Emerald citadel - a coffee table book on the rainforests of the Western Ghats
June 22 is World Rainforest Day (worldrainforest.org
). On this occasion, we recall our publication "Emerald citadel - a coffee table book on the rainforests of the Western Ghats". Here is an extract from the book.
Rain forests are formations with lush green and evergreen canopy irrespective of the season. Wet evergreen forests develop in tropical regions that are extremely wet and humid. Evapotranspiration from these forests is much higher than that is known from any other surface. This cools the atmosphere and condensation of water vapour follows. This ensures regular local summer showers. As a result, most streams and rivers originating from the rain forests tend to be perennial. In fact, scarcity of water is rarely felt in a rainforest.
Evergreen forests occur where annual rainfall is more than 2000 mm, temperature between 15°-30°C and humidity range is between 70 and 100%. In Kerala, wet evergreen forests are seen between 600 m and 1100 m above sea level. However, When conditions are favourable evergreen forests are formed up to an elevation of 2000 m in altitude.
Tropical evergreen forests are characterized by at least three tiers, the highest often attaining a height of 40-45m. As it has various layers and diverse life forms, there is very little soil erosion and nutrient loss. Trees usually have a heavy epiphytic load of orchids, aroids, mosses, and ferns. Formation of buttress roots and fluting of boles are common.
As the species composition of the same type of forests varies from one site to another, let us look at the most probable combination.
The upper storey has tall trees such as 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 macrocarpa.
The second or middle storey have medium sized trees attain a height of 15 to 30 m such as Aglaia elaeagnoidea, Actinodaphne hookeri, Baccaurea courtallensis, Cinnamomum malabathrum, Democarpus longan, Elaeocarpus serratus, Garcinia morella, Gomphandra polymorpha, Litsea wightiana, Meliosma pinnata, Myristica dactyloides and Oreocnide integrifolia.
The third storey which is below 15 m in height consists of small trees such as Agrostistachys meeboldii, Euonymus angulatus, Jambosa munroji, J. laeta, Memecylon sisparense, Turpinia malabarica, Xanthophyllum flavescens and also profuse growth of shrubs like Dendrocnide sinuata, Lasianthus sp., Moghania sp., Psychotria sp., Sarcococca brevifolia, Solanum surattense, Strobilanthes sp., Thottia siliquosa and many others.
Monocot species are only a few having a very localised presence. Important among them are Arenga wightii, Calamus gamblei, C. thwaitesii, Pandanus furcatus, Pinanga dicksonii, Ochlandra travancorica, O. rheedii, Oxytenanthera sp.
Ground flora of the evergreen forests vary widely according to altitude and is composed of herbs such as Elettaria cardamomum, Amorphophallus sp., Heckeria sp., some ferns. Climbers like Pothos scandens, Piper (many species), Caesalpinia bonduc, Smilax sp. etc. are common.
Wet evergreen forests are a rich abode 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 represent some of Kerala's richest blocks of rain forests.
Published on: June 22, 2021
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