To stand or not to stand - How tree death impacts fungal community development in spruce logs

Complementary to windthrows, trees often die following gradual decline and may remain standing dead for years. This natural process is suppressed by timber harvesting, fire-risk management, pest control, and safety interventions, even in protected areas. Such practices prevent the formation of standing deadwood and remove existing snags, potentially threatening specialised deadwood-dependent organisms. Yet the influence of tree mortality mode on fungal communities remains poorly understood. We studied fungal communities on 59 Norway spruce trees representing three dead wood types representing two mortality modes: (a) uprooted trees that fell while alive, (b) fallen trees that had remained standing dead for years to decades before falling, and (c) still standing dead trees. Sampling combined sporocarp surveys with eDNA metabarcoding in a primeval forest area in Czechia. Fungal communities differed significantly among mortality modes, with trees with a time gap between death and falling maintaining distinct communities even after decades of decay. Mortality mode a significant factor for community composition, although not as strong as decay stage. Dry-standing trees after their fall host more total and red-listed species than windthrows. Our findings highlight the importance of retaining diversity of natural mortality modes as crucial for forest management and conservation, and that tree species and decay stage alone are insufficient to maintain fungal diversity. Preserving both standing snags and naturally uprooted trees is essential to sustain fungal diversity. Management practices that simplify or homogenise deadwood formation risk losing specialised species, emphasising the need for targeted deadwood management even in managed forests. • Downed snags retain distinct fungal communities even in late decay. • Sporocarp surveys and ITS2 eDNA reveal complementary community patterns. • Conserving diverse mortality pathways may support rare saproxylic fungi.