Natural vegetation often lacks many species that could potentially be present, especially in regions heavily affected by human activities, according to a new study coordinated by researchers at the University of Tartu and published in Nature. Researchers from Lund University, Stockholm University and the Swedish University of Agricultural Sciences (SLU) also participated in the study.
Over 200 scientists from the research collaboration DarkDivNet studied plants at nearly 5500 sites in 119 regions around the world. At each site, local researchers recorded all plant species and identified the dark diversity – native species that could live there but were absent. This allowed them to understand the full potential of plant diversity at each site and measure how much of the potential diversity was actually present. This way of measuring biodiversity revealed the hidden impact of human activities on natural vegetation.
Human impact stronger than expected
“We were surprised that large-scale human impact had such a strong effect on the local flora. The results show that conservation efforts cannot focus solely on isolated nature reserves – it is also essential to consider environmental conditions at a regional scale,” says Honor Prentice, Professor Emerita in Biology and BECC PI at Lund University was one of the Swedish researchers who participated in the study.
In regions with little human impact, ecosystems typically contain over a third of potentially suitable species, with other species remaining absent mainly due to natural reasons, such as limited dispersal. In contrast, ecosytems in regions heavily impacted by human activities, contain only one out of five suitable species. Traditional ways of inventorying biodiversity, such as simply recording the number of species, failed to reveal this effect of human activity, because natural variation in biodiversity across regions and ecosystems masks the true extent of human impact.
The DarkDivNet collaboration started in 2018, based on an idea by Professor Meelis Pärtel, lead author of the study.
“We had introduced the dark diversity theory and developed methods to study it, but to make global comparisons we needed consistent sampling in many regions. It felt like an impossible mission, but many colleagues from different continents joined us”, says Meelis Pärtel.
Negatively influence up to hundreds of kilometres away
The level of human disturbance in each region was measured using the Human Footprint Index, which includes factors like human population density, land-use changes (such as urban development and agriculture), and infrastructure (roads and railways). The study found that plant diversity at a site is negatively influenced by the level of the Human Footprint Index and most of its components in a surrounding area, up to hundreds of kilometres away.
“This result is alarming because it shows human disturbances have a much wider impact than previously thought, even reaching nature reserves. Pollution, logging, littering, trampling and human-caused fires can exclude plants from their habitats and prevent recolonization. We also found that the negative influence of human activity was less pronounced when at least one-third of the surrounding region remained pristine, supporting the global target to protect 30 percent of the land”, Professor Pärtel summarises.
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.
Link to the article in Nature:
Global impoverishment of natural vegetation revealed by dark diversity