We are living amidst humanity’s largest ever migration with more people moving from rural areas to cities than ever before. Rural populations are predicted to plummet by over 50% in the next 50 years, leaving behind abandoned crop fields and entire settlements. Тhese abandoned lands might offer opportunities to restore ecosystems, and allow biodiversity to recover from other anthropogenic pressures. However, abandoned fields are often dominated by a small number of potentially invasive species, which could pose threat to species that have historically persisted alongside traditional, low-intensity farming. Here, we ask how ecosystem structure, habitat heterogeneity and biodiversity have changed after farming has ceased and human settlements have been depopulated. We focus on Bulgaria, a global hotspot of countryside abandonment. For over 5000 villages, we analyze in-situ ecological data, sociodemographic information and satellite imagery to quantify land cover and human population trajectories over time. For 30 of these villages along a gradient of abandonment, we compare biodiversity patterns using acoustic monitoring and ground surveys of bird and plant communities.
Results/Conclusions
We found that countryside abandonment is widespread in Bulgaria. Human populations in rural areas declined by 57% from 1934 to 2020, and over 200 villages have been entirely depopulated. Declines in human population were positively correlated with increases in abandoned land, particularly in mountainous regions. In contrast, in lowland regions abandonment and depopulation co-occurred more rarely. Human depopulation corresponded with country-wide increases in forests and shrublands and declines in grasslands. Higher rates of human depopulation were also linked with declines in land cover heterogeneity and increases in forest connectivity. At local scales, countryside abandonment altered bird and plant communities, particularly for grassland species. Across our study gradient, abandonment favored a similar subset of birds, whereas villages that were still inhabited had more diverse bird communities. Similarly, for plants, a subset of woody and grassy species became increasingly dominant as time since abandonment increased. Our findings highlight the ecological consequences of human migration and depopulation and suggest that land abandonment is a key driver of biodiversity change whose influence will only increase in the future in Bulgaria, and around the world.
