SUMMARY
A three year study (from December 2011 to December 2014 and in June 2015) on butterflies covering four major forest sub-types as classified by H.G. Champion & S.K. Seth in 1968 in ‘Forest Types of India’, which occupy 60% of the forest area lying below 2,500m across Arunachal Pradesh State in the eastern Himalaya of India, revealed 415 taxa belonging to six families (Hesperiidae: 74 species of 42 genera; Papilionidae: 37 species of 10 genera; Pieridae: 36 species of 15 genera; Lycaenidae: 85 species of 49 genera; Riodinidae: 7 species of 3 genera & Nymphalidae: 176 species of 71 genera, respectively). These included many endemic and rare species typical of these forest sub-types, i.e., (i) 2B/1S1 Sub-Himalayan Light Alluvial Semi-Evergreen Forest (32 species), (ii) 2B/ C1(a) Assam Alluvial Plains Semi-Evergreen Forests (5 species), (iii) 2B/2S2 Eastern Alluvial Secondary Semi-Evergreen Forests- (15 species) and (iv) 3/1S2 (b) Terminalia-Duabanga (3 species), respectively. The relative number of species and individuals sampled were the highest at altitudes below 500m, and gradually declined as the altitude increased to 2,000m, and above 2,500m species richness declined sharply. The number of species and their relative abundance were the highest during July–August (Monsoon-first peak) and then again in November-December (Autumn-second peak), while the numbers were lowest during winter. These findings suggest that these four forest types are important both for the purpose of ecotourism as well as conservation of endemic and rare taxa found in the eastern Himalaya and northeastern India at altitudes below 2,000m. A complete list of all the taxa sampled is given along with relative abundance status during sampling, Indian Wildlife (Protection) Act, 1972 status, and distribution in different forest types in the state. Ten potential butterfly ecotourism zones are suggested for the state. Planning land-use for biodiversity conservation based on butterfly-forest type associations, by taking forest sub-types as units of conservation, is suggested as an option for the eastern Himalaya.