Study published in Nature reveals the hidden impact of human activity on biodiversity

An international study involving Ruben Heleno and José Miguel Costa from the Faculty of Sciences and Technology at the University of Coimbra (FCTUC) has concluded that natural vegetation often lacks species that should be present, particularly in areas heavily impacted by human activity. The research, led by the University of Tartu (Estonia), has just been published in the prestigious journal Nature.

More than 200 scientists from the DarkDivNet research network studied plant biodiversity at nearly 5,500 sites in 119 regions worldwide. At each site, they recorded all plant species and identified what is known as 'dark diversity' - the absence of native species. This approach allowed the researchers to assess the full biodiversity potential of the site and measure the degree to which this potential is realised, revealing the hidden impact of human activities on natural vegetation.

In regions with minimal human impact, ecosystems typically retain more than one-third of their potentially suitable species, with other species absent mainly due to natural factors such as limited seed dispersal. By contrast, in areas heavily affected by human activity, ecosystems contain only one in five suitable species. Traditional biodiversity measurements, such as simple species counts, fail to detect this impact because natural biodiversity variation across regions and ecosystems masks the true extent of human influence.

In Portugal, the team from the Centre for Functional Ecology (CFE) of FCTUC studied 34 sites in central Portugal, mostly forest fragments with varying degrees of disturbance, ranging from well-preserved areas to abandoned agricultural fields. The recorded species and their associations were then used to identify missing species in a site north of Coimbra, where the research group has been conducting studies for over a decade.

As in Coimbra, none of the 119 regions included in the study yielded significant conclusions when analysed in isolation. However, when all the data were combined, the researchers found that the proportion of 'missing' species was significantly higher in areas with a greater human presence - even when these sites had all the necessary characteristics to support natural vegetation.

The degree of human disturbance in each region was measured using the Human Footprint Index, which considers factors such as population density, changes in land use (such as urban development and agriculture), and infrastructure (e.g. roads and railways). The study concluded that local plant diversity is negatively affected by this index and most of its components, even at distances of several hundred kilometres.

"This is a worrying finding. On the one hand, it shows that the effects of human activities - such as roads, deforestation and pollution - extend far beyond areas traditionally considered disturbed. On the other hand, it shows for the first time that plants are struggling to recolonise areas that should be perfectly suitable for them. This is a warning sign of the crucial role of wild animals, especially in seed dispersal, a mechanism that seems to be compromised due to the decline of many animal populations," warns Ruben Heleno, professor in the Department of Life Sciences and researcher at CFE and the TERRA Associate Laboratory.

The study highlights the importance of maintaining and improving ecosystem health—not just within protected areas but beyond them as well. Additionally, dark diversity provides a practical tool for identifying species that should be present in a given location, thus helping to monitor the progress of ecosystem restoration.

The scientific article Global impoverishment of natural vegetation revealed by dark diversity is available here.