Geographical gradient of fungal decay type in Norway spruce logs in Europe and its impact on seedling establishment

Norway spruce (Picea abies) is a dominant tree species across Eurasia.
Understanding its regeneration dynamics is crucial for predicting forest
sustainability under climate change. In certain types of Norway spruce
forests, regenerates is more successful on decaying logs and stumps than
on the forest floor. The type of wood decay, indicative of fungal decay
capabilities, markedly influences spruce regeneration, demography, and
growth. As fungal distribution and wood decay types are affected by
macroclimate, the success of spruce seedling regeneration is expected to
vary continentally and may be further influenced by climate change. The
present study examined decay type frequencies and seedling densities on
decaying Norway spruce logs, assessing effects on regeneration success
across 15 sites in 6 European countries along a latitudinal gradient.
White rot was dominating in central Europe compared with southern and
northern Europe. Spruce seedling densities were positively correlated with
white rot in heartwood, particularly influenced by high precipitation
seasonality in central Europe. These findings suggest that spruce seedling
regeneration on decaying logs may be indirectly affected by climate
through its influence on fungal-mediated wood decomposition. Despite
predictions of northward shifts in Norway spruce distribution due to
climate change, slower regeneration rates on brown rot logs may limit
northern expansion, potentially leading to a contraction of the species’
range.