4.4. Implications for management
Our results revealed that the ecosystem C pools in the above and below-ground parts of the tree, shrubs, herbs, litter, and soil were changed significantly during A.nepalensis forests stand development. Developing forests has had a significant impact on biotic and abiotic factors, such as plant species, soil physicochemical properties, microbial communities, and the quantity and quality of inputs and outputs of organic matter (Myrold et al., 1994; Susaetaet al., 2014; Uri et al., 2014; Uri et al., 2017; Taeroe et al., 2017). The distribution of C between the plants and the soil during the development of the forest stand depends on the species of trees and A. nepalensis is a nitrogen-fixing tree that can change soil carbon more than any other non-nitrogen fixing tree. (Binkley et al., 1992; Myrold et al., 1994). A. nepalensis has been shown to support carbon storage in temperate forests in central Himalaya. The ecosystem C storage came primarily from A. nepalensis , which were more abundant and had a higher basal area than Q. leucotrichophora and R. arboreum. Our results provide new qualitative insight into the role of A. nepalensis in the temperate forest C sink in the central Himalaya. The Himalayan range is among the most fragile and unstable mountain regions of the world. Forest degradation in the Himalayas is a major challenge for forest managers and policymakers.The interplanting of nitrogen-fixing A. nepalensis with non-nitrogen-fixing tree species (Q. leucotrichophora and R. arboreum ) may enhance the growth of the non-nitrogen-fixing tree species by increasing nitrogen availability (Binkley et al., 1992; Myrold et al., 1994; Semwal et al., 2013) improving nutrient cycling and soil fertility (Binkley., 2003; Khan et al., 2007; Bissonnette et al., 2014) and increasing carbon sequestration rate and improving risk management. The observation thatAlnus raising soil nitrogen levels and subsequently influence the growth of the neighbor’s non-nitrogen-fixing species (Anthony and Klaus 2004). Maintaining or including nitrogen-fixing species in mixed forests appears to be an option for enhancing soil carbon sequestration rate (Resh et al., 2002). Previous study indicates that Alnus species contribute significantly to the supply of nitrogen in the forest ecosystem thus markedly benefits soil fertility. In addition to being an early successional species, A. nepalensis colonize the recently-disturbed area with low levels of nitrogen availability. The obtained results show that A. nepalensis may play the role of early successional species in the temperate forest in central Himalaya. High nitrogen-rich litter of A. nepalensis reduced requirement of nitrogen in the soil and thus increase the forest productivity, regulating C cycle and mitigate global climate change. In the central Himalaya, A. nepalensis is currently of little impotence in plantation forestry, although the potential for future use of A. nepalensis in forestry seems great and the opportunities are diverse.  Although A. nepalensis does offer an alternative to chemical application of nitrogen to the forest, this potential of A. nepalensis systems in forest management is much more. That knowledge can contribute to the sustainability of forest practices which can ensure the restore the degraded forest and maintain their capacity to provide other goods and services for the benefit of current and future generations.
CONCLUSION
Our results revealed that the abundance of A.nepalenis affect the ecosystem carbon storage. We found that tree biomass in different stands AER, APDF, ALR, AMOM, AMR, and AMOO were 8.97, 51.41, 16.07, 53.74, 144.77, and 101.14 Mg ha-1 respectively. Soil organic C (SOC) storage of soil in different soil depth in successional stages AER (0-10 cm), APDF (0-30 cm), ALR (0-100 cm), AMOM (0-100 cm), AMR (0-100 cm), and AMOO (0-100 cm) was 3.31, 31.21, 75.47, 157.04, 159.43 and 210.13 Mg ha-1, respectively, with SOC concentration decreasing with increasing soil depth.  The ecosystem carbon storage in the stand developing stand averaged 15.85, 183,216.26, 390.32, 403.66, and 500.08 Mg ha-1 in the AER, APDF, ALR, AMOM, AMR, and AMOO respectively. In addition, trees and soils were the two largest contributors to the total ecosystem carbon pool in all stands. The soil carbon content and storage were highly heterogeneous among different stands and soil depths. Species community structure and composition had a significant influence on the biomass carbon storage and soil organic carbon storage of the stands. Our results are useful in estimating the total ecosystem C stock value of A. nepalensisforests in the study area. The A. nepalensis play an important role in stand development and enhancing ecosystem carbon storage by ecological succession.  The expansion of A. nepalensis in central Himalaya can play an important role in regional carbon budge and degraded forest protection. Long-term monitoring and research are required to further explore the role of A. nepalensis forest stands in central Himalaya.