Preserving Southern Indian Pteridophytes
Volume 2 Number 3 - May 1994
Like pollinating insects, humans seem to be impressed by flowering plants. Whatever the reason for this, the ferns and their allies have too often been neglected by botanists and lay-persons alike. Nevertheless, merely in terms of their numbers, more than 12,000 species, this group needs to be considered if we want to understand the ecology of our world. As well as their aesthetic or economic value, their antiquity and cosmopolitan distribution makes them a fundamental element of the biosphere. Pteridophytes play a vital role in tropical ecosystems, particularly in the rainforests, where it is estimated that 65% of them occur.
India has a wealth of pteridophytes, with some 900 species of ferns, together with 85 species of clubmoss and several other fern allies. Most occur either in the Himalaya or in the Western and Eastern Ghats of southern India. The World Conservation Monitoring Centre lists 82 pteridophyte species as threatened, or in some cases extinct, in India.
The Pteridophyte Flora of the Western Ghats
Most of the southern Indian pteridophytes are found in the Western Ghats. These mountains, the principal geographical feature of southern India, extend 1,400 km along the west coast, about 50 km inland. They rise steeply to an average altitude of 900 m (reaching up to 2,600 m) . Like the rest of India, the region has a monsoon climate dominated by the south-west and north-east monsoon winds. The annual rainfall is 2,000 - 6,000 mm, with the western slopes receiving the greatest precipitation. The rugged terrain and abundant rainfall support a diverse and unique flora.
Because of the region's geographical isolation, with the sea on three sides and a vast arid area to the north, the flora of southern India has a high level of endemism. This is less pronounced amongst the pteridophytes, although recent studies have shown that about 18% of the approximately 270 fern species found in southern India are endemic to the region.
The shade- and moisture-loving pteridophytes thrive between 700 and 2,000 m altitude, their altitudinal range directly related to the amount of precipitation. Thus, a species which will grow only at an altitude of, say, 1,300 m with an annual precipitation of 1,000 mm, will occur at much lower altitudes if rainfall increases. Epiphytes prefer high altitude forests and only robust species like Drynaria quelsifolia will be found at lower levels. About a third of the southeren Indian fern species are epiphytic or epilithic; the rest are terrestrial. Two thirds of the lycopods are epiphytic or epilithic; half of the Selaginella species are terrestrial and half are epiphytic or epilithic, Equisetum, Isoetes and a few ferns grow in aquatic habitats or marshes.
It is therefore apparent that these plants grow in varied habitats, and although they are generally more adaptable than tropical angiosperms, many species are still restricted to certain environments. About 23% of the species have a wide altitudinal range, whereas the rest are restricted to certain elevations. This proportion also applies to the light requirements of these plants, around 75% of the species being either sun- or sun-loving and about 25% found in both shady and sunny sites.
The epiphytes and more than two thirds of the terrestrial species grow in forests, which with wetlands are the most threatened ecosystems of the region. India's 2.7% annual rate of deforestation is among the highest on earth. New roads, the timber industry, hydro-electric projects, settlement schemes and population pressure put the few remaining forest areas in a precarious situation. Only about 5% of the southern Indian mountains still have intact forests and even these are partially tampered with by man. A recent survey, which enumerates 252 species and varieties of pteridophyte in the region, lists 90 as rare and many others as only locally common. With so small an area remaining under forest cover and the threat of further deforestation, about half of the pteridophyte species of southern India can be regarded as either vulnerable, threatened or endangered.
The Fern Collection of the Gurukula Botanical Sanctuary
The ex situ conservation of southern Indian pteridophytes has for more than a decade been a main concern of the Gurukula Botanical Sanctuary. The site of the garden, at an average elevation of 750 m, with a climate of high humidity and rainfall, and its proximity to a large tract of rainforest, provides an excellent environment for the cultivation of pteridophytes.
The fernarium of the Sanctuary is set out according to the ecological requirements of the plants, with special consideration being given to light requirements. There is one section for light-demanding species, another for shade-dwelling species and a third for species that prefer intermediate conditions. Intrasectional structures provide room for epiphytic, terrestrial and aquatic species, and each section has greenhouses and mist-chambers for the very tender and difficult species and for the acclimatization of new accessions. The sections are divided into nurseries, where studies on the horticultural requirements of species and small-scale propagation are carried out, and field gene banks, where cultivation and propagation take place on a large scale.
At the time of collection from the wild, extensive ecological data are recorded. These data will later form the basis for the layout of the field gene banks and the cultivation regime for each species.
Although the Gurukula Botanical Sanctuary concentrates almost exclusively on conservation, we consider it important to keep the garden open to the public and to offer them an insight into the state of the environment, the threats it faces and measures taken towards its preservation. Visitors can enjoy the garden just for its aesthetic setting and also for the educational value of the exhibits, backed up by interpretative labels and boards. Researchers and scientists use the facilities of the Sanctuary, which include a library, nurseries, gene banks, plant records, access to the forest. The nursery provides ornamental plants, including robust species of pteridophytes, free of charge to the interested visitor. Guided group tours are also arranged.
Far from being insignificant, pteridophytes play an important role in nearly all the world's ecosystems. It is time that their status be recognized, and that we give them the attention and protection they deserve as indispensable members of organism Earth.