Holocene plant diversity in Southern Sweden: climate, fire, land-use synergy and forest conservation

High-resolution pollen and charcoal records from two bogs—Stavsåkra in the hemiboreal zone and Storasjö in the boreal zone of central Småland, southern Sweden—were used to reconstruct Holocene plant diversity and to disentangle the relative impacts of climate, fire, and anthropogenic disturbance. Four diversity metrics (richness, evenness, Simpson index, and Shannon–Wiener index) were applied to reconstruct plant diversity. Richness declined from 11 to 9.2 ka BP, remained low and variable between 7 and 3 ka BP, and increased again after 3 ka BP. These long-term trends track regional climate change. Superimposed centennial-scale variability was early Holocene, which maintained open canopies and high biodiversity. On the contrary, low fire frequency at Storasjö promoted closed conifer forests and lower diversity. The mid-Holocene low-fire regime at Stavsåkra decreased evenness, whereas moderate fire disturbance at Storasjö sustained mixed forests. After 1 ka BP, anthropogenic fires initially enhanced diversity, but ultimately reduced it when burning became excessive. The results corroborate the Intermediate Disturbance Hypothesis: moderate fire frequency maximises plant diversity, whereas both low-fire regime and high-frequency burning depress it. We therefore recommend integrating scientifically monitored prescribed burning into future forest management to restore disturbance regimes and conserve biodiversity in the boreal-hemiboreal landscapes.