Urban brownfields and their potential for nature conservation: what citizen science tells us?

Urban areas are increasingly recognized for their potential to support biodiversity, particularly through sites such as parks, gardens, and brownfields. Despite their conservation value, brownfields consisting of former industrial sites are frequently overlooked or redeveloped, risking biodiversity loss. Citizen science offers a unique opportunity to document the conservation value of these sites, providing data where traditional scientific surveys may be limited or absent. This study aims at evaluating conservation value of brownfields in a post-industrial region. We found that users predominantly record observations in quarries and coal mine sites, while heavily industrialized areas tend to be overlooked or underrepresented. We also found that brownfields, especially former coal sites and quarries, support high densities of protected species. However, they also harbour significant numbers of invasive species. In contrast, residential and agricultural areas show lower conservation potential due to intensive human activities. Although the uneven sampling effort across brownfields limits the reliability of ecological assessments and prevents a consistent evaluation of their potential value across all areas, our results indicate that, where data are available, brownfields can play an important role in supporting biodiversity in urban areas.