Quantifying the Impacts of Defaunation on Natural Forest Regeneration in a Global Meta-Analysis

Background

Intact forests provide critical ecosystem services like carbon storage and climate regulation, relying heavily on interactions between woody vegetation and animal species. However, defaunation alters these interactions on a global scale. While previous studies explore defaunation’s effects on individual ecosystems, no comprehensive global analysis quantifies its impact on natural forest regeneration. This study conducts a meta-analysis to assess how vertebrate loss influences forest regeneration across multiple regions and ecosystems, identifying key taxonomic groups and ecological processes most affected by defaunation.

Goals and Methods

The researchers systematically review and analyze data from 43 studies covering 41 forest landscapes in 27 countries. They compare forests with different levels of vertebrate abundance and assess defaunation’s effects on forest regeneration by examining changes in tree recruitment, seed dispersal, seed predation, and overall biomass accumulation. The authors categorize the impact based on which animals (e.g., primates, birds, ungulates) disappear and which ecological processes (e.g., seed dispersal, herbivory) get disrupted.

Conclusion

The meta-analysis shows that defaunation significantly reduces forest regeneration in real-world contexts, mainly due to the loss of seed dispersers such as primates and large birds. Vertebrate loss leads to declines in tree recruitment and shifts species composition, replacing large-seeded, high-carbon trees with smaller-seeded or abiotically dispersed species. Manipulated experiments that exclude specific animal groups produce mixed results—removing herbivores sometimes increases seedling survival—but the overall effect of defaunation remains negative for long-term forest health.