Distinct diversity Trajectories of Boreal wood-inhabiting fungi following fire vs. clear-cutting

Here, we describe the data and methods supporting a study on how disturbances such as forest fires and clear-cutting influence wood-inhabiting fungal diversity trajectories in boreal Scots pine (Pinus sylvestris) forests in Northern Sweden. The research contrasts two chronosequences, one under rotational management (clear-cutting, soil scarification, and thinning) and one unmanaged and fire-origin.

Two contrasting disturbance regimes – wildfire and clear-cutting – are common in boreal forests, and create fundamentally different conditions for succession of wood-inhabiting fungi. We investigated (i) how species richness and community composition change after these two disturbances, and (ii) which stand-level characteristics drive diversity trajectories.

In two chronosequences – managed clear-cut (1–109yr since clear-cut; n=18) and unmanaged fire (4–375yr since fire; n=18) – we combined fruiting-body surveys with DNA metabarcoding to quantify species richness of wood-inhabiting fungi, including total number of species, Agaricomycete and red-listed species. To identify drivers, we measured deadwood attributes and forest structural complexity using terrestrial laser scanning.

Species richness, including red-listed species, was highest in unmanaged fire stands. Unmanaged fire stands had ~55 more total species than managed clear-cut stands at comparable time since disturbance (≤109yr), and ~156 more species in stands >109yr. Communities differed markedly between chronosequence types. Managed clear-cut stands harbored a subset of species found in unmanaged fire stands, and nearly all red-listed and indicator species were exclusive to unmanaged fire stands. Total and Agaricomycete species richness increased with time in both chronosequences without saturating. Red-listed species richness remained low and did not increase with time in managed clear-cut stands, but was higher and increased with time in unmanaged fire stands. Conditional random forest models identified spruce deadwood percentage, deadwood volume, and forest structural complexity as dominant diversity drivers, with deadwood quality replacing forest structure as the best predictor for red-listed species. Species richness rose steadily with deadwood volume, leveling at ~50m³ha⁻¹ for total species and >100m³ha⁻¹ for red-listed species.

Synthesis: Clear-cutting altered fungal recovery trajectories differently from fire. While fires leave standing and fallen dead trees that host fungal communities for centuries, clear-cutting removes these legacies and simplifies forest structure, resulting in a lack of recovery of red-listed species. These contrasting disturbance pathways shape boreal fungal communities through their effects on deadwood and structural continuity. Retaining high deadwood volumes and structural complexity can help maintain fungal diversity in managed forests, however maintaining old-growth stands is essential for conserving highly diverse communities and red-listed species.