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The present study describes the structure, composition and regeneration of tree species in undisturbed and disturbed tropical forests in Bhuban hills in southern Assam, India. The study area is part of one of the globally recognized biodiversity hot spots and in spite of the increasing human activities in these forests, so far no information is available on their impacts on plant assemblages in the area. In each forest, the vegetation was analysed through 50 quadrats (10 m × 10 m) in a belt transect of 500 m × 10 m. A total of 49, 47 and 42 tree species were recorded in disturbed forests and 62, 61 and 60 species in undisturbed forests. The average tree density and basal area were significantly higher in undisturbed forests (708.67 and 42.01 m 2 ha −1 , respectively) than disturbed forests (443.33 and 18.44 m 2 ha −1 , respectively). The population structure of tree species in disturbed forests showed a fluctuating curve, and in undisturbed forests, it was a reversed J-shaped curve. The present study reveals that the species richness, diversity, density and basal area have significantly declined (P < 0.01) due to anthropogenic disturbances. As reflected from the population structure, most of the tree species in disturbed forests showed poor regeneration status. If degradation of these forests continues at the present pace, several of these species which are providing various ecosystem services to the local human communities may disappear in the very near future.

This study evaluated the ecosystem carbon (C) stock and sequestration potential for predominant land uses converted from forest in Northeast India to advance the scientific knowledge and minimize the anthropogenic C emissions from land use change (LUC). Field assessments were conducted on 6 predominant land uses including (a) natural forest (NF), (b) degraded forest (DF), (c) rubber (Hevea brasiliensis) plantation (RP), (d) Areca (Areca catechu) plantation (ArP), (e) pan (Piper betle) jhum (slash and mulching) agroforestry (PB), and (f) Imperata grassland (IG) of Northeast India to assess changes in ecosystem C stock with progressive and retrogressive LUC. Ecosystem C stock was the highest for NF (300.5 Mg ha À1) and the lowest under IG (110.4 Mg ha À1 ). The ecosystem C stock under PB and IG was 11% and 63%, respectively, lower than that under NF. In comparison with DF, the gain in ecosystem C was in the order PB (125%) > RP (99%) > ArP (4%). The ratio of soil organic carbon to ecosystem C stock was~50% for NF, PB, and RP and that shifted to~80% for ArP/DF/IG. The LUC and management of DF through PB and RP indicated the ecosystem C sequestration rate of 5 and 4 Mg ha À1 year À1, respectively. Similarly, the ecosystem C sequestration rate was 0.5 and 4 Mg ha À1 year À1 , respectively, when IG was converted into ArP and RP. Therefore, restoration of degraded lands (viz., DF and IG) through RP and PB enhanced ecosystem C sequestration rate and reduced CO 2 emissions from LUC.

Northeast India Homegardens are recognized worldwide as sustainable agroforestry systems that are repositories of species and genetic diversity. Species diversity and composition of homegardens are influenced by a number of environmental, socioeconomic, and cultural factors. The present study examines the tree species diversity in the homegardens of different cultural groups of Barak Valley, Assam, Northeast India. Complete enumeration was done for diversity analysis in 181 homegardens from 38 villages in the three districts of the Valley. Factors affecting plant diversity were analyzed, and the floristic composition of the homegardens was found to vary with garden size, ethnicity of the homegarden owners, and geographical parameters such as location and altitude. Results indicate high plant diversity, with a total of 161 tree species identified from 47 families. Tea garden labor communities were comparatively found to hold more diversity in their homegardens. Similarity and cluster analysis revealed the distinctness of the majority of the homegardens, and seven groups of homegardens with very low distance were revealed. Homegardens were also found to maintain considerable conservation value as repositories of many underutilized, wild, and rare plant species. Biodiversity conservation in the homegardens was found to be linked to the multiple values of the different plant species to the homegardeners and further highlight the concept of the Bconservation through use^ap-proach. For the preservation of such traditional agroforestry systems, which also have the potential to provide options for adaptation to climate change, proper documentation of traditional knowledge concerning the different plant species and the human-nature interaction in the homegardens is necessary before such systems are completely lost.

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