INTRODUCTION
Forest ecosystems play an important role in global biogeochemical cycles
and mitigate the negative impact of climate change (Hui et al., 2017).
Furthermore, forests act as a key carbon pool (C) and store more carbon
per unit area than any terrestrial ecosystem (Dixon et al., 1994; Pugh
et al., 2019). Figures suggest that half of the carbon in the
terrestrial ecosystem is stored in forests (Pan et al., 2011; Popkin,
2019). Forest stand growth can change the forest structure, biomass, and
soil nutrient content (Shanin et al., 2014; Goebes et al., 2019). The
distribution of carbon stocks in different elements of ecosystems is one
of the important features of succession (Robinson et al., 2015;
Badalamenti et al., 2019). Natural vegetation in freshly degraded
land/slip and the naturally regenerated forest is an effective way to
deter soil degradation, tree establishment, improve the ecological
environment, and drives succession (Walker, & del Moral2009;
Berrahmouni et al., 2015; Pandit et al., 2018). Early succession species
have strongly favored by vegetation restoration efforts due to their
capability of tolerating extremely harsh environmental conditions
(Walker, & del Moral2009). After forest degradation, early successional
species invade the habitat and radically alter vegetation and soil
physicochemical properties (Lebrija-Trejos et al., 2010).
Early-successional forest ecosystems that grow after forest degradation
or stand- replacement are very important, particularly in terms of
carbon storage by pioneer trees after landscape recovery (Swanson et
al., 2010; Preem et al., 2012; Lorenc-PluciĆska et al., 2013; Becker et
al., 2015). The ability of Alnus tree to fixing nitrogen from the
air through symbiotic with nitrogen-fixing bacteria, collectively calledFrankia , generates to the concept that this tree could be
effective agents to tolerating extremely harsh environmental conditions
and accelerate the natural succession. Alnus is found mostly in
degraded habitats with nutrient impoverished conditions in the soil
(Sharma et al., 1998; Resh et al., 2002;
Binkley.,
2003; Perakis and Pett-Ridge 2019). Additionally, alder also produces
cluster roots which secrete carboxylates and mobilizes available
phosphorus and other mineral elements in the soil (Lambers et al.,
2019).
Nitrogen-fixing Nepalese alder (Alnus nepalensis D. Don.) being
an early successional species arises as a pioneer in post-disruption
(landslides/ landslips) in most Himalayan forests below 2500 m (Sharma
et al., 1998; Rana et al., 2018; Joshi and Garkoti 2020). In the central
Himalaya, A. nepalensis often forms pure patches and sometimes
grows in association with white oak (Quercus leucotrichophora A.
Camus) as well as other broad-leaved species throughout different stages
of forest succession after disturbance (Singh, 2014; Frouz et al., 2015;
Joshi and Garkoti 2020). Owing to the association of Frankia in
roots, the Alnus species fix nitrogen and have a stronger impact
on soil physicochemical
characteristics
(Binkleyet
al 1992; Myrold et al., 1994; Resh et al., 2002;
Binkley.,
2003; Khan et al., 2007; Bissonnette et al., 2014; Perakis and
Pett-Ridge 2019; Krishna et al. 2019). Therefore, it is widely used in
agroforestry, forest management, and restoration systems and also has
long been traditionally used as an intercropping tree species (Semwal et
al., 2013; Sakalli et al., 2013; Sakalli et al., 2017; Rana et al.,
2018). Despite a large series of studies addressing the advantages ofAlnus species, knowledge on biomass C storage variations in alder
species or alder mixed forest ecosystems in the central Himalayas is
still limited. The proposed work envisages the role of A.
neplanesis in the recovery of degraded ecosystems in central Himalaya.
In the present study, a comprehensive analysis of the carbon storage in
soil and vegetation along a chronosequence in A. nepalansisforest stands in central Himalaya is presented. The study was conducted
to determine: (1) assess the above-and below-ground carbon storage of
different A. nepalansis forest stands in central Himalaya (2)
estimate carbon stock dynamics in the whole ecosystem (plant, litter,
and soil) in of different A. nepalansis forest stands and (3)
evaluate the role of A. nepalensis in influencing total ecosystem
C pools as well as provide helpful suggestions on how to manage forests
to mitigate impacts of climate change.