Forest Structure, Diversity and Regeneration Pattern Along Altitudinal Gradient in Temperate Zone of Nanda Devi Biosphere Reserve (a World Heritage Site), Western Himalaya, India

present exhibited forest structure, plant species composition and regeneration pattern in temperate of Nanda Devi Biosphere Reserve (NDBR), western along the different The contain


Conclusion
Our results suggest to monitor the change in vegetation structure, species composition and regeneration pattern, we should establish permanent study plots in different forest types located along the elevational gradients for an effective and comprehensive monitoring programme to tracks the response of changing climate at both community and species level. Therefore, it is necessary to development of appropriate weather and meteorological station in this sensitive and ecologically important area for regional projection of micro climatic condition and generation of scienti c data on changing vegetation composition and advancement of the native species.

Background
The Himalayas regions most diverse ecosystem on the earth with a variety of plants species, high endemism and forest types due to the wide altitude gradient, topography, soil, climate and geographical location (Mani 1978 Himalayan region cover about 5 lakh km2 (about 16.2% of country's total geographical area) and forms the northern boundary of the country. Himalayan region recognized as one of the hotspots of biodiversity and harbors nearly 8,000 species of owering plants, of which 25.3% are endemic (Singh and Hajra 1996). Forest structure, species composition and regeneration patterns are most crucial ecological attributes of healthy forest ecosystems which exhibit variations in response to change in climate as well as anthropogenic complexities (Gairola et al. 2008; Krauchi et al. 2000; Dolezal and Srutek 2002). Elevation play major role to determine the structure of vegetation in most mountain of the world (Zhang et al. 2006; McVicar and Korner 2012). However, several studies have been carried out to assess the qualitative and quantitative characters of the vegetation in Western Himalaya (Saxena and Singh 1982;Rawal and Pangtey 1994;Baduni and Sharma 1996;Dhar et al. 1997;Rawat et al. 2001;Adhikari et al. 2004;Joshi et al. 2004), and other parts of the world (Shaw 1909; Goldsmith and Smith 1926;Griggs 1938; Allen and Walsh 1996;Holtmeier 2003;Schickhoff 2005), mostly revealed hump shaped (high species diversity at middle of gradient) distribution of species (Austrheim 2002;Zhang and Ru 2010). The population structure, characterized by the presence of su cient population of seedlings, saplings and adults, indicates successful regeneration of forest species (Marks 1974;Vablen et al. 1979; Pritts and Hancock 1983;Saxena et al. 1984; Khan et al. 1987), and the future composition of the forests depends on the potential regenerative status of tree species within a forest stand in space and time (Henle et al., 2004). The studies on forest composition, structure, plant diversity and regeneration of different part of NDBR have been studied but particularly in Ghangaria and Tolma sites of present study has so far not been analysed along altitudinal gradients. The Tolma site is way to approach the core zone of the reserve and old trekking route of the tourist before the noti cation as reserve. However, the Ghangaria site in uenced by the Sikh pilgrims (visited to Hemkund Sahib, sacred place of Sikh community), tourist visited Valley of Flower National Park (another core zone of the reserve) and inhabitants who has constructed permanent and temporary shops, lodges and small hotel and restaurants for income generation during summer season.
The hypothesis of the present study was that: (i) Forest structure, species composition and regeneration status change along the altitudinal gradient up to timberline ecotone (ii) Does altitude in uence the species diversity?. To test the hypothesis, the following objectives were envisages: (i) To assess the forest structure, species composition and regeneration status of forest stand along altitudinal gradient. (ii) To assess the physiochemical properties of soil with relation to the forest stand. Therefore, present study expected to provide scienti c information and baseline data that can be used for halt the biodiversity and help to develop the effective conservation and management plans for these ecological sensitive ecosystems.

Study site
The study was conducted at two different sites of Nanda Devi Biosphere Reserve (NDBR) timberline ecotone viz., (A) Ghangaria and (B) Tolma region (buffer zone), covering an area between 30°16' N to 30° 41' N and 79° 33' E to 79° 44' E with elevation ranges from 2800 m to 3400 m asl in the Central Himalaya. This biosphere reserve was recognized as a World Heritage Site in 1992 and was included in the UNESCO's world network of Biosphere Reserves in 2004. The reserve covers an area of about 5860 km 2 with two core zonesthe Nanda Devi National Park (624.62 sq. km) and the Valley of Flowers National Park (87.50 sq km). There are three seasons-summer (April-June), rainy season (June -September), and winter (October-March), and the average annual rainfall is 928.81 mm. About 47.8 % of the annual rainfall occurs over a short period of two months (July-August) due to the strong in uence of the monsoon. The maximum temperature ranges from 11 to 24 0 C and the minimum from 3 to 7.5 0 C (Fig. 1). The altitudinal range of the biosphere reserve varies from 2,100 m asl to 7,817 m asl.

Vegetation sampling
Vegetation analysis was carried out by using strati ed random design sampling at two sites of timberline area in NDBR. A total of 146 plots (73 in each site) of 10 m × 10 m were laid randomly between 2600 m asl to 3600 m asl for enumeration of tree species. Each plot (10×10 m) was further subdivided into 5 m × 5 m sub-plots for enumeration of shrub and saplings, and 1m × 1m for seedlings and herb species (Misra 1968). The vegetation data were quantitatively analyzed for abundance, density and frequency according to Curtis and McIntosh (1950) and Misra (1968). The relative values were summed up to represent important value index (IVI) given by Curtis (1959). The diversity index (H') was computed by using Shannon-Weaver information Index (Shannon and Weaver, 1949). The regeneration status of dominant tree species was assessed based on the proportional distribution of density of individuals in each seedling, sapling and adult tree). The regeneration status of tree was considered "good" when seedling density > sapling density > adult tree density, "fair" when seedling density > sapling density ≤ adult density, "poor" when the species survived in only the sapling stage but not in the seedling stage, "none", for species with no sapling or seedling stages but present as adult trees, and "new" when adults of a species were absent but sapling and/or seedling stage(s) were present (Shankar 2001;Paul 2008).

Physiochemical properties of soil
The soil analysis of different aspect of the study area was conducted to determine the physiochemical characteristics of soil at different altitude gradient. The moisture percentage, water holding capacity (%) and texture of soil was determined as the methods described by Misra (1968). Soil pH (1:2.5, soil: water) was used to measure with the help of dynamic digital pH meter. Soil organic carbon (%) was determined by Walkley and Black's rapid titration method (Walkley and Black 1934). Total N was determined using the micro-Kjeldahl approach, exchangeable phosphorus (P) and available potassium (K) was determined by (Jackson 1958).

Statistical analysis
The abundance data were statistically analyzed for mean, standard deviation, correlation, ANOVA and t-test using Microsoft O ce, 2007.

Result
Floral diversity A total of 223 species of vascular plants (angiosperm, gymnosperm and pteridophytes) were identi ed within the study area. These species belong to 57 families and 165 genera. Of these, 46 families and 151 genera belonging to angiosperm, 4 families and 5 genera of gymnosperms and 7 families and 9 genera of pteridophytes were found at both study sites between 3000-3600 m asl. Among the owering plants (angiosperms and gymnosperms), the percent proportion of the life forms recorded as 4.6% trees, 18.77% shrubs and remaining 76.63% were herbs and forbs. Rosacaeae (17.69%) family was exhibited dominant followed by Asteraceae (14.97%), Ranunculaceae (12.93%), Lamiaceae and Poaceae (7.48% each). (Table 1). Species richness and diversity The total species richness (tree and shrub) was found higher in Ghangaria as compared to the Tolma site.
Most of the tree and shrub species were common at both the sites thus, resulting 90% similarity in tree layer and 60% similarity in shrub layer. Diversity index values were obtained slightly higher at Ghangaria site (7.9) as compared to Tolma site (7.84). However, the concentration of dominance (CD) particularly for the tree, sapling & seedling layer was found higher at Tolma site as compared to Ghangaria site, whereas, shrub layer showed higher CD at Ghangaria site (Table 2).  Table 3). The higher seedling density was recorded for R.
campanulatum (320 sapling ha −1 ) followed by Betula utilis (232 sapling ha −1 ) at Ghangaria site, while at Tolma site, higher density was found for Betula utilis (544 sapling ha −1 ) and Salix sikkimensis (268 sapling ha −1 ). Abies pindrow was another associate species exhibited higher sapling density at both sites (168 sapling ha −1 and 244 sapling ha −1 each site). In the seedling stratum, the maximum total density was recorded at Tolma site (2328 seedling ha −1 ) as compared to the Ghangaria site (2032 seedling ha −1 ). Among the species, higher seedling density was recorded for Betula utilis at both the sites (920 seedling ha −1 and 456 seedling ha −1 each site) followed by Rhododendron campanulatum (428 seedling ha −1 ) and Abies pindrow (364 seedling ha −1 ). (Table 5).  Regeneration potential In all 12 tree species were found along an elevational gradient between 3000-3600 m asl at both buffer areas of NDBR. Among all these tree species, 56% showed fair regeneration, 22% showed good regeneration, 11% exhibited poor and remaining (11%) indicated no regeneration at Ghangaria site; while at Tolma site, 40% species showed fair regeneration, 40% had good regeneration and remaining 20% exhibited no regeneration. In Ghangaria site two species viz., Salix sikkimensis and Rhododendron campanulatum showed good regeneration as both the species represented by good number of seedlings and saplings.

Soil characteristics
Soil water holding capacity (49.94 ± 5.63) and moisture content (60.43 ± 9.71) was found higher in N-aspect as compared to S-aspect at Tolma site. However, Ghangaria site also exhibit higher WHC (33.50 ± 4.54) for Naspect while soil moisture showed maximum (63.77 ± 4.77) in S-aspect. Tolma site revealed maximum bulk density for S-aspect (0.91 ± 0.10) as compared to N-aspect while Ghangaria site ranged between 1.03 g cm 3 to 1.06 gcm 3 in S and N-aspect, respectively. As far as soil structure concerned sand was the prime constituent of the soil in both aspect and sites, however decreasing trend was observed in silt proportion with increasing altitudinal. The soil pH ranged between 6.54 to 6.77 and 6.28 to 6.94 in Tolma and Ghangaria site,

Discussion
The community structure and regeneration status of the plant species could be predicted from the relative proportion of seedlings, saplings and adults in the total populations of different species. The present study exhibit the regeneration of the dominant species was quite moderate except for the Betula utilis and Rhododendron campanulatum. The higher seedling and sapling density of Betula utilis along the timberline is predicted better growth, survival and the advancement, but negligible in the near settlement and highly The present study showed huge variation in the density, basal area and species diversity in temperate forest ecosystem due to the topography, altitudinal variation, forest type and micro climatic conditions (  Cyperaceae, Lamiaceae, and Utricaceae as the diverse families of India. Therefore, the result of study also explicit that across various temperate forests of the world having a close similarity is an evident at the families' level. Maximum shrub density was recorded for Ribies alpester and Berberis jaeschkeana while minimum observed for Sorbaria tomentosa and Rubus niveus in Ghangaria and Tolma site, respectively. The dominant herbaceous species followed the sequence i.e., Fragaria nubicola > Oxalis corniculata > Geranium wallichianum > Anaphalis triplinervis > Impatiens sulcata in Ghangaria site. However, Geranium himalayense was recorded dominant species with Oxalis corniculata and Fragaria nubicola as co-dominant species at Tolma site.   2 and 3). In the context of frequency, seedling, sapling and tree of S-aspect were highly correlated with seedling, sapling and trees of N-aspects at both sites of the reserve (signi cant at p ≤ 0.05) (Tables 8 and 9).  Table 9 Correlation matrix of oristic composition on the basis of frequency indicator at Tolma site, NDBR.   Table 7).
The study revealed that intense recruitment of seedling and sapling of Betula utilis and Rhododendron campanulatum along the altitudinal gradient up to the upper timberline may be due to the more favorable climatic conditions for growth during past decades, and/or to land use changes in the high-altitude regions projected the great potential for future vegetation advancement. This study also exhibited the continuous decrease in the diameter (CBH) of trees and augmentation of sapling and seedlings of Betula utilis and Rhododendron campanulatum along an altitudinal gradient is clear indication that these species may move upward to the higher altitude. With increased global warming, the vegetation of high altitude areas would be expected to advance upwards, but yet the changes observed in both study areas have been limited to enhance the recruitment and growth of species rather than vegetation advancement. However, to con rm the shifting of vegetation in NDBR, the long-term studies are required through establishment of permanent plots with manual as well as automatic weather data recording set ups. The upper limit of survival of the plant species is still unknown from these areas since no long term scienti c data available on one hand and at the same time as the region has been under high anthropogenic pressure during recent past.

Conclusion
Our results suggest to monitor the change in vegetation structure, species composition and regeneration pattern, we should establish permanent study plots in different forest types located along the elevational gradients for an effective and comprehensive monitoring programme to tracks the response of changing climate at both community and species level. In addition, many important tree species of the reserve have already been listed in the rare and endangered categories, i.e., Taxus baccata, Juniperus spp. and Betula utilis. These species are over exploited, legally or illegally, to a great extent and increased rates of destruction and the in uence of a changing climate have made the situation worse. Therefore, it is necessary to development of appropriate weather and meteorological station in this sensitive and ecologically important area for regional projection of micro climatic condition and generation of scienti c data on changing vegetation composition and advancement of the native species. Figure 1 The annual rainfall occurs over a short period of two months (July-August) due to the strong in uence of the monsoon. The maximum temperature ranges from 11 to 24 0C and the minimum from 3 to 7.50C