[Science News] – The Semois Valley reveals exceptional lichen biodiversity

As part of a mission commissioned by the Semois Valley National Park, Damien Ertz, a researcher at Meise Botanic Garden, conducted an in‑depth lichen inventory between 2024 and 2025. The study focused on 35 rocky outcrops located across the municipalities of Bertrix, Bouillon, Chiny, Florenville, Herbeumont and Vresse‑sur‑Semois. It aimed to assess the ecological richness of these habitats—often nestled within ancient forests—and the results confirm that the region is a major reservoir of biodiversity.

A total of 465 species were recorded, including 397 lichens, 59 lichenicolous fungi (living on lichens) and 9 “semi‑lichens”. To achieve such precision, a rigorous methodology was applied: detailed examination of 542 trees and analysis of 1,754 quadrats on rock faces. This meticulous approach led to the identification of 17 lichen species and 8 lichenicolous fungi previously unknown in Belgium.

The most remarkable discovery of the mission is undoubtedly a fungus species new to science: Talpapellis chlorinae. The inventory also brought to light macrolichens once thought to have disappeared from the national territory, such as Fuscopannaria mediterranea and several species of the genus Usnea. These findings highlight the unique heritage value of the schist cliffs and ravine maple forests of the valley.

Some sites proved exceptionally rich. Rocher Lecomte and Rocher Génifa stand out in particular, with such high diversity that a proposal has been made to designate them as nature reserves. Across the valley, twelve sites exceed the threshold of 120 lichen species, confirming the critical importance of rocky outcrops for the conservation of lichen flora at the national scale.

The study also underscores the role of well‑preserved ancient forests. The presence of species such as Biatora veteranorum, observed on deadwood, or the very rare Thelotrema suecicum, serves as a valuable indicator of the ecological continuity of these habitats. Though discreet, these organisms are direct witnesses to the health of the Semois Valley’s forest and rocky ecosystems.

This inventory demonstrates that the Semois Valley harbours a natural heritage that remains largely under‑documented. Preserving rocky outcrops and maintaining substantial volumes of deadwood in forests are essential to safeguarding this remarkable biodiversity.

> The full report is available on the National Park’s website.