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Taxonomic and phytogeographical studies on the flora of Mirik and its environs in Darjeeling district
(University of North Bengal, 1987) Mukhopadhyay, Chittaranjan; Basu, P. K.; Ghosh, R. B.
In recent years much attention has been given to Mirik to establish it a beautiful hill resort in connection with the development of tourism in the region. It is situated at an altitude of 170Dm with its own special charm, located at 49 km from Darjeeling and 52 km .from Siliguri. This hill resort has a special attraction for having a magnificent lake fed by perennial streams. It is under the Mirik P.S.of Darjeeling district in West Bengal and is located between 26°47'N. lat. and 26°55'N. lat., 88°8'E. long. and 88°15'E. long. It claims its special identity in respect of its strategic position in the Sub-Himalayan hilly tract in the northern region of West Bengal. Its flora is significant from the scientific, cultural and utilitarian view points. It has a wide range of habitats which provide ecological diversity. Phytogeographicall y also it occupies a key position. The economy of Mirik and its environs is primarily based on agriculture, forestry and plantation. Like all other parts of the world, the ecosystem of the region has also been observed to be the most gravely threatened now-a-days. Due to large sc.ale destruction without adequate replacement of forest trees, forest wealth has been diminished and due to Jack of plant cover, soil is subjected to the combined influence of erosion, leaching, insolation and radiation. Thereby, much of the normal biogeochemical cyde is. lost causing Jack of regeneration of forest plants. Recently, due to policy at the National level, large scale plantation is being encouraged in connection with Eco-Development Programme. But the proper management of the forest in a region is possible only with the utilization of the local plants in the area. It is, therefore, of primary importance to understand the. present day plant resources of the region. As lhe development and distribution of floristic elements are very much dependent on the ecological condition of a particular region, emphasis has been given to study the floristic composition, ecological conditi'on of the . re_gion with special ~tress on the behaviour of different plant species from phytogeographical point of view. During investigation some ecological observations on Mirik and its environs have been made after accumulation of information from various sources. In this connection collaboration has been made with the National Atlas and Thematic Mapping Organisation, Government of India. Information so far represented in connection with Mirik P. S. may be considered for the first time to report in this .field of work. During the preparation of / topographic section, it has been noted that less than 700m elevation shows the- lower erosional surface, 700-1000m the middle erosional surface and above 1 DOOm represents upper erosional surface of the mountains. Mirik itself lies in the. highest part of the region in Mirik P.S. The height gradually slopes down towards south-east havi~g average height of 300-600m above sea level. The surface configuration of this area undoubtedly presents a complex physical environment due to. different Geomorphic processes. The study on drainage and the river system of the region has. specially been emphasized due to the fact that now-a-days catchment area has been noted to be a very important from ecological point of view. In co-nnection with the study on this aspect, it has beeri noted that the Mechi and the Balason are the two main rivers with a large number of tributaries and branches, the courses of which have been taken into consideration during the preparation of map. The central part of the region acts as main water divide line. The water divide area is having a slope of less than 20% as calculated from the relief and the slope is maximum where lhe land is merging with the boundary rivers. Thus along both the rivers, the Mechi and the Balason, the slope increases to more than 50%. Five different zones of soil have been prepared for Mirik P.S. These are Red Podosol, distributed in the northern part of the region, Brown Earth, represent)ng the major part of the area, Ash Grey Soil with association of Red Soil, representing a narrow-strip towards the southern part, Whitish Grey Soil adjacent to the previous one in southern direction and Grey Soil with association of yellowish brown Soil representing the extreme southern part of the police station. Out of the study on the earlier records on climatic factors, it has been noted that since 1 Q50 the rainfall has been gradually declining from 3477.51 mm (1850-1855) to 2560.00 mm (1982-1987). Total rainfall in the year of 1988 has been observed to be 2039.4 mm. Thus the vegetation, now-a-days, is beinc:J subjected to stressed condition as compared to earlier days. Due to rapid growth of urbanisation, the growth of human population has been observed to be at increased state and for this reason biotic influence on vegetation is inevitable. This "increase in population coupled with the increased demand on natural forest areas for cultivation of cereals for food and for fuel, forest areas are being destroyed at a greater pace, year after year. Similarly, increased communication even with remote villages facilitates more movement of people from outside along with their domestic animals and consequently more interference with the vegetation. The major part of this area has been noted to have population density of 1-3 persons/ha. The small area of the central part has more than 9 persons/ha, and a small area in the north has.been observed to cover less than 1 person/ha. A very significant feature observed here in the study of landuse is the extensive existence af tea gardens. Crop land occupies a very little area which is distributed mostly in the northern part of the region. A map has been prepared to represent rural settlements, forests, scrubs and wastelands. · The primary or vergin forest has been noted to become restricted in the region. Majority of forest patches are secondary in nature. Vegetation of this area has been classified on the basis of physiognomy and structural features of the plant in relation to "the altitude of the hill and climatic conditions, specially the rainfall. Four vegetational zones i.e. Tropical Deciduous Sal Forests (Plantations; 1 00-500m), Tropical Evergreen (500-1200m), Subtropical Evergreen (1200-1800m) and Temperate Mixed Zone (1800-2630m) have been marked out and different plant species in various zones of the primary forests have been worked out. A change of vegetational structure for secondary forest formation due to the influence of various factors have been noted. Different species available in different zones of primary and secondary forests have been enumerated. Water reservoirs in different zones of Tropical, Subtropical and Temperate regions have been observed though typical aquatic vegetation is poorly developed, the marshland vegetation has been studied in details. Cultivated and other useful plants with special reference to food, medicinal and ornamental value available in the region have also been recorded. Special emphasis has been given on the survey of various plant materials used by the local tribes/hill people. Besides, common trees yielding timber, fibre and fruits have been identified. In connection with the taxonomic study on the flora of Mirik and· its environs in Darjeeling district, much emphasis •has been laid upon the collection of plants, preparation of herbarium sheets and identification of them after ·consultation with different herbarium sections available. Nomenclatu' re and citation, short description, flowering and fruiting periods, local name, if any, notes on the frequency of distribution, plant association, economic use, if any, of 1059 taxa including 71 cultigens of Angiosperms and G~n;nosperms have been taken into consideration. Out of which again 987 and 67 species of Angiosperms are represented as wild ~nd cultigens respectively. Gymnospermous taxa have been found to be represented by Cryptomeria japonica (L. f.) D. Don in wild state and 4 other cultigens. The system of Bentham and Hooker (1862-1883) with. some modifications based on recent knowledge has been· followed during the representation of the sequence of families in the flora. Monocots include 300 species (excluding the cultivated 11 species) unde·r 136 genera and. 14 families. Similarly, Dicots cover 687 species (excluding the cultivated 56 species) under 350 genera and 95 families. "Based on total number of collection (excluding cultigens), percentage occ:urrence of family, genera and species of Dicots have been observed to be 86.36%, 71.87% and .69.53% respectively; Similarly, in Mof\OCots, family, genera and species have been represented by 12.73%, 27.93% and 30.36% respectively. The approximate ratios between the family, genus and species of the Angiosperms have been worked· out. The Monocot-Dicot ratios in terms of family, genus and species have been calculated to be 1:6.8, 1:2.6 and 1:2.3 respectively. The genus-species ratio for the Angiosperms is 1:2 approximately. Twenty ·different families in order of dominance have been worked out on the basis of the number of taxa incorporated in each family. Orchidaceae has been noted to include maximum of 131 taxa under 41 genera. On the other hand, each of Apiaceae and Acanthaceae includes minimum of 13 ta?