Bio-geographically Arunachal pradesh is situated in the Eastern Himalayan province, the richest biogeographical province of the Himalayan zone. The entire territory forms a complex hill system with varying elevations ranging from 50m in the foot-hills and gradually ascending to about 7000m, traversed throughout by a number of rivers and rivulets. Apart from large number of timber species, there are innumerable varieties and kinds of orchids, medicinal plants, ferns, bamboos, canes, wild relative of large number of our cultivated plants, and even plants of biological curiosities, such as parasites, saprophytes, etc. are found. Other important group of plants are Rhododendrons, Hedychiums and oaks etc.
Orchids form a dominant group of plants with their attractive and unique blooms. There are more than 600 species of orchids, 52 species of rhododendron, 18 species of hedychium, 16 species of oak, 18 species of canes, 45 species of bamboo in addition to large number of medicinal and aromatic plants.Arunachal Pradesh has many species of endangered, endemic, primitive, and relict flora, Magnolia Pterocarpa pterocarpa is one such primitive angiosperm, which occurs in the foot-hills. Some rare and endangered flora that occur in Arunachal Pradesh are: Amentotazus assamica in Lohit District . Rhododendron arunachalense found in Subansiri District, Rhododendron dalhousie, and Tetracentron sinense, occurring in Kameng District, Rhododendron santapaul recorded in Subansiri District.
Gomphogyne macrocarpa found in Tirap and Kameng Districts, Gymnocladus assamicus and Lithocarpus Kamengensis available in Kameng district. Rhynchoglossum lasulinum in kameng and Subansiri District. Dendrocalamus sahni in Subansiri District. Hypericum griffitthii in Kameng District, Coptis teeta of Dibang Valley Districts, etc. The State harbours about 52 species of of Rhododendrons, 18 species of Hedychium , 16 species of Qaks, 33 species of Coniters and a large number of fems and lichens.
About 500 species of orchids occur in Arunachal Pradesh. These include about 140 species of terrestrial orchids with 15 saprophytes and about 340 epiphytes found in the different forest types. The prominent species are: Cymbidium ansifolium , C, grandiflorum, Coelogyne corymbosa. Dendroblum aphylla, D. fimbriatum var occulatum, D. densiflorum, Calanthe masuca, Phaius flavus, Paphiopedilum. Tairriearum, venustum renanthera imschootiana, vanda coenulea , etc. Rhynchostylis refusa is the state flower of Arunachal pradesh.
Types of forests in Arunachal pradesh
Arunachal Pradesh is a treasure trove of nature. It is one of the maximum forest cover state of India, Sixty one percent of its geographical area comprises forests. The forests are spread over an elevation of 100 m. in the foothill regions to 7,000 m in the Himalayas . Such an ecological diversity has naturally resulted in varying forest types. The tropical forests at the foothills up to the height of 1,000 m are of the wet evergreen variety as well as the tropical evergreen variety and the riverine semi green variety. Then there are the sub tropical forests 1,000-2,000 m), the pine forests 1,000-2,000 m) and the temperate forests 2,000-3,000m). There are both the broad-leafed temperate forests as well as the conifer forests. The bamboo forests and grasslands have not been enlisted so far.
Tropical forests :These forests occur up to an elevation of 900 metres above MSL . They are persent in all the districts along the foothills . These forests can further be classified into two main types viz. tropical evergreen forests and tropical semi evergreen forests.
Subtropical forests : This type of forests occur in districts between altitudes 800m to 1900m. These are essentially evergreen and dense in nature. The trees attain large dimensions (25-40m high). The forests are rich in species diversity and dominated by Fagaceae members. Castaniopsis lidica, C. armata, Quercus lamellose, Q. griffithili, Q. spicata, Q. Semiserrata, Q. fenestrala, Michelia ,Ulmus lancifolium, Engelhardia spicata, Ficus spp. Acer oblongum, Schima wallichji, S.khasiana, etc. are the dominant tree species. Luxurious growth of climbers, orchids & ferns, occurs in these forests.
Pine forests: These forests extend both in the subtropical and temperate belt in between 1000 m to 1800 m elevation. These are generally met with in rain shadow area and are represented by three different sepecsies viz. Pinus roxburghii, P. wallichiana and P.merkusii. Sub Tropical Pine Forest is found in Rupa and Dirang valley of Kameng district and forms either pure stands or occasionally mixed with P. wallichiana, Quercus spp, Prunus sp. Etc. P. wallichiana is widely distributed in Rupa, Dirang valley (Kameng district), Hapoli ( Lower Subansiri district), Mechuka (West Siang district), Anini (Dibang valley district). and Melinja ( Lohit district). In Kameng, Siang and Lower Subansiri district it is found in nearly pure stands or less frequently mixed with P. roxburghii, Quercus spp. Lyonia sp. Etc. In Dibang valley they are found in association with Betula alnoides, Alnus nepalensis, Lyona ovalifolia, etc. In Lohit district it is less extensive and is associated with Tsuga dimosa, Pinus merkusii, occurs in Lohit district along the Lohit valley extending from Kharang (Hawal) to Dichu.
Temperate forests: Occur in all districts of Arunachal pradesh as a continuous belt and can be divided into two subtypes viz. Temperate broad leaved forests and Temperate conifer forests.
Alpine forests : This type of vegetation occurs on the peaks of higher hills above an altitude of 4000 m upto 5500m above timber line. For major part of the year, the area is covered by snow and plant activity is restricted to a few months when snow melts. Alpine Vegetaion As a rule there are no tall trees but dwarf branches and shrubs and mainly herbs with deep roots and cushioned leaves and branches. The profusion of bright coloured flowers which is purely seasonal for a brief period makes the area highly attractive. Plans like Rhododendron nivale., R. anthopogon, R. thomsonii, Sedum sp.., Festuca sp.., Rhodiola sp,.. Saxifraga sp. Saussaurea sp,. Arenaria sp,. Rheum sp. etc. form the major constituent of this peculiar vegetation.
Bamboo Forests and Grasslands : Bamboo trees are seen throughout Arunachal Pradesh. They grow in pure stands with less associated species. Bamboos appear in areas abandoned after shifting cultivation. Bamboos of Arunachal Pradesh are Bambusa tulda, Pseudostachyum polymorphum, Cephalostachyum that occur in higher elevation between 1000m-2000m. Grasslands are found in plains and at higher elevations. It is maintained through recurring annual fires at higher elevation and excessive grazing at lower elevations. In lower elevation Saccharum spontaneum, Neyraudia reynaudiana, Chrysopogon aciculatus are the common grasslands that are visible.
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