Background: The State of Arunachal Pradesh is part of the Himalaya biodiversity hotspots distributed over an area with the largest elevation gradients in the world, ranging from lowland tropical forests to alpine vegetation. Methods: The vegetation was surveyed along an elevation gradient ranging from 87 to 4161 m in 354 belt transects (500 m × 10 m in size) and analyzed using various ecological indices. Results: A total of 482 (458 identified, 24 unidentified) plants were recorded in the present study, of which 153 are nonwoody herbs and grasses (145 identified) belonging to 55 families, and 329 are woody trees and shrubs (313 identified) belonging to 74 families. The 458 identified species belong to 117 families and 251 genera, of which 94.10% are phenerogams (Angiosperms: 421 species [spp.] and Gymnosperms: 10 spp.) and 5.90% cryptogams (Pteridophytes: 27 spp.). The family Fabaceae contributed the greatest species diversity with a total of 27 plant species (Papilionaceae: 10 spp., Mimosaceae: 9 spp. and Caesalpinaceae: 8 spp.) followed by Poaceae (21 spp.), Ericaceae (20 spp.), Asteraceae (18 spp.), Lauraceae (17 spp.), Euphorbiaceae (16 spp.), Urticaceae (15 spp.) and 49 monotypic families. The most dominant trees were Castanopsis indica (24 individuals per ha), followed by Quercus semicarpifolia (12 individuals per ha) and Pinus roxburghii (12 individuals per ha) and some bamboos (Dendrocalamus strictus: 69 individuals per ha; Bambusa pallida: 16 individuals per ha). The studied forest stands were rich in various bamboos; a total of 14 different bamboos were recorded in the present study including Dendrocalamus strictus, Bambusa tulda, B. pallida etc. Common IUCN red-listed species were Aquilaria malaccensis, Begonia tessaricarpa, Gledetsia assamica, Gymnocladus assamicus, Livistona jenkinsiana, Rhododendron meddenii, Rhododendron thomsonii collected from the Dirrang, Tawang, Yamcha, Itanagar, Along and Mebo areas of Arunachal Pradesh. Conclusion:The results confirm that the Eastern Himalayan forests are very rich in terms of species diversity which decreases with increasing elevation. Species richness and distribution patterns of plants are largely regulated by altitude and other environmental factors. Intensive monitoring and management is needed to protect this fragile ecosystem from the ever-increasing anthropogenic pressure and changing climatic conditions.

Abstract. Large-scale environmental gradients have been invaluable for unraveling the processes shaping the evolution and maintenance of biodiversity. Environmental gradients provide a natural setting to test theories about species diversity and distributions within a landscape with changing biotic and abiotic interactions. Elevational gradients are particularly useful because they often encompass a large climatic range within a small geographical extent. Here, we analyzed tree communities in plots located throughout Arunachal Pradesh, a province in northeast India located on the southern face of the Eastern Himalayas, representing one of the largest elevational gradients in the world. Using indices of species and phylogenetic diversity, we described shifts in community structure across the landscape and explored the putative biotic and abiotic forces influencing species assembly. As expected, species richness and phylogenetic diversity decreased with increasing elevation; however, contrary to predictions of environmental filtering, species relatedness did not show any clear trend. Nonetheless, patterns of beta diversity (both taxonomic and phylogenetic) strongly suggest lineage filtering along the elevational gradient. Our results may be explained if filtering is driving the assembly of species from distinct evolutionary lineages. New metrics exploring community contributions to regional taxonomic and phylogenetic beta diversity provided additional evidence for the persistence of unique communities at high elevations. We suggest that these patterns may be consistent with filtering on glacial relicts, part of once more diverse clades with convergent traits suited to climates at the last glacial maximum, resulting in random or over-dispersed community assemblages at high elevations. We propose that these high-elevation sites with evolutionarily distinct species represent possible regions for conservation priority that may provide refugia for species threatened by current warming trends.

No abstract

No abstract

Seedling survival and growth of two Rhododendron species viz., Rhododendron kenderickii and Rhododendron grandewere studied along an altitudinal gradient in a temperate forest. Differences in survivality and relative growth responses of the two selected rhododendrons in terms of height, collar diameter and leaf number were monitored seasonally. High seedling mortality was recorded highest in winter season as well as in the higher altitude. Both the species attain maximum growth in terms of height, collar diameter and mean leaf number during rainy season while, minimum in winter season. Moreover, both the Rhododendron species exhibit variation in growth response with altitude and higher total growth was recorded in lower altitude. The result of the present study showed that the survival and growth of seedlings of both the selected Rhododendron species were greatly influenced by altitude as well as season. This variability may be due to the variation in light, temperature, moisture and edaphic factors in various seasons as well as at different altitudes, which results into development of an array of microclimatic conditions for differential growth behavior of different species.