Tropical Forest Comeback: How Secondary Growth Restores Ecological Functions

Redacción HC
21/09/2023

In the face of widespread deforestation across the Neotropics, secondary tropical forests—those regrowing naturally after land abandonment—are quietly becoming one of the most important allies in the fight against climate change and biodiversity loss. But a key question remains: Can these forests fully recover their ecological function, or are they forever diminished?

A groundbreaking study published in Proceedings of the National Academy of Sciences (PNAS) sheds new light on this issue. Drawing from more than 1,000 forest plots across 30 sites in Latin America, researchers found that secondary forests can regain crucial functional traits over time, challenging assumptions that only primary forests are ecologically valuable.

Nature’s Second Wind: The Role of Secondary Forests

Roughly a third of the Neotropical landscape is now covered by secondary forests—land that was once cleared for agriculture or pasture but has since been left to regenerate. These forests are more than a green backdrop; they provide carbon storage, water regulation, habitat for wildlife, and buffer communities against climate risks.

However, the extent to which they recover their functional diversity—the traits that determine how ecosystems work—has been unclear. This study sought to answer a crucial question:

How does the functional composition of tree communities evolve in secondary forests over time, and how does this vary between humid and dry climates?

A Data-Driven Approach to Measuring Forest Recovery

To investigate functional recovery, the researchers conducted a comparative analysis across 1,016 forest plots spanning successional ages from recent regrowth to forests more than 50 years old. They examined seven plant traits, including:

• Wood density
• Maximum tree height
• Leaf size and shape
• Drought and shade tolerance

These traits were analyzed to calculate three main ecological metrics:

• Community-weighted mean (how dominant certain traits are)
• Functional range (trait diversity)
• Successional trajectory (how these traits shift with age and climate)

This allowed scientists to track how ecological functions change as forests mature, particularly across humid vs. dry tropical regions.

Methodological Notes

The study used a chronosequence approach, comparing forests of different ages across locations to infer long-term trends. While efficient, this method can introduce limitations due to local variations in land use history and environmental conditions.

Key Findings: A Tale of Two Forest Types

1. Functional Convergence with Maturity

Regardless of climate type, secondary forests showed strong convergence with the functional profiles of mature forests after about 50 years. Key traits like wood density and stress tolerance became increasingly similar to those found in undisturbed forests.

“In forests older than 50 years, functional traits align closely with those of old-growth ecosystems,” the authors report.

2. Climate-Driven Trait Selection

• Dry forests initially favor drought-tolerant species, prioritizing survival under water stress.
• Humid forests support fast-growing, shade-tolerant species, accelerating biomass accumulation in early stages.

These findings emphasize the need for climate-sensitive restoration strategies, especially under shifting rainfall patterns driven by climate change.

3. Increasing Functional Diversity Over Time

As forests mature, their functional range broadens, reflecting the development of more complex and diverse ecological niches. This increase in trait variety indicates a more resilient and multifunctional forest system.

4. Implications for Carbon and Nutrient Cycling

• Young dry forests capture less carbon due to the dominance of small, drought-resistant trees with low wood density.
• Humid forests, by contrast, experience early boosts in carbon storage thanks to rapid-growing species with lighter wood.

This suggests that secondary forests in humid zones may offer faster returns for climate mitigation, while dry forests may need targeted interventions to boost carbon capture and resilience.

What This Means for Forest Policy and Climate Action

Passive Restoration Works—With Caveats

The study provides robust support for natural regeneration as a viable restoration strategy, particularly in humid tropical regions. Letting nature heal itself—when left undisturbed—can lead to substantial ecological recovery.

However, in dry ecosystems where recovery is slower and more variable, active interventions such as planting drought-resistant species may be necessary to kickstart the regeneration process.

Tailoring Strategies to Climate

The research reinforces a crucial principle: One-size-fits-all restoration does not work. Policies should account for local conditions and be grounded in ecological data—not just tree counts or carbon metrics.

Maximizing Carbon Sequestration

With functional traits linked to biomass and carbon cycling, secondary forests can be integrated into national climate strategies. Countries like Brazil, Colombia, and Costa Rica can harness these ecosystems as part of their climate commitments under the Paris Agreement.

Final Thoughts: Rethinking the Value of Second-Growth Forests

This study challenges the idea that only primary forests matter. It reveals that secondary forests—given time and the right conditions—can reclaim their ecological roles, from carbon storage to biodiversity support.

For conservationists, policymakers, and landowners, this is a powerful message:

Restoration is not just about planting trees—it’s about restoring function.

Topics of interest

Biodiversity Climate