Clonal Beech Forests Create Refuges for Rare Mountain Plants

What is it about?

This study examined a rare, unmanaged beech forest (Fagus sylvatica) in the Pollino Massif of southern Italy, located at the highest elevation where beech naturally occurs in the Mediterranean region (up to 2,140 m above sea level). The researchers wanted to understand how the forest structure changes with elevation and how those changes affect vascular plant biodiversity beneath the trees.

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Why is it important?

Most Mediterranean beech forests have been heavily influenced by centuries of logging and coppicing. As a result, little is known about what beech forests looked like before human disturbance, especially at very high elevations. This forest is one of the few remaining natural relic stands and is in a glacial refuge, an area where species survived past ice ages. What did the researchers find? As elevation increased, the appearance and growth form of beech trees changed dramatically. Below about 2,000 m, trees were mostly tall, upright, and single-stemmed. Above 2,000 m, trees became shorter, bent, and multi-stemmed. Many high-elevation trees reproduced clonally through layering, where low branches touch the ground, develop roots, and form new stems genetically identical to the parent tree. This created dense clusters of interconnected stems known as clonal stands. Stem density increased enormously with elevation, while individual tree size decreased. Near the upper limit of the forest, tens of thousands of stems per hectare were recorded. Why does this happen? The authors concluded that harsh mountain conditions, especially: heavy and persistent snow cover, strong winds, steep slopes, and low temperatures, make it difficult for trees to grow tall and upright. Instead, beech trees survive by spreading horizontally and reproducing clonally. This growth form helps them withstand snow pressure and maintain forest cover in a challenging environment. How does this affect biodiversity? The dense, low canopy created by clonal beech trees produces a cooler and more stable microclimate close to the ground. This protected environment allows several rare, endemic, and cold-adapted plant species to survive, including species that are uncommon elsewhere in southern Italy. The study found that these special understory plants were strongly associated with the high-elevation clonal forests. The beech canopy acts as a natural refuge, buffering plants against climate extremes and helping them persist in the southernmost part of their range.

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