16 Banko Janakari, Vol 35 No. 2 A Comparative Study of Biomass and Carbon Stock in Tropical and Temperate Forests of Ilam District in Nepal Animesh Poudel , Krishna Prasad Dahal , Mohit Joshi , Sakshi Thapa Magar , Ripesh Kharel * Institute of Forestry, Tribhuvan University, Hetauda Campus, Hetauda. *Email: kharelripesh@gmail.com Quantification of biomass and carbon is imperative in optimizing ecological and low-carbon emission-oriented economic benefits of forestland. This study quantified stock densities of carbon in two distinct forests, viz., tropical and temperate. We selected two Community Forests (CFs) with predominance of Shorea robusta in the tropical and Castanopsis sp. in the temperate region of Ilam district (Chure and Mid-hill). Data were gathered using stratified systematic sampling with a 1% sampling intensity. It was discovered that the overall stock (carbon) in the Tropical and Temperate CFs was 95 Mg ha-1 and 75.59 Mg ha-1, respectively. Tropical forests exhibited a higher level of biomass (202.14 Mg ha-¹) relative to temperate forests (169.34 Mg ha-¹). The biomass carbon in tropical forests was 1.19 times greater (per hectare) compared to temperate forests. Interestingly, analysis revealed an absence of significant differences in carbon sequestration between the two forests under study with respect to diameter and height class. The study shows that both tropical and temperate forest stands sequester a significant amount of carbon, and appropriate management can yield additional benefits. Keywords: Carbon sequestration, Castanopsis, Community Forest, Shorea robusta Maintaining and increasing carbon stocks in forests worldwide is a crucial part of the global effort to combat climate change (UN, 2017; Raihan, 2024). The total amount of carbon within a pool at a specific time is different from sequestration, which is the process that accumulates carbon in pools outside of the atmosphere (FAO, 2011). Forest ecosystems are both sources and sinks of atmospheric carbon dioxide (Huang et al., 2020). They are among the most important options for carbon sequestration and play a crucial role in regulating the global carbon cycle (Salunkhe et al., 2018; Nugroho et al., 2022). As a natural process, the captured carbon is primarily absorbed as biomass (Jindal et al., 2008). The majority of terrestrial carbon is stored in tree trunks, branches, foliage, and roots, which are collectively referred to as biomass (Muradian et al., 2013; Suryawanshi et al., 2014). Unlike many plants and crops, forests can accumulate carbon over long periods, such as decades or centuries. Forest ecosystems store between 20 and 100 times more carbon per unit area compared to agricultural lands. (Brown & Pearce, 1994). In this way, forests play a crucial role in carbon sequestration, offering long-term potential for carbon storage as a sink. Estimating the total biomass and soil carbon stored in a forest is essential because it benefits the local population both economically and ecologically (Shrestha, 2009). The REDD+ program aims to reduce emissions from deforestation and forest degradation by improving forest carbon stock assessment and monitoring, supporting reforestation projects, and helping developing countries meet global climate goals through reward-based systems (Muradian et al., 2013). Since 2008, Nepal has made significant progress in preparing for REDD+. However, Nepal faces significant challenges to effective participation because there is limited research on the scientific methods for measuring carbon stocks, monitoring changes over time, and establishing baseline scenarios for emission reduction evaluation (Acharya et al., 2009). Nepal’s goal is to achieve net zero emissions between 2020 and 2030 and become entirely net Received: 22 September 2024 Revised: 7 August 2025 Accepted: 9 September 2025 Published: 30 September 2025 Banko Janakari, Vol 35 No. 2, 2025 Pp 16-24https://doi.org/10.3126/banko.v35i2.70006 https://orcid.org/0009-0005-3739-0377 https://orcid.org/0009-0007-4424-9405 https://orcid.org/0009-0009-6432-7954 https://orcid.org/0009-0000-4504-5614 https://orcid.org/0000-0003-3819-9062 17 Banko Janakari, Vol 35 No. 2 zero by 2045 (Pradhan et al., 2018; Shakya et al., 2023). The key to lowering carbon emissions is management that focuses on increasing forests’ role as carbon sinks. Numerous studies show that Nepal’s community- managed forests have significant potential for sequestering carbon (Carlson & Curran, 2009; Karky & Skutsch, 2010). Users of the forests are increasingly interested in learning about and utilizing the potential for carbon sequestration in this environment. Currently, more than 23000 Community Forest User Groups (CFUGs) have been established, representing 2.4 million households, or 35% of Nepal’s total population, and they are responsible for managing 24,90,194 hectares of national forest that can store carbon (MoFE, 2020). Hope remains that, over time, the financial resources to support countries like Nepal in implementing climate mitigation and adaptation strategies will become more accessible (UNFCCC, 2015). The geographical, physiographic, and cultural diversity of Nepal’s terrain is reflected in its mainly agricultural and forested landscape. Because of its extensive physiographic features and wide climatic variations, Ilam district is exceptionally diverse in its plant species. Many tree species can transform a large amount of atmospheric carbon dioxide into biomass. This provides multiple benefits, both directly and indirectly, by sequestering atmospheric carbon dioxide in biomass and helping to reduce climate change. Since temperate (Alnus, Castanopsis, and others) and tropical (Shorea robusta) forests both store and reduce carbon emissions, they can be key allies in the effort to fight rising atmospheric carbon dioxide levels. The capability of its forests to store atmospheric carbon can help determine potential compensation for countries that need to protect forests beyond their own needs. In Nepal, few studies directly focus on estimating carbon stocks in different forest categories. Research shows that carbon sequestration rates vary significantly among forest types and locations. For example, sub- tropical Sal forests in central Nepal sequester about 2.6 Mg ha-1 of carbon annually (Thapa-Magar & Shrestha, 2015). Similarly, riverine forests in the central tropical region and Alnus nepalensis forests in the central and western mid-hills have higher sequestration rates, ranging from 1.30 to 3.21 Mg ha-1per year (Baral et al., 2009). Still, information on carbon stocks across various forest ecosystems in Nepal remains limited. Considering different physiographic zones in studying biomass and carbon yields valid comparative results. Therefore, the study aims to measure biomass carbon in two forest types and compare their roles in offsetting atmospheric carbon. Materials and methods Study area The sites are located within two CFs in Ilam district (26°54′42.12″ N and 87°55′12.72″ E), Nepal: Pasupati Community Forest in Mai municipality, wards no. 1 & 2, and Deumai Namuna Community Forest in Deumai municipality, ward no. 1 (Figure 1). These two Community Forests represent the tropical and temperate regions. Pashupati Community Forest lies in the eastern tropical zone (200m-300m above mean sea level), while Deumai Namuna Community Forest is in the lower temperate zone (2100m-2700m above mean sea level). Pashupati Community Forest covers 200 hectares, and Deumai Namuna Community Forest spans 155.07 hectares. Tropical terai Sal (Shorea robusta) mixed hardwoods are the main tree species in Pashupati CF, whereas mixed species dominate in Deumai Namuna CF. Data collection Data collection for this study was based on the Community Forestry Inventory Guidelines (MoFSC, 2004). The data were collected using a stratified systematic sampling method with 1% sampling intensity. Stratification was conducted based on physical boundaries as documented in the Operational Plan of the forests, which divided the forest into different blocks. A total of 30 sampling plots were established in Deumai Namuna CF and 40 in Pashupati CF, with a consistent plot-to-plot distance of 224 meters. To measure the above-ground biomass of trees, poles, saplings, and seedlings, sample plots with concentric circular shapes and varying radii were selected and set up within the sampling area. A 12.61-meter radius was designated as the outermost plot to evaluate above-ground tree biomass (AGTB). Above-ground pole biomass (AGPB) was measured within the subsequent inner plot with a 5.64-meter radius. Similarly, a 2.82-meter radius inner plot was established for counting regeneration. In these sample plots, measurements of DBH at 1.3 meters and total heights of poles, trees, and saplings were taken using diameter tapes and Suunto clinometers. Poudel et al. 18 Banko Janakari, Vol 35 No. 2 Figure 1: Map of Study Area Data collection Data collection for this study was based on the Community Forestry Inventory Guidelines (MoFSC, 2004). The data were collected using a stratified systematic sampling method with 1% sampling intensity. Stratification was conducted based on physical boundaries as documented in the Operational Plan of the forests, which divided the forest into different blocks. A total of 30 sampling plots were established in Deumai Namuna CF and 40 in Pashupati CF, with a consistent plot-to-plot distance of 224 meters. To measure the above- ground biomass of trees, poles, saplings, and seedlings, sample plots with concentric circular shapes and varying radii were selected and set up within the sampling area. A 12.61-meter radius was designated as the outermost plot to evaluate above-ground tree biomass (AGTB). Above-ground pole biomass (AGPB) was measured within the subsequent inner plot with a 5.64-meter radius. Similarly, a 2.82-meter radius inner plot was established for counting regeneration. In these sample plots, measurements of DBH at 1.3 meters and total heights of poles, trees, and saplings were taken using diameter tapes and Suunto clinometers. Data analysis A simplified standard regression model incorporating DBH, height, and wood density was used to estimate tree biomass for calculating biomass and carbon stock according to the community forest carbon measurement guideline, which is based on average annual rainfall (Chave et al., 2005; Subedi et al., 2010). For species with unknown wood density, the empirical biomass equation developed by Zianis (2008) for global use was employed. (Cairns et al., 1997; Tamrakar, 2000) Where, AGSB = above-ground sapling biomass (kg); Log = natural logarithm a = intercept of sapling allometry (no unit) b = slope of sapling allometry (no unit) D = stem diameter (cm) Root to shoot ratios of 0.26 for the temperate region (Cairns et al., 1997) and 0.21 for lowland tropical forests (Malhi et al., 2014) were used to determine below-ground root biomass (BGRB). A default biomass-to-carbon conversion factor of 0.47 was employed to calculate carbon stock density. (IPCC, 2006). Overall, carbon was estimated by aggregating the carbon content from all distinct storage pools. Results Species richness The forest was more diverse in the temperate region than in the tropical region in the Ilam district. During the inventory, the mid-hill forest contained a greater number of species than the Chure forest. In Figure 1: Map of Study Area                                           (Chave et al., 2005).                      (Zianis, 2008) Where, AGTB = Above-ground Tree Biomass (kg); ρ = specific gravity of wood (g/cm3), D = dbh = diameter of the tree at breast height (cm); H = height of the tree (meters). a = 0.1424 and b= 2.3679 The aboveground biomass of saplings was estimated using a logarithmically transformed allometric formula (Tamrakar, 2000). Poudel et al. 19 Banko Janakari, Vol 35 No. 2 the field study, 22 species were recorded in Deumai Namuna CF, whereas 17 species were documented in Pashupati CF. Major species in Pashupati CF of the tropical zone included Shorea robusta (Sal), Terminalia alata (Saj), Schima wallichi (Chilaune), Lagerstroemia parviflora (Botdhayero), and Adina cordifolia (Karma). In Deumai Namuna CF of the temperate zone, dominant species were Castanopsis sp. (Kattus), Quercus semecarpifolia (Khasru), Alnus nepalensis (Utis), Rhododendron arboreum (Laligurans), and Quercus lamellosa (Bajrath) (see Figure 2 and Figure 3). CF had 44 trees and 103 poles per hectare, while Deumai Namuna CF had 55 trees and 193 poles per hectare. Shorea robusta was the dominant species in Pashupati CF, whereas Castanopsis indica was the main species in Deumai Namuna CF. There was considerable variation in average diameter (p=0.38, =0.05) and average height (p=0.20, =0.05) among major species both CFs. General statistics for diameter and height in the two CFs are shown in Tables 1 and 2. Table 1: Statistics of diameter and height of major species in Pashupati CF Species DBH (cm) Height (m) Average Minimum Maximum Average Minimum Maximum Shorea robusta 48.73 2.00 92.00 18.80 4.00 29.00 Terminalia alata 63.75 48.00 84.00 24.25 21.00 27.00 Schima wallichi 28.50 6.00 87.00 13.29 6.00 25.00 Lagerstormia parviflora 22.13 4.00 41.00 11.25 8.00 15.00 Adina cordifolia 70.00 51.00 93.00 21.50 15.00 25.00 Others 24.40 17.33 29.46 11.64 9.67 13.33 Overall 42.92 21.39 71.08 16.79 10.61 22.39 Table 2: Statistics of diameter and height of major species in Deumai Namuna CF Species DBH (cm) Height (m) Average Minimum Maximum Average Minimum Maximum Castanopsis indica 41.63 5.50 80.53 14.82 5.00 22.00 Quercus semecarpifolia 25.64 4.50 57.30 11.65 6.00 18.00 Alnus nepalensis 27.40 4.00 73.21 13.25 5.00 18.00 Rhododendron arboretum 29.30 6.00 56.02 11.69 7.00 15.00 Quercus lamellosa 55.64 9.00 89.13 17.38 8.00 22.00 Others 22.60 13.74 34.29 11.23 8.44 14.35 Overall 33.70 7.12 65.08 13.34 6.57 18.23 Biomass and carbon stock Table 3 shows the biomass stock density of the two different forest types. Table 3: Above-ground and below-ground biomass of CFs CF AGTB AGPB AGSB Total AGB BGB Total Biomass Total Carbon (Mg/ha) (Mg/ha) (Mg/ha) (Mg/ha) (Mg/ha) (Mg/ha) (Mg/ha) Deumai Namuna CF 94.50 34.02 5.88 134.40 34.94 169.34 79.59 Pashupati CF 144.41 18.66 3.99 167.05 35.08 202.14 95.00 Note: AGTB- Above-ground tree biomass, AGPB- Above-ground pole biomass, AGSB- Above-ground sapling biomass, AGB- Above-ground biomass, BGB- Below-ground biomass Carbon stock estimation Overall vegetation carbon stock was calculated by adding the above-ground biomass carbon and below-ground biomass carbon of the two forest regions, showing that the mean carbon Figure 2: Species richness in Pashupati CF was the dominant species in Pashupati CF, whereas Castanopsis indica was the main species in Deumai Namuna CF. There was considerable variation in average diameter (p=0.38, α=0.05) and average height (p=0.20, α=0.05) among major species both CFs. General statistics for diameter and height in the two CFs are shown in Tables 1 and 2. Biomass and carbon stock Table 3 shows the biomass stock density of the two different forest types. Carbon stock estimation Overall vegetation carbon stock was calculated by adding the above-ground biomass carbon and below- ground biomass carbon of the two forest regions, showing that the mean carbon density was higher in the tropical forest (95 Mg/ha) than in the temperate forest (75.59 Mg/ha) (Table 4). CF had 44 trees and 103 poles per hectare, while Deumai Namuna CF had 55 trees and 193 poles per hectare. Shorea robusta was the dominant species in Pashupati CF, whereas Castanopsis indica was the main species in Deumai Namuna CF. There was considerable variation in average diameter (p=0.38, =0.05) and average height (p=0.20, =0.05) among major species both CFs. General statistics for diameter and height in the two CFs are shown in Tables 1 and 2. Table 1: Statistics of diameter and height of major species in Pashupati CF Species DBH (cm) Height (m) Average Minimum Maximum Average Minimum Maximum Shorea robusta 48.73 2.00 92.00 18.80 4.00 29.00 Terminalia alata 63.75 48.00 84.00 24.25 21.00 27.00 Schima wallichi 28.50 6.00 87.00 13.29 6.00 25.00 Lagerstormia parviflora 22.13 4.00 41.00 11.25 8.00 15.00 Adina cordifolia 70.00 51.00 93.00 21.50 15.00 25.00 Others 24.40 17.33 29.46 11.64 9.67 13.33 Overall 42.92 21.39 71.08 16.79 10.61 22.39 Table 2: Statistics of diameter and height of major species in Deumai Namuna CF Species DBH (cm) Height (m) Average Minimum Maximum Average Minimum Maximum Castanopsis indica 41.63 5.50 80.53 14.82 5.00 22.00 Quercus semecarpifolia 25.64 4.50 57.30 11.65 6.00 18.00 Alnus nepalensis 27.40 4.00 73.21 13.25 5.00 18.00 Rhododendron arboretum 29.30 6.00 56.02 11.69 7.00 15.00 Quercus lamellosa 55.64 9.00 89.13 17.38 8.00 22.00 Others 22.60 13.74 34.29 11.23 8.44 14.35 Overall 33.70 7.12 65.08 13.34 6.57 18.23 Biomass and carbon stock Table 3 shows the biomass stock density of the two different forest types. Table 3: Above-ground and below-ground biomass of CFs CF AGTB AGPB AGSB Total AGB BGB Total Biomass Total Carbon (Mg/ha) (Mg/ha) (Mg/ha) (Mg/ha) (Mg/ha) (Mg/ha) (Mg/ha) Deumai Namuna CF 94.50 34.02 5.88 134.40 34.94 169.34 79.59 Pashupati CF 144.41 18.66 3.99 167.05 35.08 202.14 95.00 Note: AGTB- Above-ground tree biomass, AGPB- Above-ground pole biomass, AGSB- Above-ground sapling biomass, AGB- Above-ground biomass, BGB- Below-ground biomass Carbon stock estimation Overall vegetation carbon stock was calculated by adding the above-ground biomass carbon and below-ground biomass carbon of the two forest regions, showing that the mean carbon Table 1: Statistics of diameter and height of major species in Pashupati CF Table 2: Statistics of diameter and height of major species in Deumai Namuna CF Figure 3: Species richness in Deumai Namuna CF Forest type and status Tropical Sal (Shorea robusta) mixed hardwood and temperate mixed forest formed the significant part of the study area. Tree densities varied notably in the CFs examined. Pashupati CF had 44 trees and 103 poles per hectare, while Deumai Namuna CF had 55 trees and 193 poles per hectare. Shorea robusta Species Richness in Deumai Namuna CF Poudel et al. 20 Banko Janakari, Vol 35 No. 2 Figure 4: Aggregated stock (carbon) in varied carbon pools of differing forest regions Carbon stock distribution with respect to DBH class and height class In the tropical region, carbon stock was highest in the DBH class of 70-80 cm (26.52 Mg/ha), while in the temperate zone, the highest carbon stock was found in the 20-30 cm DBH class (14.15 Mg/ha). Similarly, the lowest amount of carbon stored was 0.83 Mg/ ha in the 30-40 cm DBH class of the tropical forest and 2.48 Mg/ha in the 0-10 cm DBH class of the temperate forest (Figure 5). Figure 5: Carbon Stock with respect to DBH class In Pashupati CF of the tropical zone, the highest carbon stock was in the 25-30 meter height class (38.77 Mg/ha), while in Deumai Namuna CF of the temperate zone, the highest carbon stock was in the 15-20 meter height class (31.78 Mg/ha). Similarly, the lowest stocking was found in the 0–5 m height class in both forests (Figure 6). Figure 6: Carbon Stock with respect to Height class. Carbon sequestered by different species In Pashupati CF, which is a tropical forest, Shorea robusta (Sal) contributed the highest amount of carbon sequestration with a carbon stock of 63.01%. It was followed by Adina cordifolia, Terminalia alata, Schima wallichi, Lagerstromia parviflora, T. chebula, and T. belerica, which accounted for 12.61%, 9.78%, 4.51%, 2.59%, 2.04%, and 0.58% of the total carbon stock from trees, poles, and saplings, respectively. Similarly, other species contributed for 4.87% to carbon sequestration (Figure 7). In Deumai Namuna CF, i.e., temperate forest, Castanopsis sp. (katus) stored the highest amount of carbon at 33.19%, followed by Quercus lamellosa, Q. semecarpifolia, Alnus nepalensis, Rhododendron arboretum, Symplocos theifolia, and Michelia sp. (Chanp), which sequestered 17.80%, 9.08%, 6.86%, 4.87%, 3.42%, and 1.46% of the total carbon stored by trees, poles, and saplings, respectively. Similarly, other species accounted for 27.33% of carbon sequestration (see Figure 8). Carbon stocks comparison between tropical and temperate forests The recorded carbon stock values from sample plots were analyzed to compare tropical and temperate CF had 44 trees and 103 poles per hectare, while Deumai Namuna CF had 55 trees and 193 poles per hectare. Shorea robusta was the dominant species in Pashupati CF, whereas Castanopsis indica was the main species in Deumai Namuna CF. There was considerable variation in average diameter (p=0.38, =0.05) and average height (p=0.20, =0.05) among major species both CFs. General statistics for diameter and height in the two CFs are shown in Tables 1 and 2. Table 1: Statistics of diameter and height of major species in Pashupati CF Species DBH (cm) Height (m) Average Minimum Maximum Average Minimum Maximum Shorea robusta 48.73 2.00 92.00 18.80 4.00 29.00 Terminalia alata 63.75 48.00 84.00 24.25 21.00 27.00 Schima wallichi 28.50 6.00 87.00 13.29 6.00 25.00 Lagerstormia parviflora 22.13 4.00 41.00 11.25 8.00 15.00 Adina cordifolia 70.00 51.00 93.00 21.50 15.00 25.00 Others 24.40 17.33 29.46 11.64 9.67 13.33 Overall 42.92 21.39 71.08 16.79 10.61 22.39 Table 2: Statistics of diameter and height of major species in Deumai Namuna CF Species DBH (cm) Height (m) Average Minimum Maximum Average Minimum Maximum Castanopsis indica 41.63 5.50 80.53 14.82 5.00 22.00 Quercus semecarpifolia 25.64 4.50 57.30 11.65 6.00 18.00 Alnus nepalensis 27.40 4.00 73.21 13.25 5.00 18.00 Rhododendron arboretum 29.30 6.00 56.02 11.69 7.00 15.00 Quercus lamellosa 55.64 9.00 89.13 17.38 8.00 22.00 Others 22.60 13.74 34.29 11.23 8.44 14.35 Overall 33.70 7.12 65.08 13.34 6.57 18.23 Biomass and carbon stock Table 3 shows the biomass stock density of the two different forest types. Table 3: Above-ground and below-ground biomass of CFs CF AGTB AGPB AGSB Total AGB BGB Total Biomass Total Carbon (Mg/ha) (Mg/ha) (Mg/ha) (Mg/ha) (Mg/ha) (Mg/ha) (Mg/ha) Deumai Namuna CF 94.50 34.02 5.88 134.40 34.94 169.34 79.59 Pashupati CF 144.41 18.66 3.99 167.05 35.08 202.14 95.00 Note: AGTB- Above-ground tree biomass, AGPB- Above-ground pole biomass, AGSB- Above-ground sapling biomass, AGB- Above-ground biomass, BGB- Below-ground biomass Carbon stock estimation Overall vegetation carbon stock was calculated by adding the above-ground biomass carbon and below-ground biomass carbon of the two forest regions, showing that the mean carbon Table 3: Above-ground and below-ground biomass of CFs Table 4: Carbon stock in tropical and temperate forests density was higher in the tropical forest (95 Mg/ha) than in the temperate forest (75.59 Mg/ha) (Table 4). Table 4: Carbon stock in tropical and temperate forests CFs Aboveground Carbon stock (Mg/ha) Belowground Carbon Stock (Mg/ha) Total Carbon Stock (Mg/ha) Pashupati CF 78.51 16.49 95 Deumai Namuna CF 63.17 16.42 75.59 Figure 4: Aggregated stock (carbon) in varied carbon pools of differing forest regions Carbon stock distribution with respect to DBH class and height class In the tropical region, carbon stock was highest in the DBH class of 70-80 cm (26.52 Mg/ha), while in the temperate zone, the highest carbon stock was found in the 20-30 cm DBH class (14.15 Mg/ha). Similarly, the lowest amount of carbon stored was 0.83 Mg/ha in the 30-40 cm DBH class of the tropical forest and 2.48 Mg/ha in the 0-10 cm DBH class of the temperate forest (Figure 5). Figure 5: Carbon Stock with respect to DBH class. Poudel et al. 21 Banko Janakari, Vol 35 No. 2 forests. Welch’s t-test showed no significant statistical differences in average carbon stock between the two forest types (t = 1.771, df = 63, p = 0.0814). Additionally, no significant relationship was found between carbon stock and diameter class. (t = 0.498, p = 0.6291) or height class (t = 0.01, p = 0.993) within either forest type (Table 5). These results suggest that variations in diameter and height classes do not significantly affect carbon stock differences between tropical and temperate forests. Discussions Biomass and carbon stock were higher in tropical forest than in temperate forests. As diameter increased , the biomass of the tree was also increased, indicating a direct positive relationship between DBH and biomass across tree components (Supriya Devi & Yadava, 2009). The amount of aboveground biomass in a forest is influenced by factors such as forest age, tree density, species type, and wood density (Shrestha & Devkota, 2013; Zhang et al., 2013; Sun et al., 2016). Therefore, the higher biomass value in the tropical region was due to the prevalence of older trees with larger diameters and greater heights. Additionally, tropical regions contained species with higher wood densities. Despite higher stem density in the temperate region, biomass was lower, as increased stem density does not necessarily lead to greater tree biomass (Khadanga & Jayakumar, 2020). Overall, forest biomass is considered an essential primary source of carbon stock. The total biomass of the tree component was 169.34 Mg/ha in CFs of Chure (tropical) and and 202.14 Mg/ha in the mid-hill (temperate) regions. Shrestha (2009) reported a similar biomass amount of 183.29 Mg/ha in Shorea robusta forests, while the Schima-Castanopsis Forest studied had a much lower biomass of 80.4 Mg/ha. The Forest Resource Assessment published by DFRS in 2015 showed that the average aboveground biomass of Nepal is 172.21 Mg/ha in Chure and 143.26 Mg/ha the Mid- Hill regions, which aligns with this study. Baral et al. (2009) observed that the above-ground carbon content of Shorea robusta forests in the Mahabharat foothills was higher at 97.86 Mg/ha, while the Schima-Castanopsis and Alnus nepalensis forests had 76.24 Mg/ha and 76 Mg/ha, respectively. However, these data are from central Nepal, where variations in elevation, stand age, soil, and climate can influence the amount of carbon stored by the forests (Shrestha & Singh, 2008; Dar & Sundarapandian, 2015; Thapa-Magar & Shrestha, 2015). This study found that both forests sequester nearly equal amounts of carbon in their tree components. This result closely matches the national inventory carried out by the Department of Forest Research and Survey (DFRS, 2015), which reported an average carbon stock of 97.69 Mg/ha in the Chure region and 79.42 Mg/ha in the Middle Mountains. In contrast, Mandal et al. (2013) estimated an aboveground carbon stock of 116.72 Mg/ha and a belowground carbon stock of 15.12 Mg/ha in Mahottari District, which differs from the findings of this study. Figure 8: Carbon stock percentage in different species of temperate forest In Deumai Namuna CF, i.e., temperate forest, Castanopsis sp. (katus) stored the highest amount of carbon at 33.19%, followed by Quercus lamellosa, Q. semecarpifolia, Alnus nepalensis, Rhododendron arboretum, Symplocos theifolia, and Michelia sp. (Chanp), which sequestered 17.80%, 9.08%, 6.86%, 4.87%, 3.42%, and 1.46% of the total carbon stored by trees, poles, and saplings, respectively. Similarly, other species accounted for 27.33% of carbon sequestration (see Figure 8). Carbon stocks comparison between tropical and temperate forests The recorded carbon stock values from sample plots were analyzed to compare tropical and temperate forests. Welch�s t-test showed no significant statistical differences in average carbon stock between the two forest types (t = 1.771, df = 63, p = 0.0814). Additionally, no significant relationship was found between carbon stock and diameter class. (t = 0.498, p = 0.6291) or height class (t = 0.01, p = 0.993) within either forest type (Table 5). These results suggest that variations in diameter and height classes do not significantly affect carbon stock differences between tropical and temperate forests. Table 5: Carbon stocks comparison between tropical and temperate forest S.N. Forest Test Parameters t-value P-value 1 Tropical Carbon stock vs. Diameter Class 0.498 0.6291 Temperate 2 Tropical Carbon stock vs. Height Class 0.01 0.993 Temperate Discussions Figure 7: Carbon stock percentage in different species of tropical forest Figure 8: Carbon stock percentage in different species of temperate forest Table 5: Carbon stocks comparison between tropical and temperate forest Poudel et al. 22 Banko Janakari, Vol 35 No. 2 Shorea robusta had the most extensive carbon stock in tropical forests among the species studied. Chand et al. (2018) noted that Shorea robusta had the highest carbon pool among forest species. They also reported that carbon stock was higher in larger DBH classes (>80 cm and 70-80 cm) in the tropical region, which aligns with this study. However, in the temperate region, the highest carbon stock was found in the 20-30 cm diameter class, consistent with the forests of Golapara District, Assam (Rabha, 2014). In the temperate region, Castanopsis sp. sequesters the highest amount of carbon, and concluded that Castanopsis contributed the highest amount of carbon in the forest due to its dominance (Tripathi et al., 2018). Overall, the carbon pool in tropical Shorea robusta-dominated forests was higher than in temperate Castanopsis-Quercus forests. It is reported that both biomass and carbon stock decrease with increasing altitude (Moser et al., 2007; Sheikh et al., 2012). Although in some cases, carbon storage shows a positive correlation with altitude (Alves et al., 2010; Pragasan, 2022). Conclusion As a source of biomass and an essential carbon sink, tropical forests play a crucial role in addressing the world’s environmental crisis. The carbon stored in forests showed variation across altitude, forest type, age, and wood density. Tropical forests store relatively more biomass carbon than temperate forests, due to the abundance of trees with larger diameters and heights. However, the temperate forests were more diverse than the tropical forests of Ilam district. No significant statistical differences were reported in the carbon accumulated by these forests in terms of diameter and height classes. Additionally, the presence of hardwood species with higher wood-specific gravity in tropical forests resulted in greater carbon stock. The study indicates that CFs in Nepal sequester a substantial amount of carbon, which may benefit future REDD+ initiatives. However, this research was limited to the biomass and carbon reservoirs of both temperate and tropical forests. Estimation of soil organic carbon was not included, even though soil contains a significant amount of carbon. This omission could affect the accuracy of the total carbon stock estimated in these forests. Broader studies covering larger geographical areas and diverse ecological zones are necessary to understand these findings better. Further research should also focus on soil organic carbon to enable stronger conclusions. Acknowledgements We would like to acknowledge the Division Forest Office, Illam, for their support during the fieldwork. We are also grateful to Mr. Siddhartha Regmi for his guidance during the initial draft of the manuscript. Author’s contribution AP: Conceptualization, methodology, field work, validation, formal analysis, writing original draft, writing review & editing; KPD: Conceptualization, methodology, formal analysis, writing review & editing; supervision; MJ: Methodology, field work, formal analysis, writing review & editing; STM: Methodology, formal analysis, writing review & editing; RK: Methodology, validation, formal analysis, writing original draft, writing review & editing, correspondence. Conflict of interests The authors declare no conflict of interests. References Acharya, K. P., Dangi, R. B., Tripathi, D. M., Bushley, B. R., Bhandary, R. R., & Bhattarai, B. (2009). 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