Species richness linked to forest productivity in the eastern U.S.

When scientists and policymakers decide on which regions to prioritize for conservation, biodiversity is frequently their top consideration. The rationale is clear: ecosystems with higher biodiversity tend to support a broader range of species and offer a wider spectrum of ecosystem services, making them prime candidates for conservation.

However, the task of quantifying biodiversity is fraught with challenges. Various metrics offer different lenses through which the intricate interactions of life within ecosystems, such as forests, can be viewed, sometimes leading to conflicting interpretations of biodiversity’s significance.

Measuring forest productivity 

A recent study led by the Florida Museum of Natural History has shed light on this issue through a detailed analysis of two decades’ worth of data. This comprehensive review suggests that the most straightforward biodiversity metric – simply counting the total number of species within a specific area – provides the most accurate reflection of a forest’s productivity.

“Ecosystem services provided by forests – including wildlife habitat, wood, fiber, and carbon storage – depend on forest productivity, the collective biomass growth of individual trees. Forest productivity is thought to increase with tree biodiversity, but there are many ways to quantify biodiversity, with little consensus on which measures are most important,” wrote the study authors.

“Despite experimental and observational studies demonstrating that biodiversity enhances primary productivity, the best metric for predicting productivity at broad geographic extents – functional trait diversity, phylogenetic diversity, or species richness – remains unknown.”

Biodiversity metrics and forest productivity 

“There aren’t many studies that look at the differences between measurements of diversity,” said lead author Yunpeng Liu, a postdoctoral associate at the Florida Museum. With access to an extensive database maintained by the U.S. Forest Service, 

Liu and his team set out to explore how different biodiversity metrics correlate with the productivity of forests across the eastern United States, drawing on nearly two million tree measurements from 23,145 forest plots collected between 2000 and 2020.

Forests with diverse species interactions 

The findings revealed a consistent trend: forests with a higher number of tree species, or species richness, demonstrated greater productivity. This aligns with the understanding that diverse species interactions within an ecosystem bolster essential services such as carbon sequestration and provide renewable resources like wood.

Contrary to initial expectations, the study found that measures of phylogenetic diversity (which tracks the evolutionary relationships among species) and functional diversity (which looks at the variety of structural and biological traits) were negatively correlated with productivity. This unexpected discovery complicates the narrative on how different dimensions of biodiversity influence ecosystem functionality.

However, as co-author Douglas Soltis (a distinguished professor with the Florida Museum of Natural History) argues: “These aren’t mutually exclusive measurements. They’re all ways that we might be able to make better conservation decisions.”

Ecosystem resilience and productivity 

The study also ventured into the implications of these findings for ecosystem resilience and productivity. Co-author Robert Guralnick, curator of biodiversity informatics at the Florida Museum, admitted the uncertainties that still linger, highlighting the ongoing need for research into the dynamics of tree interactions and the traits that enable diverse forests to flourish.

Unfortunately, there is not enough information about various specific traits, such as the shape and depth of roots, to make accurate assessments. “It may also be that there are aspects of how trees of the same or different species structure their interactions with each other, especially as tree communities become more diverse, that we don’t yet understand,” Guralnick added.

Valuable insights for conservation practices

By illuminating the multifaceted role of biodiversity in forest health and productivity, the study provides valuable insights for conservation practices. It particularly highlights the significance of species richness as a straightforward and reliable indicator for evaluating ecosystem health. 

“It’s reassuring for other investigators and policymakers to know that species richness is reliable. This is especially important when making conservation decisions with short notice and limited data,” Soltis concluded.

The study is published in the journal Proceedings of the National Academy of Sciences.

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