When it was proposed to start a hydroelectric project in Silent Valley, the proposal generated debates not only about the matter of 'conservation' vis-a-vis 'development' in general, but also about the possible importance of biodiversity as well as the ecological status of Silent Valley forests in particular. Conservationists were of the opinion that the Silent Valley forests represented the only comparatively undisturbed patch of tropical evergreen rain forests in this part of India and that it harboured many new and rare species of plants and animals unknown to man, which might be lost for ever in the submerging waters and the ecological changes resulting due to the construction of the power plant. Many tropical plants are known to be very narrow in their geographical range, highly specific in their ecological requirements and are highly vulnerable to changes in their surroundings. Since many of these pl_nts were not catalogued, we would be losing them without even knowing that they existed.
Those who supported the construction of the dam and hydroelectric project, mainly on economic grounds, argued that the forest in Silent Valley could not be classified under the tropical evergreen rain forest category and that its flora and fauna did not contain any new or rare species which were not found elsewhere in the Western Ghats. They also published a 'Flora and Fauna' in support of their contention wherein it was categorically stated that" so far there is no record of any new or endangered species occurring in Silent Valley forests."
Since there was no thorough study on any major component of the flora or fauna of Silent Valley, a detailed four year long study on the angiosperm flora of the region was undertaken from 1981 to 1985. Results have already been published (Manilal, 1981, 1987, 1988, 1995, 1997; Manilal et al.,1983, 1985 a, 1985 b, 1988, 1989; Manilal and Sabu, 1984, 1985; Manilal and Sathish Kumar, 1983 a, 1983 b, 1983 c, 1984 a, 1984 b, 1984 c, 1984 d, 1984 e, 1984 f, 1985 a, 1985 b, 1985 c, 1985 d, 1986 a, 1986 b, 1991; Manilal and Suresh, 1985; Mathew et al., 1984; Sathish Kumar and Manilal, 1986, 1987).
Though it was reported earlier that there were only 240 species of angiosperms in Silent Valley with no new or rare species among them, during this study (Manilal, 1988) nearly 1,000 species belonging to 134 families could be found growing there. The area that would have been submerged under water in the event of construction of the dam was found to harbour 84 species which were not present anywhere else in the region. This included 23 rare or new species which would have been lost completely by the flooding waters of the dam.
New species of angiosperms collected from Silent Valley during the study are:
- Cucumella silentvalieyii Manilal, Sabu & P. Mathew
- Eria tiagii Manilal, Sathish & Wood
- Hydnocarpus pendulus Manilal, Sabu & Sivar.
- Robiquetia josephiana Manilal & Sathish
- Sauropus saksenianus Manilal, Prasa. & Sivar.
A large number of rare and endangered plants and many new records
for Indian and South Indian flora could be found thriving in Silent Valley including Cyciea barbata Miers, Dendrobium panduratum Lindl., Oberonia bicornis Lindl., O. tenuis Lindl., Scutellaria oblonga Benth., Syzygium makul Gaertn., S. neesianum Am. and so on.
Many species supposedly endemic to Sri Lanka and Philippines could be located in Silent Valley. Cyclea barbata Miers is a medicinal plant endemic to Philippines, but it was found in the area. The Sri Lankan endemic orchid, Dendrobium panduratum Lindl. which had not been collected even from its type locality in Sri Lanka since 1881, was flourishing at the Valiyaparathod area in Silent Valley. The ground orchid Ipsea malabarica (Reichb. f.) Hook. f., last collected in 1852 by Jerdon and considered as an extinct species, c01.lld be seen growing in sizable populations in Silent Valley during this study. Many wild relatives of Piper, Cinnamomum, Hydnocarpus, Syzygium, Myristica and such other spices and medicinal plants were growing abundantly there.
Contrary to the belief that peninsular India is very poor in its orchid wealth and only two or three dozens of them grow in Silent Valley forests, as many as 108 species of orchids could be collected from there including many species with large, showy and horticulturally exploitable flowers.
Epiphytes, climbers and lianas constitute about 22 percent of the total angiosperm flora of Silent Valley. The presence of these groups of plants in large numbers is considered an important characteristic feature of tropical evergreen rain forests. In the Amazon forests they constitute only about 18 percent of the flora, which is less than that in Silent Valley. The Silent Valley epiphytic orchids contain 12 species of rare Neottioids. As these Neottioids are highly sensitive to their surroundings, their presence in such a sizable number may be considered indicative of the undisturbed and ecologically safe nature of the habitat. Most of the other features that are commonly attributed to typical tropical evergreen rain for_sts such as a preponderance of woody vegetation, species with leaves in mesophyll size class, development of drip tips, development of buttresses by trees, tall trees with straight boles, unusually thin bark, surface root system, multi-layering of vegetation, evergreenness, strong tendency to change species composition in time and space, high diversity of dominance, etc. are all profusely exhibited by the plants of Silent Valley, thereby showing that the forests there truly belong to the typical tropical evergreen rain forest category.
Comparative studies on the density, frequency, reproduction and regenerative patterns of 12 dominant tree species of Silent Valley and adjacent Attappady reserve forests show that while Attappady forests are in a highly disturbed state, Silent Valley upland forests are undisturbed though Silent Valley riparian forests show the effects of slight disturbances.
Thus Silent Valley may be considered very rich in its biodiversity with many new, rare, interesting and important species. The forests in Silent Valley truly belong to the typical tropical evergreen rain forest category and are generally undisturbed, maintaining an ecological balance and equilibrium, thereby providing a haven to very rare and important native species.
Acknowledgement
The data presented in this paper were collected during the tenure of a research project on the Flora of Silent Valley funded by the Department of Science & Technology, Government of India from 1981 to 1985.
