Tree Neighborhood Diversity Boosts Growth—But Only in Wetter Climates

Redacción HC
11/09/2025

Biodiversity is often described as the foundation of healthy, resilient forests. Yet ecologists have long debated whether the diversity of a tree’s immediate neighbors can influence how well it grows, and how much this effect depends on climate. A new study published in Nature Ecology & Evolution (Zheng et al., 2025) provides one of the clearest answers to date: neighborhood diversity enhances tree growth, but the benefits are strongly tied to wetter climates—not simply to wetter years.

Why Neighborhood Matters in Forest Ecology

For decades, forest experiments have shown that mixed-species stands tend to outperform monocultures in overall productivity. However, much of that evidence has been gathered at the plot or stand level, not at the scale of the individual tree. The new study tackled a pressing question in restoration ecology:

"Does the diversity of neighbors immediately surrounding a tree enhance its growth, and does this effect vary depending on climate—both across wet and dry regions and during wetter-than-average years?"

This question is particularly relevant as climate change reshapes rainfall patterns worldwide, raising new challenges for forestry and restoration efforts.

A Global Dataset of Tree Diversity Experiments

To address this gap, the research team compiled an unprecedented dataset from 15 tree diversity experiments spanning four biomes. Altogether, the study encompassed:

• 852,170 growth measurements
• 113,701 individual trees
• 129 species

Neighborhoods were defined as a focal tree and its closest neighbors. The team measured both taxonomic diversity (species richness) and functional diversity (differences in traits). Climatic context was characterized using long-term precipitation averages as well as annual rainfall variability.

The analysis relied on hierarchical statistical models, controlling for species-specific and individual effects. This allowed the researchers to test whether neighborhood diversity consistently promoted growth and whether climate modified that relationship.

Key Findings: Climate Sets the Stage

The results were striking:

• Neighborhood diversity increased individual tree growth by 7–13% on average.
• The positive effect was strongest in sites with wetter climates, where water availability allowed species complementarity to flourish.
• Importantly, years with higher rainfall within a given site did not amplify the diversity effect. In other words, the benefit depends more on the long-term climate of a site than on short-term fluctuations in precipitation.

This nuance refines a well-known ecological principle: while diversity often leads to more efficient resource use and reduced pest pressure, the strength of these mechanisms depends on background conditions. As the authors note, “the gains from diversity are contingent on climate—particularly on water availability as a limiting resource” (Zheng et al., 2025).

What This Means for Forest Management and Restoration

The practical implications are clear:

• In humid regions, managers should prioritize species-rich, functionally diverse plantings to maximize growth, productivity, and carbon sequestration.
• In drier regions, while diversity still offers benefits, gains are more limited. Complementary interventions—such as water management, soil conservation, or shading strategies—may be needed to ensure success.
• Restoration programs should move beyond “tree counts” and consider neighborhood-level diversity as a critical factor in long-term forest health.

For policymakers, the study supports climate-smart reforestation strategies that adapt to local hydrological conditions. This is especially relevant for large-scale initiatives in the Amazon, Andean cloud forests, and temperate zones of South America.

Beyond Growth: The Bigger Picture

While this study focused on individual tree growth, the authors emphasize the need to explore broader ecosystem functions. Future research should investigate how neighborhood diversity shapes resilience to pests, carbon storage stability, and long-term forest dynamics as trees mature.

By integrating biodiversity into restoration planning, managers can foster ecosystems that are not only more productive but also more resilient in the face of climate uncertainty.

Conclusion: Designing Climate-Smart, Diverse Forests

The evidence from Zheng and colleagues underscores a powerful but context-dependent truth: biodiversity works best when the climate allows it to. For restoration projects, this means planting diverse mixes in wetter regions where gains will be greatest, while tailoring strategies in dry regions to mitigate water stress.

The future of reforestation lies in smart diversity—matching ecological principles with climatic realities to build forests that thrive in a changing world.

Topics of interest

Biodiversity