As forests reclaim the land: Latitudinal variations in carbon-biodiversity trade-offs under natural forest expansion in Italy

When agricultural land is abandoned, forests often regrow naturally. This process, called natural reforestation, is increasingly common in Europe and can help store carbon (C), which is important for slowing climate change. At the same time, it may affect biodiversity, especially plant species that thrive in open landscapes.

This study examined 16 chronosequences across Italy, representing different stages of land recovery over about 75 years, from grasslands to mature forests. The sites were spread across Alpine, Continental, and Mediterranean regions. Researchers measured carbon stored in vegetation, deadwood, and soil, and also assessed the diversity of herbaceous (non-woody) plants.

The results showed that total ecosystem carbon increased steadily as forests developed. This was mainly due to the growth of trees, which become the dominant carbon storage over time. In contrast, soil carbon did not show a clear pattern and varied depending on local conditions.

Plant diversity followed a different trend. Herbaceous species richness was highest in open habitats such as meadows and pastures, or in the early stages of forest regrowth. As forests became denser and tree canopies closed, light availability decreased, leading to a decline in these plant species in most sites. This created a clear trade-off: areas with higher carbon storage tended to have lower herbaceous plant diversity.

However, this pattern was not the same everywhere. In the southernmost site (Basilicata), plant diversity showed a U-shaped trend: it decreased at first but partially recovered in later stages of forest development. This suggests that under certain environmental conditions, both carbon storage and biodiversity can improve together, although diversity may not fully return to its original levels.

Overall, the study highlights that natural forest expansion is beneficial for carbon sequestration but can reduce plant diversity, especially in the short to medium term. These trade-offs are important for land management and environmental policy. In some cases, however, they may decrease over time, offering opportunities to balance climate and biodiversity goals.