Elevational behaviour on dominance–diversity, regeneration, biomass and carbon storage in ridge forests of Garhwal Himalaya, India

Abstract

The present study was conducted along the elevational gradient in ridge forests of Bhagirathi catchment area of Garhwal Himalaya. The purpose of the study was to understand the growth behaviour of tree species at different altitudes in terms of dominance–diversity, regeneration dynamics, biomass and carbon storage in forests of Bhagirathi catchment area. Plot design, with main plot size of 0.1 ha, was used to analyse quantitatively and qualitatively the tree, sapling and seedling vegetation. The maximum mean tree density (708 ± 153 trees ha–1) was recorded in Abies spectabilis–Quercus semecarpifolia forest association (between 2800 and 3100 m asl), while minimum (425 ± 32 trees ha–1) in Q. semecarpifolia–Cedrus deodara forest association (between 3100 and 3400 m asl). The total basal cover values ranged between 28.80 ± 5.27 m2 ha–1 (below 700 m asl) to 99.69 ± 29.64 m2 ha–1 (above 3400 m asl). The highest Shannon index value (0.83 ± 0.14) was observed in Anogeissus latifolia–Mallotus philippensis forest association whereas, lowest (0.26 ± 0.09) in Q. semecarpifolia–C. deodara forest association. The maximum similarity (85.23 ± 5.04%) was noticed in Quercus floribunda–Rhododendron arboreum forest association while, minimum (59.32 ± 5.18%) in A. latifolia–M. philippensis association. Similarly the species richness, Simpson index, Shannon index, seedling density, total basal cover and above ground biomass density showed positive–significant elevation–wise variation in various growth phases (i.e., tree, sapling and seedling). The total biomass density values oscillated from 189.38 ± 14.35 Mg ha–1 (between 1600 and 1900 m asl) to 520.72 ± 114.57 Mg ha–1 (between 3100 and 3400 m asl). Consequently, the total carbon density at various elevational ranges varied from 85.22 ± 6.46 Mg C ha–1 to 234.32 ± 51.56 Mg C ha–1 for the corresponding elevations. The Detrended Correspondence Analysis (DCA) clearly indicated the prevalence of distinct habitats and resultant associations of tree species in various ridge forests whereas, on the other hand the Canonical Correspondence Analysis (CCA) has shown a complex interrelationship amongst species clustering, mountain ranges and climatic/environmental variables. The study revealed that the Pinus roxburghii was invariably affecting the habitats of mixed broad–leaved forests at lower altitudes, whereas Cedrus deodara was noticed to encroach continuously the higher elevational habitats. The study has also indicated that the old growth coniferous and broad leaved forests of higher altitudes of Garhwal Himalaya (like A. pindrow, A. spectabilis, A. acuminatum, B. utilis, C. deodara, Q. semecarpifolia and R. arboreum) have more carbon storage potential and hence recommended for carbon management through afforestation at higher altitudes of Himalaya.