Temperate forest plants are associated with heterogeneous semi-open canopy conditions shaped by large herbivores

Abstract

Temperate forest plant diversity is declining despite increasing conservation efforts. The closed forest paradigm, emphasizing dense, continuous canopy cover, dominates current forest management strategies. However, this approach may overlook the historical role of large herbivores in maintaining semi-open forest conditions. Here we analyse the light and herbivory preferences of 917 native temperate forest plant species across central and western Europe, comparing these preferences with light availability in untouched closed-canopy forests and pasture woodlands. Plant species are 0.1–10 Myr old, with phylogenetic conservatism in habitat affinities (niche optima); thus, their distribution reflects long-term environmental states. We found that most temperate forest plants favour heterogeneous, semi-open-canopy conditions associated with high large-herbivore impacts, rather than uniform closed-canopy environments. On the basis of Red List criteria, high-affinity forest plants associated with higher herbivory and lower herbaceous biomass face higher extinction risk, indicating that low large-herbivore densities drive extinctions in present-day forests. These results align with palaeoecological evidence and high biodiversity in modern open woodlands, suggesting that closed-canopy dominance is a recent consequence of human-driven herbivore loss. Recognizing the role of large herbivores in maintaining semi-open vegetation offers new insights for biodiversity conservation and challenges the suitability of closed-canopy models in forest management.