Forests in Decline: New Global Evidence of Shrinking Resilience Under Climate Change

Redacción HC
17/11/2023

As the climate crisis accelerates, forests—long seen as one of humanity’s most powerful allies in absorbing carbon—may be reaching a dangerous tipping point. New research published in Nature provides the first global-scale evidence that the resilience of forests—their ability to recover from disturbances—is declining in tropical, temperate, and arid regions due to rising temperatures, reduced water availability, and increasing climate variability.

Based on satellite data and machine learning models, the study reveals a silent but alarming trend: even as many forests appear greener and more productive, their underlying capacity to withstand stress is weakening. If current patterns continue, vast forested regions could face abrupt shifts, releasing billions of tons of carbon into the atmosphere.

The Research Question: Are Forests Losing Resilience?

Forests cover about 30% of Earth’s land area and absorb nearly a third of human-induced CO₂ emissions. Their ability to perform this crucial role hinges on resilience—the capacity to recover from shocks like drought, fire, and disease.

Until now, while isolated studies have documented forest dieback, a global assessment of resilience trends was lacking. The research team, led by Giovanni Forzieri at the European Commission's Joint Research Centre, sought to answer a critical question:

Has global forest resilience declined from 2000 to 2020, and what climate factors are driving this trend?

How the Study Was Conducted: Data, Indicators, and Models

To quantify resilience, the researchers applied a sophisticated analytical framework:

• Data Source: Satellite-derived vegetation indices (MODIS kNDVI) at ~5 km resolution, spanning 2000–2020.
• Key Indicator: Temporal autocorrelation (TAC)—a mathematical signal of "critical slowing down," or declining recovery speed from disturbances.
• Trend Analysis: TAC trends were assessed in 3-year moving windows, generating an annual rate of change (δTAC).
• Climate Drivers: A Random Forest model estimated relationships between TAC and variables like precipitation, temperature, evapotranspiration, and climatic variability.
• Risk Assessment: The team calculated the percentage of forests crossing a critical TAC threshold—indicating possible irreversible decline.

While the study uses robust data and machine learning methods, it does not include ground-level species data or ecological succession, which may limit ecological specificity.

Key Findings: A Planet-Wide Warning Signal

Declining Resilience Across Most Forests

Over 53% of global forested land shows increasing TAC values, a clear signal of declining resilience. The breakdown by biome:

• Tropical, temperate, and arid forests all show significant TAC increases (weakened resilience).
• Boreal forests, in contrast, show decreasing TAC (improved resilience), likely due to warming and CO₂ fertilization enhancing productivity in colder climates.

Carbon Storage at Risk

Approximately 30% of intact forests have already crossed a critical resilience threshold. About 23% are actively degrading, putting an estimated 3.32 petagrams (Pg) of carbon at risk—three times the carbon released by 10 years of deforestation in Brazil’s Amazon.

Paradox of Greening but Weakening

A striking insight: in 36% of forests, productivity has increased, yet resilience has declined. This suggests that CO₂-driven greening may mask underlying fragility—akin to a tree that grows rapidly but becomes brittle under stress.

“Forest growth is not always a sign of health. Without resilience, ecosystems can collapse suddenly, turning carbon sinks into carbon sources.” — Forzieri et al., 2022

Managed vs. Intact Forests

Managed forests were found to have lower average resilience than intact ones. However, both follow similar declining trends, indicating that climate stressors—not just human land use—are the dominant factor.

Why It Matters: Implications for Policy and Society

This research redefines how we view forest health and the role of trees in climate mitigation. Key takeaways:

For Climate Policy

• Carbon sink reliability is not guaranteed. Policymakers must move beyond simple CO₂ accounting and incorporate ecosystem resilience into climate strategies.
• Hotspots of risk identified in the study should inform prioritization for conservation, adaptation, and reforestation efforts.
• Programs like REDD+ must consider not only carbon stocks but the stability of those stocks under future climate scenarios.

For Global Society

The findings offer a cautionary tale: climate change may be silently eroding the planet’s green defenses. Trusting forests to indefinitely soak up CO₂ while global temperatures rise may be a false hope.

Author Recommendations

• Integrate “resilience thinking” into forest management.
• Enhance long-term satellite and ground monitoring, especially in tropical and arid zones.
• Promote adaptive forest management that increases biodiversity, structural complexity, and water efficiency.
• Recognize that CO₂ fertilization benefits are temporary, especially under intensifying drought conditions.

Latin America in the Picture: High Stakes for the Global South

The Amazon Basin—home to over half of Earth’s tropical rainforest—falls within the regions at greatest risk. In countries like Peru, Colombia, and Brazil, national climate adaptation plans and forest conservation strategies must incorporate these resilience warnings.

Further south, Chile and Argentina face recurring megadroughts. This research strengthens the case for investing in water-efficient reforestation and restoring native vegetation, especially in fire-prone areas.

Conclusion: Forests Are Not Invincible

The global decline in forest resilience is a silent alarm. While forests still absorb large amounts of carbon, their capacity to recover is weakening under pressure from heat and water stress. The consequences of inaction are not just ecological—they're economic, climatic, and existential.

Call to Action: Policymakers, researchers, and civil society must adopt a new paradigm—one that values forest stability as much as forest growth. Monitoring resilience must become central to climate solutions.

Topics of interest

 Biodiversity  Climate