2.2. Experimental design and sampling
In October 2018, six forest stands (1) A. nepalensis- early
regeneration (AER) forest, (2) A. nepalensis -late regeneration
(ALR) forest, (3) A. nepalensis -planted by the forest department
in the degraded forest (APDF) (4) A. nepalensis - mature oak mixed
(AMOM) forest, (5) A. nepalensis - mix with rhododendron (AMR)
forest, and (6) A. nepalensis –mix with old oak (AMOO) forest in
a chronosequence of A. nepalensis forest stands were randomly
selected from the entire area of the Kedarnath valley. Proportion to the
total basal area of A. nepalensis of the stand was the primary
criteria for stands selection. In each sampling stand, three 0.1 ha
plots were established using a stratified random sampling design. Each
plot was subdivided into ten (10 m x 10 m sized) quadrats for biomass
and carbon inventory. Species density and tree diameter at breast height
(DBH) were recorded in each plot. Tree biomass, including the biomass of
bole, branch, twig, foliage, catkin, stump root, lateral root, and fine
roots was estimated in plots by already developed allometric equations
(Rawat, & Singh, 1988; Adhikari, 1994; Sharma &Ambhasht 1990; Sharma,
2011). Three 5 m x 5 m quadrats were layed to study Shrubs and three 1 m
x 1 m sized quadrats were used for herbs and litter Shrubs were
harvested and separated into branches, roots, and leaves; herbs were
harvested and separated into above-and belowground components from each
subplot. Components of shrubs, herbs, and litter were brought to the
laboratory and oven-dried at 64 °C for 48 h and weighed to estimate the
ratio of fresh weight to dry biomass (Mg ha-1). The
total vegetation C stock was computed by assuming that carbon content is
47.4% of the total biomass (Martin and Thomas, 2011). Soil samples were
randomly collected with soil corers (diameter, 5 cm) at up to maximum
soil depths (0-10 cm in AER, 0-30 cm in APDF, 0-100 cm in ALR, AMOM, AMR
and AMOO plots) and divided in 0-10, 10-20, 20-30, 30-50, 50-80 and
80-100 cm. The soil samples were placed in plastic bags and brought to
the laboratory. The soil sample was air-dried, and visible plant debris
and stones were removed and ground to pass through a 2-mm sieve to
perform organic carbon analysis. Soil organic carbon (SOC) was
calculated using
K2Cr2O7-H2SO4oxidation (Nelson & Sommers, 1996). Bulk density was estimated for each
soil depth by weighting the whole sample and oven-dried at 105 °C for 48
h.
Soil carbon stock (SOCS) was calculated according to the following
equations:
\begin{equation}
\text{SOC\ stock\ }\left(\text{Mg\ ha}^{1}\right)=SOC\ x\ BD\ x\ D\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ (1)\ \nonumber \\
\end{equation}Where SOC (%) is soil organic carbon, D is the sampling depth (cm), BD
is the bulk density (g cm-3) and SCFs is the mass of
proportion of coarse fragments content (% of volume) using an average
rock density of 2.65 g cm-3.
Topographic feature (slope aspect, elevation, slope position, slope
angle) of each plot was measured and slope correction was applied for
final biomass estimation. Stands located on slope >10%,
slope correction was applied using the following equation:
\begin{equation}
L=Ls\ x\ Cos\ S\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ (2)\nonumber \\
\end{equation}Where L is the true horizontal distance of forest stands Ls is the
standard distance measured in the field along the slope and S is the
slope in degrees. The area of the sampled stands was then calculated as:
Area= stands width × calculated true stands length (L).