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.

Bhimal (Grewia oppositifolia) is the most important agroforestry tree species used for fodder, fuel and fiber in the Himalayan region. In the present study, G. oppositifolia-based traditional agroforestry systems were selected for the estimation of carbon stock and the production potential of barnyard millet (Echinochloa frumentacea) and finger millet (Eleusine coracana), with two elevational ranges, i.e., 1000–1400 and 1400–1800 m amsl, in Garhwal Himalaya, India. The results of the investigation showed a decline in the growth and yield attributes of both the millet crops under the G. oppositifolia-based agroforestry system at both elevations as compared to their respective control sites (sole crops). Among the elevations, the total number of tillers per plant (2.70 and 2.48), the number of active tillers per plant (2.18 and 2.25), panicle length (17.63 cm and 6.95 cm), 1000-seed weight (5.49 g and 4.33 g), grain yield (10.77 q ha⁻¹ and 11.35 q ha⁻¹), straw yield (37.43 q ha⁻¹ and 30.15 q ha⁻¹), biological yield (48.21 q ha⁻¹ and 41.51 q ha⁻¹) and the harvest index (22.53% and 27.78%) were recorded as higher in the lower elevation in both E. frumentacea and E. coracana, respectively, while plant population per m² (18.64 and 25.26, respectively) was recorded as higher in the upper elevation. Plant height for E. frumentacea (180.40 cm) was also observed to be higher in the upper elevation, while for E. coracana (98.04 cm), it was recorded as higher in the lower elevation. Tree carbon stock was reported negatively with an increase in altitude. The maximum amount of sequestered carbon in the tree biomass for G. oppositifolia was 23.29 Mg ha⁻¹ at the lower elevation and 18.09 Mg ha⁻¹ at the upper elevation. Total carbon stock in the tree biomass was reported to be the highest (15.15 Mg ha⁻¹) in the 10–20 cm diameter class, followed by 20–30 cm (6.99 Mg ha⁻¹), >30 cm (2.75 Mg ha⁻¹) and the lowest (2.32 Mg ha⁻¹) in the <10 cm diameter class. The results show that the yield of E. frumentacea and E. coracana was not reduced so severely under the G. oppositifolia system; however, keeping in mind the other benefits of this multipurpose tree, i.e., carbon sequestration and socioecological relevance, farmers can get benefit from adopting these crops under G. oppositifolia-based agroforestry systems.