Forest conservation and restoration are important tools to counter threats caused by habitat fragmentation and global change. But to promote forest diversification and resilience, we must first understand the dynamics of how plants respond to past climate change.

A study published in the Proceedings of the National Academy of Sciences (PNAS), coordinated by the Department of Environmental Biology at Sapienza University of Rome, analysing pollen and fossil spores from sediment samples from the bottom of Lake Ohrid, a large freshwater basin located on the border between Albania and North Macedonia, identifies and describes the response of numerous forest elements to climate change caused by glacial-interglacial oscillations over the last 1.36 million years.

The sediment record of Lake Ohrid represents the oldest continuous lake archive in Europe, from when the lake was generated.

This new research explains the importance of a wetland such as Lake Ohrid as a refuge for plants during the less favourable climatic phases, i.e. arid and cold.

The results suggest that around 1.16 million years ago, the area around Lake Ohrid was characterised by forests that gave way to a more open environment, with grasses and shrubs indicating increased dryness and deepening of the lake waters. This phase was followed by another transition, about 0.94 million years ago, due to the vegetation's response to longer and more pronounced glacial-interglacial cycles. Many plants, elsewhere extinct or rare, have had a greater persistence in the Ohrid area, showing that the lake was an area of refuge, at least until about 1 million years ago. The study also highlights how many trees had more or less rapid declines before disappearing.

"The evaluation of long-term effects concerning global climate and local vegetation change," says Alessia Masi of Sapienza University, "reveals a significant influence of wet interglacial conditions on subsequent plant composition and diversity during the glacial period."

"This effect," concludes Laura Sadori of Sapienza, study coordinator, "is opposite in observations at high latitudes, where glacial intensity is known to control subsequent interglacial vegetation, and the evidence shows that the Lake Ohrid basin functioned as a refuge for both thermophilic and temperate tree species."

According to the authors, the record of Lake Ohrid can make a significant contribution to forest management and research into their resilience to future climate change.

References:

1.36 million years of Mediterranean forest refugium dynamics in response to glacial-interglacial cycle strength - Timme Donders, Konstantinos Panagiotopoulos, Andreas Koutsodendris, Adele Bertini, Anna Maria Mercuri, Alessia Masi, Nathalie Combourieu-Nebout, Sébastien Joannin, Katerina Kouli, Ilias Kousis, Odile Peyron, Paola Torri, Assunta Florenzano, Alexander Francke, Bernd Wagner and Laura Sadori - PNAS 2021 DOI: https://doi.org/10.1073/pnas.2026111118

Further Information

Laura Sadori
Department of Environmental Biology
laura.sadori@uniroma1.it

Alessia Masi
Department of Environmental Biology
alessia.masi@uniroma1.it