🌿 ecology

Restoration of tropical dry evergreen forest in southern India: balancing carbon sequestration with biodiversity conservation

This study demonstrates that restoring tropical dry evergreen forests in southern India with native species can achieve carbon sequestration levels comparable to non-native trees while maintaining high biodiversity, proving that ecological integrity and climate mitigation goals can be successfully balanced.

Original authors: Shanmugam, M., Pulla, S., Epinal, L. N.

Published 2026-07-10

📖 4 min read☕ Coffee break read

CC BY 4.0

Original authors: Shanmugam, M., Pulla, S., Epinal, L. N.

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ⚕️ This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer

Imagine a forest that started as a dusty, barren wasteland in 1973, looking more like a desert than a jungle. Back then, the only way to stop the wind and dirt was to plant fast-growing, non-native trees—think of them as the "speed demons" of the plant world, like Acacia auriculiformis and Eucalyptus. They grew up quickly, acting like a temporary shield. But starting in the early 1990s, the goal shifted. The team wanted to bring back the original, native Tropical Dry Evergreen Forest (TDEF), a unique and rare type of forest found only in specific parts of India. They began swapping the speed demons for native species, hoping to restore the ecosystem's true soul.

The big question was: Can these native trees, which were planted more recently and are currently shorter, ever catch up to the carbon-storing power of the fast-growing non-natives? Or do we have to choose between saving the planet's carbon and saving the planet's biodiversity?

The Great Carbon Race

The researchers took a deep dive into two restored forest patches in Auroville, India. They counted every single tree with a trunk thicker than a dinner plate (10 cm girth) across 36 different plots. The results were a mix of "wow" and "wait a minute."

First, the biodiversity win: The forest is now a bustling city of plants, hosting 91 native species from 34 different families. That's a huge party of native life!

But when it came to the "carbon bank account" (measured as Aboveground Biomass, or AGB), the non-native trees were currently winning the race. The total carbon stored in the trees averaged 66.91 ± 41.2 Mg ha⁻¹. While that's a solid amount, the non-native trees held the bag. Why? Because they are taller and have bigger trunks right now. In fact, in the larger tree size classes, the non-natives held nearly double the carbon of the natives.

The "Speed vs. Stamina" Analogy

Think of the non-native trees like sprinters. They started the race early (planted in the 70s), ran fast, and are currently way ahead. The native trees are like marathon runners who started later (in the 90s). They are currently shorter and smaller, but here is the twist: the paper suggests that if you look at how height grows relative to trunk thickness, the natives have the same "engine" as the non-natives.

The data shows that while the non-natives are currently taller, the native species have comparable wood density and the potential to grow just as tall as they get bigger. The authors suggest that as the old non-native trees eventually die and the native trees continue to grow, the native species could sequester carbon at levels similar to the non-natives in the long run. It's not a guarantee of a win yet, but the native trees are showing they have the stamina to catch up.

The Diversity Myth

Here is where the paper rules out a popular idea. Many scientists believe that the more different species you have in a forest, the more carbon it will store (like having a diverse team makes a company more productive). The researchers tested this by checking if the plots with more species had more carbon.

The result? Nope. They found no link between the number of species and the amount of carbon stored. Whether a plot had a few species or many, the carbon levels didn't change based on diversity alone. The paper explicitly states that in this specific restored forest, having more species didn't automatically mean more carbon. It suggests that in these young, recovering forests, the identity of the specific trees (like the dominant non-native Acacia) matters more than just the sheer number of different types.

The Bottom Line

So, what's the verdict? The paper suggests that restoring native TDEFs is a winning strategy for biodiversity, creating a rich home for 91 native species. While the non-native trees currently hold more carbon because they are older and taller, the native trees are not "carbon losers." They have the same wood density and growth potential, meaning they could store just as much carbon in the future.

The forest is a work in progress. The native trees are still growing into their potential, and while they haven't overtaken the non-natives in carbon storage yet, the authors suggest they are on track to do so. The forest proves you don't have to sacrifice biodiversity to store carbon; you just might have to be patient while the native marathon runners catch their stride.

Technical Summary: Restoration of Tropical Dry Evergreen Forest in Southern India

Problem Statement
Tropical dry evergreen forests (TDEFs) are a unique, highly threatened forest type confined to specific regions in Asia, including the southeastern coast of India. Historically, these forests have been largely converted to other land uses due to high human population densities, leaving only isolated patches. While global restoration efforts often prioritize fast-growing, non-native tree species for rapid carbon sequestration and economic gain, there is a recognized need to shift toward natural, high-diversity ecosystems that offer superior resilience and biodiversity conservation. However, a critical data gap exists regarding the carbon sequestration potential of restored TDEFs, specifically how native species compare to the non-native species traditionally favored in plantations. Furthermore, it remains unclear whether the positive relationship between plant species diversity and aboveground biomass (AGB), observed in other ecosystems, holds true in restored TDEFs.

Methodology
The study was conducted in Auroville, southern India, on a site that transitioned from a barren landscape in 1973 to a restored TDEF. Initial afforestation in 1973 utilized non-native species (e.g., Acacia auriculiformis, Eucalyptus globulus) for windbreaks. Since the early 1990s, the focus shifted to restoring native TDEF species, allowing for natural regeneration and the replacement of non-natives.

The researchers established 36 vegetation plots (20 m × 20 m, with some rectangular adaptations for steep terrain) across two sites: Pitchandikulam Forest (30 ha) and New Land-Ravena Forest (43 ha). All woody plants with a girth at breast height (GBH) ≥ 10 cm were identified, and their diameter at breast height (DBH) and height were measured.

Key analytical steps included:

Classification: Species were categorized as native or non-native based on geographical range data from the Plants of the World Online Portal.
Diversity Metrics: Plot-level species richness, Shannon index, Simpson index, and Hill numbers were calculated.
Biomass Estimation: Aboveground biomass (AGB) was estimated using the allometric equation $AGB = 0.0673 \times (\rho D^2 H)^{0.976} \times 0.001$ , where $\rho$ is wood density, $D$ is DBH, and $H$ is height. Carbon fractions were applied to derive aboveground and belowground carbon stocks.
Statistical Analysis: Welch's two-sample t-tests compared native and non-native groups regarding abundance, AGB, wood density, basal area, and height. Linear regressions tested the relationship between AGB and diversity indices. Height-DBH scaling relationships were modeled to project future carbon storage potential.

Key Results

Biodiversity: The restored site supports high woody-plant diversity, containing 1947 individuals across 117 species (34 families). Of these, 91 species (1002 individuals) are native, while 26 species (945 individuals) are non-native. Native species exhibited higher diversity indices than non-native species.
Carbon Stocks: The mean Aboveground Biomass (AGB) was 66.91 ± 41.2 Mg ha⁻¹, with total carbon (above- and below-ground) at 40.09 ± 25.7 Mg ha⁻¹. This magnitude is comparable to seasonally dry tropical forests globally.
Native vs. Non-Native Performance:
- Non-native species currently dominate the larger size classes (≥ 20 cm DBH), contributing nearly double the AGB of native species in these classes.
- This biomass advantage is driven by non-native species being significantly taller and having a larger basal area, rather than differences in wood density, which was comparable between groups.
- Native species, having been planted more recently, are generally shorter but show a population structure (reversed J-shape) indicating a growing cohort.
Scaling and Future Potential: Height-DBH modeling revealed that while non-native species are taller at small DBH values, the height difference diminishes as DBH increases. Given comparable wood densities, native species are predicted to reach heights and carbon storage levels similar to non-natives as they mature.
Diversity-Biomass Relationship: Contrary to the hypothesis, no significant relationship was found between plot-level AGB and species richness, Shannon index, or Simpson index.

Significance and Claims
The paper argues that restoring native TDEF species can achieve carbon storage levels comparable to non-native plantations in the long term, while simultaneously maintaining ecological integrity and high biodiversity. The study demonstrates that native species, despite being younger and currently shorter, possess the physiological capacity (wood density and height scaling) to sequester carbon at levels similar to commercially favored non-native species.

The authors posit that as older non-native trees die and native trees mature, the carbon stocks in these restored forests will increasingly transition to native species, potentially surpassing current values. The study highlights that while the specific diversity-AGB overyielding relationship was not detected in this restored TDEF (possibly due to the dominance of specific non-native species or the restored nature of the forest), the restoration of TDEFs offers a viable pathway to balance carbon sequestration goals with biodiversity conservation, soil erosion control, and water provisioning. The findings support a migration from species-poor, non-native plantations toward natural, high-diversity ecosystems for climate change mitigation and adaptation.

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