Planting forests plays a crucial role in fighting climate change, safeguarding biodiversity, and supporting sustainable development goals when done correctly. Forests act as carbon sinks, trapping and storing atmospheric carbon. Yet planting too many trees without thoughtful planning can strain ecosystems. Recent research shows that forests with a mix of tree species excel at carbon capture because different species bring complementary traits that boost overall storage.
Compared with single-species stands, mixed forests tend to resist pests, diseases, and climate disturbances more effectively. This resilience supports higher long-term carbon storage. In addition, multispecies forests provide a wider range of ecosystem services, contributing to greater biodiversity and healthier landscapes.
Although the benefits of diverse forest systems are widely recognized, many restoration projects worldwide focus on monoculture plantations. An international team of scientists evaluated carbon reserves in forests with multiple tree species against those in monocultures. Their findings were published in Boundaries and Global Change in Forests.
In the study, forests with varied tree communities stored more carbon than monocultures, with increases exceeding 70 percent in some cases. The greatest gains in carbon storage relative to monocultures were observed in four-species mixtures, according to Emily Warner, a postdoctoral researcher in Ecology and Biodiversity Sciences at the University of Oxford, and the study’s lead author. Warner noted that diverse forests captured substantially more carbon than even high-yield monocultures.
Four species outperform six in carbon storage
The researchers examined studies published since 1975 that directly compared carbon storage in mixed forests and single-species stands. They also incorporated previously unpublished data from a global network of tree-diversity experiments to form a comprehensive view. The aim was clear: determine whether forest diversification delivers measurable carbon benefits.
Among the mixed forests analyzed, configurations incorporated two to six tree species. Results showed that four-species mixtures were the most effective at storing carbon. One of these optimal mixes included broadleaf trees commonly found across Europe.
Mixtures that included both high-density and complementary leaf types demonstrated greater carbon capture than monocultures and stored up to 35 percent more carbon. Surprisingly, six-species forests did not show a clear advantage over monocultures.
Up to 70 percent boost in efficiency
The evidence indicates that forest diversification enhances carbon storage. Total aboveground carbon stocks in mixed forests rose by about 70 percent compared with monocultures. In many cases, mixed forests achieved 77 percent higher carbon stocks than commercial monocultures, which often prioritize high-yield species. As global pressure to replant trees grows, these findings suggest mixed-species plantations can deliver substantial climate benefits in addition to other ecological gains.
Senior forest restoration scientist Susan Cook-Patton of Nature Conservation, a collaborator on the study, emphasized that diversification offers broader advantages beyond carbon storage and should be part of planning for new forests.
The results hold particular relevance for forest managers seeking productive futures for planted forests. The study highlights a potential productivity incentive for new planting strategies that incorporate species diversity while still meeting local needs and conditions.
While the evidence for higher carbon storage in mixed forests is strong, researchers caution about limitations. Comparisons between mixed forests and monocultures are fewer for older stands or those with very high tree diversity. Long-term data are needed to understand the mechanisms behind the observed effects and to explore how location, species choices, and forest age influence outcomes.
Warner remarked that the study demonstrates the promise of diversification in planted forests and calls for ongoing experimental work to explore the drivers behind these results. A broader understanding of how different settings affect carbon storage will help guide future restoration and afforestation efforts. We can expect more findings as researchers continue documenting how climate, soil, and management interact with species composition.
Reference work: DOI: 10.3389/ffgc.2023.1226514
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Note on data collection and coordination: A coordinated environmental research effort contributed to the global data set used in the analysis, underscoring the value of collaboration across institutions and regions to advance forest restoration science.