Carbon and Canopy: Understanding Tree Diversity and Biomass in a Semi-Evergreen Forest of the Western Ghats

Tropical evergreen forests are the emerald hearts of biodiversity, and the Western Ghats of India are among the world's most celebrated biological hotspots. Stretching parallel to the west coast of India, this mountainous region harbors exceptional ecological wealth, much of it endemic—found nowhere else on Earth. However, despite its rich tapestry of life and relatively extensive forest cover, this region suffers from an acute lack of comprehensive, long-term ecological monitoring.

As of now, only nine Long-Term Monitoring (LTM) plots have been established in the Western Ghats: eight in evergreen and one in deciduous forests. Critically, tropical semi-evergreen forests (TSEF) are a unique and ecologically significant forest type but remain underrepresented in these efforts. These forests form a transitional zone between moist deciduous and evergreen formations and are often overlooked in conservation planning. To bridge this gap, researchers established a 1-hectare LTM plot in the Netravali region of the central Western Ghats and conducted an intensive inventory of woody species and forest structure following internationally standardized protocols. The work by Prof. Rajiv Kumar Chaturvedi & team from the Department of Humanities & Social Sciences, K K Birla Goa Campus, presents a snapshot of how these forests function, how they may persist and what needs to be conserved. This detailed ecological study, focused on three key aspects:

• Woody species diversity

• Forest structural characteristics

• Above-ground biomass and carbon stock

Why Woody Species and LTM Plots Matter

Woody species that are primarily trees and shrubs with persistent, woody stems form the structural backbone of forests. Monitoring these species over time provides valuable insight into ecosystem health, carbon sequestration potential, and long-term biodiversity trends. Long-Term Monitoring (LTM) plots allow researchers to track growth, mortality, recruitment (new tree establishment), and ecological shifts over decades which helps to form a critical baseline in an era of climate and land-use change.

The Netravali plot follows the Centre for Tropical Forest Science (CTFS) protocol, a globally recognized standard in tropical forest monitoring. Every woody individual with a diameter at breast height (DBH) ≥1 cm was tagged, identified, and measured which is a level of detail that reveals the forest's structure from seedlings to towering canopy trees. Additionally, tree data such as girth, basal area and height was also collected. 

Diversity in the Netravali Plot: A Rich Repository

The plot recorded 84 woody species, including 11 species endemic to the Western Ghats, an exceptionally high diversity for a single hectare and well above global averages for comparable forests. These 84 species span across 45 angiospermic families and 73 genera. Species from families such as Lauraceae, Euphorbiaceae, and Rubiaceae were well represented, echoing patterns seen in other parts of the Ghats. This high species richness affirms the ecological importance of the TSEF, which blends species typical of both evergreen and deciduous systems.

The tree density stood at 5,395 individuals per hectare, including 866 adult trees, reflecting a dense, dynamic, and maturing forest. These adult trees contributed a basal area of 33.6 m² per hectare, a measurement that exceeds the pantropical average of 32 m² ha⁻¹ which indicates a structurally well-developed forest with substantial biomass.

To quantify diversity, the study used established ecological indices. The Simpson Index, which estimates the probability that two individuals randomly selected from the sample belong to different species, yielded a high value of 0.92. This suggests that there is a very low chance of selecting the same species twice, highlighting substantial species richness. In parallel, Shannon’s Diversity Index, which accounts for both abundance and evenness of species, was calculated at 3.19. These high values indicate a community with not just many species, but with a relatively even distribution of individuals among those species.

Regeneration and Forest Health: Reading the Patterns

A critical aspect of forest sustainability is regeneration—the natural replacement of older trees through seedlings and saplings. The Netravali plot displayed an inverted J-shaped diameter distribution, a classic signal of healthy regeneration. This distribution is characterized by a large number of individuals in smaller size classes and progressively fewer in larger ones which reflects a dynamic, self-sustaining forest.

The dominant tree species in the plot were well-represented across all developmental stages- from seedlings to mature trees. This broad presence suggests that key species are successfully reproducing and establishing themselves, therefore indicating strong regeneration potential and ecological stability. However, the study also flagged areas of concern. Six species were found exclusively in the adult stage, raising red flags about their long-term viability in the absence of younger cohorts. Among these, Eugenia macrosepala, a species endemic to the Western Ghats stood out due to its complete lack of regeneration. This finding elevates it to a conservation priority, as the absence of seedlings or saplings suggests it may be at risk of local decline or extinction without targeted intervention. This points to possible vulnerabilities—whether due to habitat specificity, seed dispersal challenges, or environmental pressures—that may necessitate targeted conservation efforts.

A Storehouse of Carbon: Biomass and Soil Metrics

Tropical forests are pivotal in climate regulation due to their ability to store vast amounts of carbon. The Netravali forest plot was found to have an aboveground biomass (AGB) of 289.4 megagrams per hectare (Mg ha⁻¹), with a total carbon stock of 241.75 MgC ha⁻¹. These values fall well within the global range reported for tropical semi-evergreen forests and highlight their role in mitigating atmospheric carbon levels.

The forest’s soil organic carbon (SOC) was estimated at 79.4 MgC ha⁻¹, consistent with values for Asian tropical forests, suggesting a healthy, functioning soil ecosystem. Together, these carbon stocks, both above and below ground, reinforce the importance of conserving such forest types for biodiversity, climate resilience and ecological balance.

Implications and the Way Forward

This study is more than just a catalogue of trees—it is a strategic call to expand long-term monitoring in ecologically vital but understudied regions. The Netravali plot offers a critical benchmark for TSEFs, which until now had remained largely unmonitored in the Western Ghats. Its high diversity, strong regeneration indicators, and above-average carbon stocks all make a compelling case for increased conservation investment. Moreover, the inclusion of endemic species with limited regeneration points to the need for species-specific studies and potentially restoration initiatives to support vulnerable populations.

Conclusion: Preserving a Living Laboratory

The Western Ghats are often described as a living laboratory of evolution, where ancient lineages and modern ecological dynamics coexist. The Netravali LTM plot meticulously documents woody species diversity, structural dynamics, carbon storage, and regeneration to provides an essential reference for ongoing and future research. In an era where biodiversity is declining globally and forest ecosystems are under unprecedented stress, such data-rich studies offer hope and direction. They remind us that well-managed, biodiverse forests like those in the Western Ghats are not just passive repositories of life—but active guardians of our planet’s future.