Present results highlight notable differences in forest structural characteristics including biomass distribution across various forest types. These findings offer valuable insights into the ecological processes and management implications within these environments. Differences in tree density and basal area among forest types underscore the unique ecological conditions and species compositions that define each ecosystem (Schall et al. 2018). Oak forests exhibit greater tree density and basal area compared to deodar, sal and pine forests, indicating a potential for increased biodiversity and productivity within oak-dominated ecosystems. The observed tree density, ranging from 620 to 920 individuals per hectare, aligns with previous reports from the central Himalayan forests (Garkoti 2007). Our study underscores the significant influence of vegetation type, species composition, and girth class on overall biomass and carbon sequestration within distinct forest ecosystems. The basal area of trees is typically affected by factors such as density, stand age, site index, and crown size (Berrill et al. 2016). Our findings indicate a decrease in basal area and DBH in pine forests, likely due to the prevalence of younger tree species, suggesting ongoing forest development (Liang et al. 2007). These results highlight the substantial contribution of dominant species to overall forest density, reflecting both ecological adaptation and species-specific growth patterns in various forest environments in the central Himalaya. The biomass distribution across diameter classes reveals unique growth patterns and successional dynamics within various forest types (Piponiot et al. 2022). The highest tree density and basal area values, recorded within the 30–70 cm DBH (diameter at breast height) range, suggest that medium-sized trees dominate the forest structure. This indicates a forest in a mid-successional stage where trees have grown past the sapling stage but have not yet reached their maximum potential size. Lower values in the 10–20 cm DBH range could indicate fewer young, regenerating trees, potentially suggesting limited recent regeneration or high competition and mortality rates among smaller trees. Conversely, the lowest values in the greater than 90 cm DBH category indicate few large, old-growth trees. This may imply a history of disturbance, such as logging or natural events (e.g., landslides, fires), preventing trees from reaching their maximum size. In deodar and oak forests, the prevalence of larger diameter classes indicates mature stands with substantial biomass accumulation over time, likely due to favorable growth conditions and effective management strategies. Deodar forest is known for its large size trees and longevity, contributing to higher biomass accumulation. These forests likely have a dense canopy and significant carbon sequestration capacity, highlighting their ecological importance in carbon storage and climate regulation (Sharma et al. 2010). The elevated aboveground and belowground biomass levels in these forests highlight their significance as carbon sinks and contributors to ecosystem services. The conservation of these forest ecosystems is imperative, considering their pivotal role in mitigating climate change and providing habitats.
In contrast, pine and sal forests demonstrated comparatively lower tree biomass (128 and 149.12 Mg ha− 1, respectively) compared to the findings of Verma and Garkoti (2019) and Pandey et al. (2023), possibly due to a prevalence of smaller individuals in lower girth classes. This reduced biomass suggests potential anthropogenic pressures or natural disturbances affecting biomass productivity and carbon sequestration capacity in these ecosystems. The higher biomass observed in deodar and oak forests may be attributed to their elevated tree density and reduced anthropogenic pressure. The distribution of biomass across nine DBH classes revealed that the lower DBH classes (30–60 cm) had a larger biomass allocation, likely due to their higher densities and basal areas. Previous studies conducted in the Himalayan region (Sharma et al. 2010) and globally (Dyola et al. 2022) have also highlighted the influence of forest stand attributes on carbon stock in various forest types.
The primary role of aboveground biomass (AGBD) in total biomass stock remains consistent across various forest types. Below-ground biomass density (BGBD) and its proportional contribution (18–25%) to the total biomass stock play a significant part in below-ground carbon storage across these forest types. There is notable variability in total tree biomass carbon, including aboveground and belowground biomass, among forest types. Pine forests exhibit the lowest total tree biomass carbon, while deodar forests have the highest. This divergence likely stems from differences in tree species composition, density, and growth rates among these forests (Singh and Singh 1992).
Certain tree species contribute more substantially to carbon stocks within each forest type than others. For instance, C. deodara (deodar) in deodar forests, Q. leucotrichophora (oak) in oak forests, S. robusta (sal) in sal forests, and P. roxburghii (pine) in pine forests are identified as species with higher carbon stocks. This highlights the importance of considering species composition in forest carbon stock assessments. Additionally, in mixed forests, the relative contributions of dominant and co-dominant species vary according to the composition of the forest, aligning with findings from previous studies (Kaushal and Baishya 2021).
Soil bulk density (BD) measures soil compaction and porosity, affecting root penetration, water infiltration, and gas exchange. The highest average bulk density found in the sal forest (1.31 g cm⁻³) suggests that the soil in this forest is more compact than the others, which can restrict root growth and reduce water infiltration. Higher total nitrogen and phosphorus contents in oak and deodar forests reflect the nutrient-rich conditions in these forests. The higher TN and TP might be due to greater leaf litter and organic matter decomposition in these forests, enhancing the nutrient cycling process. These conditions are conducive to supporting diverse and dense vegetation. The interplay of these soil properties creates distinct ecological niches and influences each forest type's species composition and structure (Rawat 2005). The variations in soil texture and nutrient content also dictate the type of microbial communities and soil fauna, further influencing decomposition rates and nutrient cycling. The study results also evaluated soil organic carbon (SOC) stocks across forest types, uncovering significant differences. Particularly, oak forests displayed the highest SOC stocks, in contrast to pine forests, which showed the lowest levels. This suggests that soil carbon storage is influenced by various factors, such as litter decomposition rates, microbial activity, and soil texture, which vary across diverse forest ecosystems (Lange et al. 2015). Furthermore, the research indicates that forest growth and increased litterfall over time could contribute to restoring soil carbon stocks and cycling (Feng et al. 2019). These findings are consistent with prior studies suggesting that biomass distribution and carbon stocks within forest ecosystems vary based on factors like forest types, stand age, species compositions and soil properties, supporting our conclusions (Zhou et al. 2023).
Differences in litter and understory biomass among different forest types arise from variations in litter decomposition rates, understory vegetation dynamics, and nutrient cycling processes (Joshi and Garkoti 2023c). The carbon content of litter is influenced by several factors, including tree type, litter production, decomposition rate, and microenvironment (Xiao et al. 2019). The carbon amount in litter reported for all forest types falls within the documented range from various studies (Neumann et al. 2018).
The distribution of carbon across various ecosystem components such as vegetation, dead wood, litter, understory, and soil varied across different forest types. For instance, oak forests tended to allocate more carbon to aboveground biomass and soil. In contrast, pine forests exhibited a higher allocation to aboveground biomass with relatively less soil. These variations likely stem from differences in vegetation structure, litter quality, and decomposition rates among forest types (Garkoti 2011). Notably, regardless of these disparities in carbon allocation, soil organic carbon consistently emerged as the predominant contributor to total ecosystem carbon across all forest types. This underscores the significance of soil carbon storage in overall carbon sequestration, thereby emphasizing role of forests as vital carbon sinks. This observation has been supported by multiple studies (Sharma et al. 2010; Joshi and Garkoti 2021b).
The study reveals that altitude, slope, tree density, and total basal area significantly influence carbon storage in AGBD, BGBD, dead wood, litter, and understory. These factors shape the structural characteristics of forests and influence processes such as photosynthesis, respiration, and decomposition. The Mantel test results indicate that environmental factors significantly influence changes in carbon storage, highlighting the need to consider multiple ecological variables when studying carbon dynamics. The significant correlations identified through correlation analysis highlight the interdependence of ecosystem components and environmental conditions. The strong correlation between SOC and TN underscores their synergistic role in soil fertility and carbon storage, which also influences soil pH, EC, and WHC, demonstrating the interconnected nature of soil properties. These findings stress that carbon storage in ecosystems is a multifactorial process, with various environmental factors interacting to influence carbon dynamics (Song et al. 2024). Understanding these relationships is crucial for developing effective carbon management strategies and predicting ecosystem responses to environmental changes.
The research outcomes reveal that oak forests exhibit the highest capacity for sequestering carbon dioxide equivalents (CO2e) per hectare, followed by deodar, sal, and pine forests, in a descending sequence. The valuation of carbon credits for primary forest types within the central Himalayan region is influenced by a blend of ecological dynamics, management practices, and methodological considerations (Negi 2022). This implies that oak forests possess superior abilities to absorb and retain carbon from the atmosphere compared to other forest types scrutinized. For instance, oak forests are distinguished by their dense canopies and extensive root systems, potentially contributing to their elevated carbon sequestration rates (Joshi and Garkoti 2023a). Conversely, pine forests, which typically demonstrate lower carbon storage capacities, may feature less dense canopies and shallower root systems. Carbon credits are financial instruments denoting a reduction in greenhouse gas emissions, typically quantified in metric tons of CO2e (Babbar et al. 2021).
Consequently, forests exhibiting higher carbon sequestration capabilities can produce more carbon credits, which can be traded on carbon markets to incentivize forest conservation and reforestation efforts (Roy and Bhan 2024). The results show that oak forests have highest potential for carbon credit, followed by deodar, sal, and pine forests. This underscores the potential economic benefits of investing in the conservation and revitalization of oak forests, in addition to their environmental importance. The findings also reveal that oak forests in the central Himalayan region sequester the highest amount of CO2 equivalents per hectare, followed by deodar, sal, and pine forests. Consequently, oak forests are identified as the top generators of carbon credits, with deodar, sal, and pine forests ranking next.
These findings suggest prioritizing oak forests for climate change mitigation strategies in the central Himalayan region (Chakraborty et al. 2018). Protecting and enhancing the health of oak forests can maximize carbon sequestration and carbon credit generation, significantly contributing to global climate change mitigation efforts (Di Sacco et al. 2021). It is crucial to advocate for policy frameworks that incentivize oak forest conservation and sustainable management, such as payments for ecosystem services, carbon pricing mechanisms, and REDD + initiatives. Such supportive policies can create economic incentives for forest conservation while addressing climate change concerns