Fires beyond fire-prone ecosystems: the beech forest
Beech (Fagus sylvatica) forests occur in relatively cold, moist environments and, as shade‑tolerant, winter‑deciduous trees, their dense summer canopy suppresses understory vegetation and fires, often acting as flammability barriers. Thus, they can be considered non‑flammable. However, the large 2025 fires in Spain and Portugal that occurred during an exceptional heatwave [1] burned many different vegetation types, including beech forests, such as those in the Picos de Europa (León, northern Spain) [2]. This is a novel fire regime. Approximately one‑third of the beech forest was either unaffected (the flammability barrier was effective) or burned by a very low‑intensity understory fire, with 99% of trees surviving (very low severity). Another third burned in an understory fire that killed most trees (a low‑intensity, high‑severity fire). The remaining third comprised a mix of dead and surviving trees that did not fully recover their crowns (moderate severity).
Ten months postfire, seedling regeneration of beech was poor; in contrast, there was a large amount of seedling regeneration of native woody legumes (Cytisus, Genista). This suggests that a type‑conversion from non‑flammable forest to flammable shrubland is very likely.
Global warming weakens the flammability barrier and enables fire to spread beyond fire‑prone ecosystems, affecting fire‑sensitive species. In the Anthropocene, terms like ‘non‑flammable’ and ‘pyrophobic’ are becoming increasingly irrelevant!
References
[1] Sánchez-Hernández G, Turco M, Repeto-Deudero I, Royé D, Baudena M, Montávez JP, Pietroiusti R, Provenzale A, Santin C, Torres-Vázquez MA, Pausas JG. 2025. Record-breaking 2025 European wildfires season concentrated in the western Iberian Peninsula. Global Change Biology 31:e70649 [doi | pdf]
[2] Pausas JG, Valbuena L, Beltrán-Marcos D. 2026. Fires beyond fire-prone ecosystems: the erosion of beech forest. Global Change Biology 38: e71036 [doi | pdf]