Holocene Plant Diversity in Southern Sweden: Climate, Fire, Land-Use Synergy and Forest Conservation

Xiaolei Liu^1,2Qiaoyu Cui^1*Wenchao Zhang³Feng Qin¹Quan Li¹Yao Zhang⁴Geoffrey Lemdahl⁵Marie-José Gaillard^5*

• ¹Chinese Academy of Sciences Institute of Geographic Sciences and Natural Resources Research, Beijing, China
• ²University of the Chinese Academy of Sciences, Beijing, China
• ³China University of Geosciences Beijing School of Earth Sciences and Resources, Beijing, China
• ⁴Zhejiang Normal University, Jinhua, China
• ⁵Linneuniversitetet, Kalmar, Sweden

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 rose from 11 ka BP to a peak at ~9.5 ka BP; it declined between 7–3 ka BP; and then 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.