Present Status of Orchid Species Diversity Resources and Distribution in Dibrugarh District of Assam of North East India

Present paper deals with the present status of Orchid diversity resources in Dibrugarh District of Assam of North East India. A total of 113 Orchid species under 50 genera have been recorded from the regions. Of them, 29 species with 17 genera are terrestrial and the rest 84 species with 33 genera are epiphytic. This attempt is the first step to correct taxonomic identification and assessment to workout currently accepted botanical names, Voucher specimen, habitat, phenology and locality of Orchid species occurring in Dibrugarh District of Assam of North East India.


Introduction
Orchids belong to the family Orchidaceae is considered to be the most highly evolved in the floral specialization and diversified form among the monocotyledons. In India, Orchids from 9% of our flora and are the largest and highly advanced botanical family of higher plants. It is estimated that at about 25,000-35,000 species with 800-1,000 genera are distributed throughout the world. About 1331 species with 184 genera of Orchid species are found in India with temperate Himalayas as their natural home. North-East India constitutes an orchid hotspot, with nearly 70 percent of the total Orchids found in India are found in this region [1] and Assam is the second largest state of North East India and is a rich storehouse of Indian Orchids. The forests of Assam possess a large number of beautiful important Orchids. The total number of Orchid species may be around 193 under 71 genera out of which 27 are endemics.

Study Area
Dibrugarh District is located in the eastern part of upper Assam with an area of 3381 sq. km. The district extends from 27˚5´ N to 27˚42´ N latitude and 94˚33´ E to 95˚29´ E longitude. It is bounded by Dhemaji district on the north, Sivasagar district on the south and south east, Tinsukia district on the east and Lakhimpur district on the west. The area stretches from the North bank of the mighty Brahmaputra, which flows for a length of 95 km. Through the northern part of the district in the Patkai foothills in the south. At the foothills the altitude is 200m MSL and the Burhidihing river bank is 99m MSL (Fig. 1). In Dibrugarh district, the total area under forest is 217941.648 hectares, according to the forest department. There are five reserve forests in the district, namely Joypore-10876.68 hectares, Jokai-1848.01 hectares, Namdang-1858.63 hectares, Telpani-1332.288 hectares and Dihingmukh-5879.04 hectares.
Jokai, Namdang, Telpani and Dihingmukh are mixed forest with evergreen patches, types are 3/152 and 4D/SSI [2] Dibrugarh District of Assam of North East India Joypur Reserve forest forms a part of the world heritage of tropical/sub-tropical wet evergreen forest, classified as 1B/CI, multistoried in structure and rich in biodiversity, more popularly known as 'Rain forest' (Fig. 2). The forest is rich in biodiversity and one of the greatest reservoirs of Orchid germplasm due to its high rainfall, relative humidity etc. All these forests are close to the bank of river Buridihing or touching it.

Climate
Dibrugarh District has a unique photographic element, the area experiences subtropical monsoon climate with mild winters, warm and humid summer. The maximum rainfall is in summer (2740mm-3640mm) and the minimum rainfall is during winter (430mm-700mm). The maximum temperature ranges between 33℃ to 37℃ and minimum temperature between 8℃ to 10℃.
The climate can be classified into four seasons of the year, a. Winter: From November to January. The maximum temperature ranges between 27℃ to 29℃ and the minimum temperature between 8℃ to 10℃.
b. Pre-Monsoon: From March to May constitute this season. Temperature start raising, which ranges between 28℃ to 32℃.
c. Monsoon: From June to August constitute this season. The maximum temperature ranges between 33℃ to 37℃. Maximum rainfall recorded at its peak is 3000mm. d. Retreating monsoon: From the last week of September or the first week of October the monsoon starts retreating until winter arrives.
Thus the cycle repeats year after year.

Materials and Method
The intensive field survey works were carried out during 2006 -2011 covering all the seasons of the year in all parts of Dibrugarh district of Assam including floral nurseries, floral farms and forest areas. Collected Orchid specimens were made into standard mounted herbarium sheets following the procedure of [3]. The authors have done photographs and sketch the available Orchid species from the region. The relevant data from the field notebooks were then transferred to the labels of the herbarium sheets and computer. Normally, 2-3 specimens of each species in flowering or fruiting stage were collected and life form photographs were prepared. The specimens were identified, described and nomenclature checked with the help of the genera and species of Orchidaceous plants [4]; Folia Orchidacea [5]; Contributions to the Orchidology of India-I [6]; Contributions to the Orchidology of India-II [7]; The orchids of the Sikkim Himalayas [8]; Orchids of India-II: Biodiversity and Status of Bulbophyllum [9]; A Guide to the Orchid of Sikkim [10]; The Orchids of Thailand [11]; The Orchid Flora of North-West Himalaya [12]; Notes on Cirrhopetalum [13]; Indian Orchids Guide to Identification and Culture [14]; Indian Orchids Guide to Identification and Culture [15]; Orchids of Mussoorie [16]; Orchids of Arunachal Pradesh [17]; Flora of British India [18]; Orchids of Kumaun Himalaya [19]; The Orchids of Indo-China [21]; A Catalogue of Indian Orchids [21]; Orchids of Nagaland [22]; Contribution to the Orchid flora of Thailand [23]; Orchidaceae of Arunachal Pradesh [24]; Orchid Flora of Arunachal Pradesh [25]; 100 Sikkim Himalayan Orchids [26]; Assam's Flora [27]; Orchids of India [28] and specimens authentication done in CAL, Botanical Survey of India, Howrah, India. Specimens were identified with the help of literature and matched at the herbarium of department of Botany Guwahati University and BSI Shillong (Assam herbarium). Finally all the Voucher specimens have been deposited in the Botany department herbarium of Guwahati University. All the species were arranged systematically with botanical names, habitat, local distribution and flowering month. For ecological status, plot of 5mx5m quadrates for terrestrial and 10mx10m quadrates for epiphytic species was laid down diagonally in the field.
Habitat: Epiphytic in riverine forest and in secondary evergreen forest,  Gard. Chron. 710. 1869;Chowdhery, Orch. Fl. Arunachal Prad., 256, 1998;Mishra, Orch. India, 290, 2007. Flowers 4-5 cm 30: 149. 1859;Hook. f. Fl. Brit. India 5: 725. 1890;Chowdhry, Orch. Fl. Arunachal Prad. 193. 1998 natural habitat. Nevertheless, whole Orchidaceous family facing high risk of threat because of regular and rapid destruction of natural habitat by deforestation, upper layer soil erosion, overgrazing, effects of herbicides which is harmful for many saprophytic and terrestrial species and increase of agricultural lands by clearing forest, developmental schemes, rapid urbanization, ignorance and finally indiscriminate collection for floral business cause greater harm in the natural population of the species in the regions. Many species are in rare, vulnerable, threatened, endangered and critically endangered in the region. It is observed that high risk of extinction is possible in the near future if habitat of these species are not conserved in proper ways. Therefore, conservation of natural habitat is urgently necessary by means of conduction village level awareness programs by government departments and NGOs with constant affiliation with department of forest and wildlife in the regions is the only solution to save our praiseworthy Orchid diversity resources of Dibrugarh district is vanish for ever from nature.