In a massive global study, researchers found that human activity significantly reduces plant diversity even in areas that appear relatively untouched. The findings challenge assumptions about how biodiversity is measured and suggest that the true scale of human impact on ecosystems has been underestimated.
Traditionally, biodiversity assessments have focused on counting the number of species present in a given area. But this approach misses a crucial piece of the puzzle that the species that should be there, based on ecological suitability, but aren’t. This concept, known as “dark diversity,” refers to the pool of plant species that are ecologically capable of existing in a habitat but are currently absent from it.
To explore this, scientists from nearly 30 countries surveyed more than 5,000 sites across 119 regions, analyzing both present and potential plant diversity. They discovered that in areas with little human interference, around 35% of the suitable species were present on average. However, in highly impacted regions, that number dropped to under 20%.
“We show that local plant diversity is globally negatively related to the level of anthropogenic activity in the surrounding region,” the authors wrote in the research paper. “Impoverishment of natural vegetation was evident only when we considered community completeness: the proportion of all suitable species in the region that are present at a site.”
“Pollution, deforestation, overgrazing and forest fires can exclude plant species from their natural habitats, preventing them from recolonising,” the authors wrote. “Human disturbance exerts a much greater impact than initially thought, even reaching protected areas far from the source of human impact.”
The work was part of the DarkDivNet project, launched in 2018 to systematically map dark diversity across the globe. In Spain’s Gorbeia Nature Reserve, researchers spent five years surveying beech forests and moors, navigating both pandemic-related restrictions and political instability in participating countries.
One key implication of the research is that restoration efforts could be more effective if they accounted for dark diversity. Many of the missing species still exist in nearby regions, and under the right conditions, could be reintroduced to their former habitats.
“Species in the dark diversity remain regionally present, and their local populations might be restored through measures that improve connectivity between natural vegetation fragments and reduce threats to population persistence,” the authors explained in the paper.
The study also supports a growing global conservation goal: protecting at least 30% of Earth’s surface. Researchers noted that regions with at least one-third of their area well preserved showed less negative impact from human activity, hinting at a buffer effect.
While more work is needed to translate these findings into specific conservation actions, the study offers a more nuanced and sobering view of biodiversity loss. It underscores the importance of not just preserving visible ecosystems, but also considering the invisible gaps in their ecological makeup.
This study was published in the journal Nature
