Biodiversity matters: rare species play an essential role in ecosystem multifunctionality

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Bouhedma National Park in Tunisia, one of the 123 sites sampled across the world
Bouhedma National Park in Tunisia, one of the 123 sites sampled across the world for this study © Yoann Pinguet

An international research team that included INRA and CNRS scientists has revealed the key role played by rare plant species in maintaining ecosystem "multifunctionality": both species and evolutionary diversity is important. This work was recently been published in PNAS . Based on data from 123 sampling sites around the world, the results show that taxonomic, functional, and phylogenetic biodiversity matters for ecosystem functioning. The findings also underscore that it is essential to protect rare species to ensure the proper functioning of ecosystems.

Ecosystems furnish multiple functions at the same time, an attribute that is referred to as multifunctionality. Such functions may include the transformation, recycling, or storage of nutrients and/or organic matter. Maintaining ecosystem multifunctionality is a significant environmental, economic, and societal challenge given global climate change and the biodiversity crisis.

It is important to consider more than just the number of plant species in an ecosystem. We must also account for the functional role of these species as expressed by their morphology, physiology, and phylogenetic history (i.e., their evolutionary relationships with other species). Because they produce large amounts of biomass, the most abundant species’the dominant species’play a major role in ecosystem dynamics. However, many species that are less abundant or even rare may also make a significant contribution, notably to ecosystem multifunctionality.

An international research team composed of scientists from INRA, CNRS, and Spanish research institutes studied the influence of plant biodiversity on the multifunctionality of terrestrial ecosystems. Using a standardised approach, the team examined biodiversity patterns at 123 sampling sites scattered across all the world’s continents (with the exception of Antarctica). They looked at very different ecosystems with contrasting plant assemblages, geological histories, and climatic conditions. These ecosystems included the African savanna, the desert steppes in China, the pampas of South America, the forests of Australia, the scrublands of the Mediterranean Basin, and the steppes of North Africa. The researchers then examined the relationship between the different biodiversity components (i.e., morphology, physiology, and phylogenetics) and multifunctionality by measuring 15 major ecosystem functions, including the transformation of nitrogen, phosphorus, and soil organic matter. As a result, they evaluated indicators of soil fertility, soil water retention, and biological productivity.

They found that the importance of biodiversity was about more than just plant species number. The results showed that, to maintain a high level of multifunctionality in terrestrial ecosystems, it was crucial to have rare species and, more specifically, rare species representing diverse phylogenetic lineages. In contrast, dominant species had a minimal effect on ecosystem multifunctionality, even if they made a major contribution to certain specific ecosystem functions, such as biomass production.

These findings highlight that it is important to protect rare species. We must move beyond the aim of preserving certain threatened species, which is the focus of conservation biology, and instead act with the broader objective of maintaining proper ecosystem functioning. Dealing with the current biodiversity crisis is therefore critical if we wish to maintain ecosystem multifunctionality and ecosystem services that are essential to humanity, such as food production, soil carbon storage, soil fertility, the production of potable water, and prevention of soil erosion.