INTRODUCTION

Silent Valley is a small stretch of land consisting of about 8952 hectares of forest with diverse vegetation types. It harbours about 2000 plant species which include over 1000 species of flowering plants that belong to 561 genera and 136 families (Manilal, 1988), 100 fern and fern allies, 200 liverworts, 100 mosses, 325 fungi, 75 lichens and about 200 algae (Vohra et ai., 1982). Orchidaceae is the largest family represented by 107 species in 54 genera followed by Poaceae with 56 species in 32 genera, Fabaceae by 55 species in 26 genera, Rubiaceae by 49 species in 27 genera and Asteraceae by 49 species in 25 genera. This is quite characteristic of South India. The gymnosperm flora is very poor and it is represented by two species only viz., Cycas circinalis and Gnetum uia belonging to two families, Cycadaceae and Gnetaceae, respectively. From a single expedition to Silent Valley Vohra et ai. (1982) recorded 78 species of pteridophytes including a new species of Pteris. Nayar (1980) recorded 89 taxa of ferns and nine fern allies from the non-submergible area and 76 taxa of ferns and seven fern allies from the submergible area of the proposed dam in Silent Valley. Nayar et al. (1985) later discovered a new genus Nistarika belonging to Polypodiaceae besides many new species of ferns from Silent Valley. Bryophytes of Silent Valley have not been sufficiently studied. Of about 728 taxa of liverworts known from India about 225 species are found in South India. Vohra et al. (1982) reported 83 species of mosses from Silent Valley including three new species and four new additions to South India. The discovery of the Chinese Handeliobryum setschwanicum in fructification from Silent Valley is believed to be an important evidence for the pristine nature of the area (Vohra et al., 1982). Algal flora of Silent Valley remains almost untouched. Fungal flora is insufficiently known. Microfiora is totally unknown. Vohra et al. (1982) recorded 77 species of lichens from Silent Valley including II new additions to India.

The flora of Silent Valley offers immense scope for novel sources of food, fodder, fibre, medicine, perfumery, cosmetics, gum, resin, dye, tannin and timber. Their potential has to be tapped to meet the changing and increasing demands of mankind.

MEDICINAL AND AROMATIC PLANTS

It is estimated that nearly 4/5th of the drugs available in various pharmacopeias and 2/3rd of the important spices and perfume yielding plants used the world over are available in their natural state in India (Pushpangadan, 1990). About 50 percent of the 45,000 plant species recorded from India have medicinal and aromatic value. Many members of the flowering plant families like Acanthaceae, Aizoaceae, Alangiaceae, Apocynaceae, Araceae, Aristolochiaceae, Asclepiadaceae, Asteraceae, Berberidaceae, Caesalpiniaceae, Combretaceae, Convolvulaceae, Dioscoreaceae, Ericaceae, Euphorbiaceae, Flacourtiaceae, Gentianaceae, Lamiaceae, Lauraceae, Liliaceae, Lobeliaceae, Lythraceae, Malvaceae, Meliaceae, Menispermaceae, Myrsinaceae, Myrtaceae, Papilionaceae, Periplocaceae, Piperaceae, Poaceae, Polygonaceae, Ranunculaceae, Rutaceae, Santalaceae, Sapotaceae, Solanaceae, Sterculiaceae, Symplocaceae, Zingiberaceae, Zygophyllaceae etc. are medicinally very important. The medicinal and aromatic plant diversity in Silent Valley is not limited to the plurality of species alone but also includes wide intraspecific genetic diversity. Traditionally most of the plants of this category are harvested from lowland forests like moist deciduous or dry deciduous forests.

Ethnobotanical investigations carried out under the All India Coordinated Research Project on Ethnobiology (AICRPE) reported over 800 plant species used for medicinal purpose by different tribes and other local communities (Pushpangadan, 1990). The tribes of Attappady viz., the Irulas, Kurumbas and Mudugars have been utilizing the plants of the neighbourhood areas of Silent Valley. They are comparatively dry areas. These tribes are also utili sing many plants of Silent Valley. The medicinal value of many species occurring in high altitude evergreen forests is still not sufficiently known. Artemisia nilagirica (Clarke) Pamp., Buddleja asiatica Lour., Cyclea barbata Miers., Iphigenia indica (L.) A. Gray ex Kunth, Rubia cordifoUa L. and are well known medicinal plants available in Silent Valley. A detailed chemical investigation of the medicinal plants of Silent Valley, if undertaken, would be interesting and highly rewarding.

ORNAMENTAL SPECIES

Apart from the orchids I Silent Valley has. a rich assemblage of promising ornamental plants. This is an untapped resource which can be sustainably utilised. Genera like Aeschynanthus (one var.), Arisaema (eight spp.), Begonia (two spp.), Didymocarpus (two spp.), Exacum (three spp.), Globba (two spp.), Gymnostachyum (one sp.), Hedychium (three spp.), Hoya (two spp.), Impatiens (nine spp.), Jasminum (five spp.), Lilium (one var.), Medinilla (two spp.), Rhyncoglossum (one sp.), Sonerila (five spp.), Strobilanthes (twelve spp.), Thunbergia (three spp.) etc. have beautiful flowers. These taxa are worthy of introduction as garden plants. Many species of Impatiens, Strobilanthes and Thunbergia are particularly promising.

LESSER KNOWN EDIBLES

A recent study conducted at TBGRI on the lesser known edible fruit yielding plants of the Western Ghats yielded interesting results. As part of the project work we undertook several exploratory surveys in Silent Valley and collected many lesser known edible fruit yielding plants. Baccaurea (one sp.), CucumeZZa (one sp.), Cucumis (one sp.), Elaeocarpus (four spp.), Garcinia (three spp.), Mangifera (one sp.), Rubus (four spp.), Spondias (one sp.), Syzygium (ten spp.) etc. have promising edible fruits.

WILD RELATIVES OF DOMESTICATED CROPS

Wild relatives of many of the cultivated crops such as. Alpinia, Amomum, Atylosia, Cinnamomum, Curcuma, Dioscorea, Elettaria, Garcinia, Mangifera, Musa, Myristica, Panicum, Piper, Rauvolfia, Zingiber etc. are available in plenty in Silent Valley. Every allele of this gene pool is very valuable as it can substantially contribute to future crop improvement. The genetic library that gets opened before us may have immense potential in fighting maladies that may afflict crops in future.

RESINS

Species such as Vateria indica L., Canarium strictum Roxb., Sterculia guttata Roxb. etc. yield resins that can be commercially utilized. These three species are frequently found in Silent Valley.

ENDEMIC PLANTS

As mentioned above, there is a high degree of endemism in flowering plants of Silent Valley. About 30 percent of the plants recorded from here are either endemic to peninsular India or South India.

NOVELTIES

Twenty five taxa of flowering plants are discovered from Silent Valley as new to science.2 Another fifteen species collected from Silent Valley constitute additions either to the Flora of Kerala, south India or India.

STRATEGIES FOR CONSERVATION

Being a National Park, Silent Valley seems well protected from constant disturbance. The old bridle paths and the roads that lie scattered in the valley are now being invaded by secondary species and are blocked by them at some points. The grasslands at three areas flourish with their unique grass genus Silentvalleya and its associated orchid Ipsea malabarica. The protection given to Silent Valley is to be further strengthened at points like Walakkad, Neelikkal and Aruvanpara so that any infiltration can safely be avoided. In situ conservation stands out as the best means of conservation as it does not hamper evolution. In the ex situ front representative samples can be cultivated in Botanic Gardens. An exclusive conservatory for Silent Valley plants at Mukkali could be of great educational value. This ex situ plot could be developed as a display and education centre so that visitors can be properly briefed on the value of different categories of plants before taking them to the field.

EFFORTS AT TBGRI

As part of the National Gene Bank established at Tropical Botanic Garden and Research Institute (TBGRI), we maintain the genetic diversity of over 100 medicinal plants of Peninsular India, which include many species from Silent Valley. As part of the long term monitoring programme, we, at present, study populations of Arisaema and the keystone species Cullenia exarillata at Silent Valley. The autecology and conservation biology of many species, particularly the rare and endemic ones have been initiated by scientists of TBGRI. The study of the reproductive biology of the Malabar Daffodil Orchid (Ipsea malabarica), of Silent Valley has yielded interesting results. Most of the orchids of Silent Valley are represented in the TBGRI Orchidarium. We have successfully produced a new hybrid between Ipsea malabarica and Spathoglottis plicata. To popularise this showy species we are at present multiplying them through tissue culture.

CONCLUSION

The Western Ghats has been designated as one of the 18 Hot Spots of the world and one of the two in India on account of the high degree of endemism and constant threat to flora and fauna (Myers, 1990). This mountain chain which was once a continuous forest tract has lost its continuity at several points. The rich assemblages of plants that are found quite isolated on this mountain at distant regions represent their last refugia. Silent Valley and the adjoining forests that spread across the state boundaries of Kerala and Tamil Nadu fOfm one such refugium for many a species. We have to save it at any cost for posterity.