Natural ecosystems comprise groups of species capable of living in the specific conditions of a biological system. However, if we visit a specific natural area, we will not find all the species capable of living in it. The proportion of species that could live in a specific location but do not do so is known as dark diversity, a concept coined in 2011 by researchers at the University of Tartu (Estonia). Research involving the UPV/EHU has now discovered that this dark diversity increases in regions with greater human activity. The study was recently published in Nature, one of the world's most influential journals.

The study, in which the Biodiversity and Evolution Research Group of the UPV/EHU’s Faculty of Science and Technology participated, was carried out within the framework of the international DarkDivNet network and focused on nearly 5,500 locations in 119 regions across the world. In each location studied, the research teams analysed all the plant species present in different habitats to identify dark diversity. This innovative methodology for studying biodiversity made it possible to estimate the potential plant diversity in each study site and compare it with the plants actually present.

The results reveal a hitherto unknown effect of human activities on biodiversity. In regions with little human impact, natural habitats contain on average one third of the potential species, mainly because not all the species can spread throughout the area naturally. By contrast, in regions with a high human impact, habitats tend to include only one fifth of the potential species. Traditional methods for estimating biodiversity, based on counting the number of species present without taking potential species into consideration, tend to underestimate the true effect of human impact.

The Gorbeia Nature Reserve

Based on the original idea of Professor Meelis Pärtel of the University of Tartu and lead author of the study, the DarkDivNet network was launched in 2018. Since then, research groups from all over the world have been gradually joining in order to gather samples in as many regions of the planet as possible. A case in point was the UPV/EHU’s scientific team formed by Idoia Biurrun-Galarraga and Juan Antonio Campos-Prieto, lecturers in the Botany section of the Department of Plant Biology and Ecology; they chose the Gorbeia Nature Reserve as the setting for sampling 55 study sites, targeting beech forests and moors as habitats. The work took five years to complete and had to contend with the COVID-19 pandemic and political crises in many countries within the network.

The degree of human impact in each region was measured using the Human Footprint Index, based on factors such as population density, changes in land use and infrastructure construction (roads). The study showed that the human footprint index negatively affects plant diversity in a locality within a radius of several hundred kilometres. The authors pointed out that the results “are alarming because they show that human disturbance exerts a much greater impact than initially thought, even reaching protected areas far from the source of human impact. Pollution, deforestation, overgrazing and forest fires can exclude plant species from their natural habitats, preventing them from recolonising”. The researchers also pointed out that “the negative influence of human activity was less pronounced when at least one third of a region's area remained well preserved, which supports the global goal of protecting 30% of the planet's surface”.

In conclusion, this study highlights the importance of maintaining healthy ecosystems beyond nature reserves and emphasises the concept of dark diversity as a useful tool for assessing the status of ecosystems undergoing restoration, identifying species that have a preference for a particular habitat but are not yet present in it.

Reference

Pärtel, M., R. Tamme, C. P. Carmona, K. Riibak, M. Moora, … I. Biurrun, … J.A. Campos,… and M. Zobel (2025) "Global impoverishment of natural vegetation revealed by dark diversity." Nature. DOI: https://www.nature.com/articles/s41586-025-08814-5