. Monocot species are only a few having localised presence. Important among them are Arenga wightii, Calamus gamblei, C. thwaitesii, Pandanus furcatus, Pinanga dicksonii, Ochlandra travancorica, 0. rheedii, Oxytenanthera sp. Ground flora is composed of herbs like Elettaria cardamomum, Amorphophallus sp., Hackeria sp., some ferns and so on. Climbers like Pothos scandens, Piper (many species), Caesalpinia bonduc, Smilax sp. etc. are common. Wet evergreen forests are storehouse of medicinal plants (about 180 species) and many wild relatives of cultivated plants. About 25% of the forests of Kerala belong to this category. Forests of Silent Valley national park and Periyar tiger reserve represents some of the richest blocks of rain forests in Kerala.More than 50% of this forest has been subjected to timber working of varying intensity under selection felling system.

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