The Himalayan alpine treeline varies depending on altitude and aspects, supporting a variety of plant species. In recent years, climate changes have exerted pressure on the vegetation in this region, challenging its adaptation to rapidly changing environmental conditions. This systematic review commenced by formulating a research question on the impact of climate change on Himalayan alpine treeline vegetation and conducted a thorough literature search, adhering to the PRISMA protocol. The rising temperatures, altered precipitation patterns, and other climate-related factors have initiated an upward shift in the treeline that threatens the unique biodiversity of the region. Indeed, in various parts of the Himalayas, there is evidence of the treeline moving upwards, altering plant regeneration and growing season, and impacting soil properties. There is a shift of vegetation ranging from 0.80 to 503.00 m in Himalayan treeline regions have been reported in various studies. Abies spectabilis and Betula utilis are the most sensitive, showing the highest upward shifts due to climate change. The repercussions of climate change on the Himalayan alpine treeline are anticipated to have significant ecological implications. Most species at the Himalayan alpine treeline exhibit poor regeneration status, while some others reveals good, fair, or no regeneration. Consequently, new regeneration patterns are emerging. Changes in soil temperature and physicochemical properties due to climate warming are ultimately affecting Himalayan alpine treeline vegetation. Additionally, shifts in the growing season and phenophases of various tree species have also been observed. The profound and far-reaching impacts of climate change on the Himalayan alpine treeline necessitates implementing mitigation and adaptation strategies to safeguard the delicate alpine ecosystems of the region.

Forests face a variety of threats in the modern era. Agroforestry systems, both traditional and introduced, have a tremendous capacity for providing sustainable resources and combating the impact of global climate change. Indigenous agroforestry and forest land-use systems are important reservoirs for biodiversity conservation and ecosystem services, providing a potential contribution to livelihood security for rural communities. This study aimed to assess the tree diversity and carbon stock of agroforestry and adjoining forests along altitudinal gradients, ranging between 700 and 2200 masl (i.e., lower, middle, and upper altitudes) by laying sample plots randomly of a size of 20 × 20 m². In the forest land-use system, the maximum Importance Value Index (IVI) included Dalbergia sissoo (71.10), Pyrus pashia (76.78), and Pinus roxburghii (79.69) at the upper, middle, and lower elevations, respectively, whereas, in the agroforestry land-use system, the IVI reported for Ficus semicordata was 43.05 at the upper, while for Grewia optiva it was at 53.82 at the middle and 59.33 at the lower altitudes. The below-ground biomass density (AGBD) was recorded as 1023.48 t ha⁻¹ (lower), 242.92 t ha⁻¹ (middle), and 1099.35 t ha⁻¹(upper), while in the agroforestry land-use system, the AGBD was 353.48 t ha⁻¹ (lower), 404.32 t ha⁻¹ (middle), and 373.23 t ha⁻¹ (upper). The total carbon density (TCD) values recorded were 630.57, 167.32, and 784.00 t ha⁻¹ in forest land-use systems, and 227.46, 343.23, and 252.47 in agroforestry land-use systems for lower, middle, and upper altitudes, respectively. The Margalef’s Index values for agroforestry and forests ranged from 2.39 to 2.85 and 1.12 to 1.30, respectively. Soil organic carbon (SOC) stock recorded 45.32, 58.92, and 51.13 Mg C ha⁻¹ for agroforestry and 61.73, 42.65, and 71.08 Mg C ha⁻¹ for forest in lower, middle and upper elevations, respectively. The study suggests that selecting land use patterns can be an effective management system for tree species at different elevations for carbon storage, helping to mitigate climate change and aiding in sustainable management of ecosystems in the Garhwal Himalayas.

Background: The ability to produce seeds when pollinators or potential mates are scarce is one of the principal advantages of self-pollination in flowering plants. However, the role of pollinators mediating self-pollination to ensure seed set when pollen or potential mates are limited has received less attention. This study examined the reproductive consequences and involvement of pollinators in assuring seed set in an isolated tree ofMagnolia grandiflora, a predominantly outcrossing species.Methods: We tested various aspects of reproduction such as flower density, floral rewards, stigma receptivity, pollinator abundance and behaviour, fruit set and seed set, in two successive reproductive years (2015–2016).Results: Flowers ofM.grandiflorapossess a suite of traits facilitating pollinator-mediated self-pollination (PMS), although the chances of autonomous self-pollination are reduced due to herkogamy, spatial separation of anther and stigma. The mean pollen production/flower was 5,152,289 ± 285,094 with a pollen-to-ovule ratio of 39430 ± 164. We found a significant positive correlation between number of visits and seed production for bees (r= 0.5099,p= 0.0007) and beetles (r= 0.7159,p= 0.00001), indicating these are effective at PMS. There was a significant negative correlation for thrips (r= – 0.3206,p= 0.044) and no correlation for flies or spiders. The percent fruit set was 100% and the seed set per ovule ranged between 19 and 20%.Conclusions: PMS will guarantee reproductive assurance and mitigate the effect of reduced mates or pollen limitation which is expected to increase the fecundity and establishment of individual trees in geographically isolated locations.

The management of forests is essential for the conservation of biodiversity and climate change. Studies on the variation in forest tree diversity and carbon sequestration by the forests along altitudinal gradients are limited for most parts of the Garhwal Himalaya. The present study was carried out in montane forests in a part of district Tehri of the Garhwal Himalaya, India at four different sites between altitudinal ranges of 850 to 2,200 masl (i.e., 850–1,500 masl under sub-tropical region and 1,800–2,200 masl under temperate region) for vegetation, soil, and carbon stock analysis using different parameters including the existing pressure on the sites for fuel, fodder, timber, grazing, and browsing. All the standard methods were used for vegetation and soil analysis. The highest value of tree diversity (H = 0.48) and concentration of dominance (CD = 0.95) was recorded at 850–1,100 masl altitude under sub-tropical forests. The aboveground biomass density (AGBD) and belowground biomass density (BGBD) ranged from 271 to 703.20 and 83.21 to 163.92 Mg ha^–1, respectively. The pH value ranged from 5.63 to 6.86 (0–15 cm) and 6.17 to 7.21 (15–30 cm). Similarly, soil organic carbon (SOC) was reported to range from 1.86 to 2.57% and 1.78 to 2.44% at 0–15 cm and 15–30 cm depths, respectively. Available nitrogen (N) under temperate forests was reported to be significantly higher than at other altitudes. Among the studied parameters, a significant positive correlation was reported between the pH of the soil and the Shannon–Wiener and Margalef diversity indices. The study revealed that the sub-tropical region was more diversified in terms of tree species whereas soil properties were reported to be better in the temperate region. Among the species in the study region, Pinus roxburghii, Boswellia serrata, Quercus leucotrichophora, and Cedrus deodara have shown good potential for carbon storage. Thus, based on the dominant and associated species present in the area, forest management activities may be followed for the survival and regeneration of species with the potential of being the next dominant species in the future.

The year-to-year variations in flowering, pollen and fruit production in ten Gmelina arborea individuals in a natural forest were observed over a period of five years, 2009−2013, and pollinator visits were observed closely over two years, 2011 and 2012. A pollen supplementation experiment was also undertaken in two years (2011 and 2012) of contrasting flowering levels. Considerable year-to-year variations were observed in flower, pollen and fruit production. The observed variation represented a normal sequence of good-year and poor-year cycling which is most parsimoniously attributed to resource allocation. The average level of pollen production per individual tree in good flowering years oscillated between 6.6 and 9.62 × 10⁸, which in the poor flowering years was between 1.92 and 3.07 × 10⁸. The magnitude of pollen limitation across years was highly significant (p < 0.0001). Fruit set through supplemental pollination was 73% and 96% greater than that of the open-pollinated branches in the year 2011 and 2012, respectively. Pollen limitation, irrespective of the arrival of outcross pollen, can reduce annual seed set in predominantly bee-pollinated trees. However, various other factors may cause flower abortion in addition to pollen limitation. The results of this study would be very valuable to the seed orchard managers and the silviculturists to manage the seed production areas (SPAs) of G. arborea. The study ultimately recommends supplemental pollination in seed orchards of G. arborea for better genetic gain and good seed yield.