A study recently published in Nature indicates that human activities have a negative effect on the biodiversity of wildlife hundreds of kilometres away. A research collaboration led by the University of Tartu assessed the health of ecosystems worldwide, considering both the number of plant species found and the dark diversity – the missing ecologically suitable species.
For the study, over 200 researchers studied plants at nearly 5,500 sites in 119 regions worldwide, including all continents. At each site, they recorded all plant species on 100 m2 and identified the dark diversity – native species that could live there but were absent. About 300 km2 surrounding each site was considered the region affecting the site. This allowed researchers to understand the full potential of plant diversity at each site and measure how much of the potential diversity was actually present.
High human impact wipes out four of five species
The study revealed that in regions with little human impact, such as in the vast forest masses of North America or in Greenland's tundra, ecosystems typically contain over a third of potentially suitable species, with other species remaining absent mainly due to natural reasons, such as habitats being too far apart or the lack of seed dispersers. By contrast, in forests of western and southern Europe and other regions heavily impacted by human activities, the sites studied contained only one out of five suitable species. Traditional biodiversity measurements, like simply counting the number of recorded species, did not detect this impact because natural variation in biodiversity across regions and ecosystems hid the true extent of human impact.
The level of human disturbance in each region was measured using the human footprint index. The index includes factors like human population density, land-use changes (i.e. urban development and conversion of natural to arable land), and infrastructure (roads and railways). The study found that plant diversity at a site is negatively influenced by human impact up to hundreds of kilometres away.
According to the lead author of the study, Professor of Botany of the University of Tartu Meelis Pärtel, the findings indicate that biodiversity can also be reduced in ecosystems that have not been directly modified by humans but are located in areas where human activities have caused habitat fragmentation or have had a dispersed impact on natural areas, for example through pollution.
"This result is alarming because it shows that human disturbances have a much wider impact than previously thought, even reaching nature reserves. Pollution, logging, littering, trampling and human-caused fires can trigger local extinctions and prevent recolonisation," explained Pärtel.
Evidence-based nature conservation targets
Researchers found that the negative influence of human activity was less pronounced when at least 30% of the surrounding region remained relatively pristine. According to Pärtel, this supports the global nature conservation targets to protect about one third of the land.
The study highlights the importance of maintaining and improving ecosystem health beyond nature reserves. The concept of dark diversity provides a practical tool for conservationists to identify absent suitable species and track progress in restoring ecosystems.
The study was conducted thanks to the international research network DarkDivNet , which started in 2018. The network is led by the University of Tartu, and its partners include researchers from nearly two hundred research institutions in 37 countries.
