2.1. Study area: The study was carried out during 2019-20 in the Sindh range of forest division Ganderbal. The experimental site covers an area of 21807 hectares with 39 compartments. Geographically the site lies between 74º 42ʹ to 75º 26ʹ East longitude to 34º 28ʹ North latitude with an altitude ranging from 1600m to 5200m above sea level within the central Circle of Kashmir Province. The study employed a stratified random sampling method, using quadrates measuring 10m x 10m for trees. These quadrants were further subdivided into 5m x 5m and 1m x 1m quadrants for shrubs and herbs, respectively. Mature, even-aged stands were chosen for assessing biomass and carbon sequestration potential, including Cedrus deodara, Robinia pseudoacacia, Cupressus torulosa, Prunus arminiaca, Ailanthus altissima, and a mixed stand comprising Cupressus torulosa, Robinia pseudoacacia, and Ailanthus altissima, along with a grassland area denoted as T1, T2, T3, T4, T5, T6, and T7, each with three quadrants per treatment, arranged in a randomized block design.
2.2. Aboveground tree biomass: For assessing the aboveground tree biomass within each stand, 10m x 10m quadrants were established. The volume of all trees within each quadrant was calculated using a specific formula.
Volume = Form factor × basal area × Height
F = \(\frac{2\varvec{h}}{3\varvec{H}}\)
Basal area = \(\frac{{\varvec{\pi }\varvec{d}}^{2}}{4}\)
d = diameter at breast height
h = height at which diameter is half of dbh
H = total height
F = form factor (Bitterlich, 1984)
The diameter at breast height was measured using a caliper, while tree height was measured using Ravi’s multimeter. To estimate aboveground tree biomass, the volume was multiplied by a specific gravity value obtained from literature (Kaul and Sharma, 1983).Biomass = Volume × specific gravity
2.3. Below ground tree biomass: Below ground biomass for all species was determined by multiplying aboveground biomass with 0.25 (FAO, 1997).
2.4. Shrub biomass: For assessing shrub biomass, the 10m x 10m quadrants designated for trees were subdivided into 5m x 5m quadrants to specifically target shrubs. Representative samples from each category were chosen to ascertain the number of stems, branches, and leaves. These samples were carefully stored in paper bags and then subjected to drying in an oven at 70°C for 72 hours to determine their dry biomass. The total aboveground biomass was calculated by multiplying the number of stems in each category by their respective dry biomass. Belowground biomass of the shrub was determined by extracting the entire root system from the soil, washing the roots, and then drying them in an oven at 72°C for 42 hours to measure their dry weight.
2.5. Herb biomass: To evaluate herb biomass, the 5m×5m quadrants designated for shrubs were subdivided into 1m×1m quadrants specifically for herb assessment. Herb samples were collected and transported to the laboratory for a phytosociological study, where they were sorted by species and thoroughly washed with fresh running water. Subsequently, the samples were segregated into different paper bags. Afterward, the samples underwent drying in an oven at 80°C for 48 hours until reaching a constant weight. Each sample was then individually weighed to estimate its biomass, following the methodology outlined by Gupta and Dutt (2005).
2.6. Carbon stock under different silvopastoral systems: The calculation of aboveground carbon stock in trees involved multiplying the aboveground biomass by a carbon conversion factor of 0.5, as outlined by Koach (1989). Similarly, the belowground tree carbon stock was determined by multiplying the belowground biomass by a carbon conversion factor of 0.45, following the methodology established by Woomer (1999). Additionally, the carbon stock of understorey vegetation was assessed by multiplying the biomass by a carbon conversion factor of 0.45, also based on the research by Woomer (1999).