Large-scale dieback of Norway spruce (Picea abies (L.) H.Karst.) in Central Europe has created extensive post-disturbance areas that are typically managed by salvage logging. While logging residues are often removed or concentrated in skid trails, retaining fine woody debris (FWD) may improve microsite conditions for tree regeneration by modifying microclimate and competing vegetation. This study investigates the effects of local FWD enrichment on microclimate and vegetation cover on Norway spruce calamity areas in the Thuringian Forest and the Thuringian Slate Mountains (Germany). At four study areas, 48 plots with manually enriched FWD were paired with 48 nearby control plots without added woody debris. Soil moisture and soil, surface and near-ground air temperature were recorded with TOMST TMS-4 dataloggers from May to August 2024. Vegetation cover was visually estimated in 50 cm radius plots around the dataloggers. Linear mixed-effects models and, for the vegetation cover, a generalized mixed-effects model with a beta regression were used to test for differences between FWD and control plots. FWD enrichment significantly increased volumetric soil water content by about 4.5 percentage points compared to control plots. Mean and maximum soil temperatures were reduced on FWD plots, and surface temperatures showed buffering. Mean values were lower, daily maxima decreased by more than 4 °C and daily minima increased about 1.4 °C. Effects on near-ground air temperature at 15 cm height were weaker but indicated slightly cooler maxima and higher minima. Total vegetation cover declined from roughly 75% on control plots to about 51% on FWD plots. These results show that local FWD enrichment can create cooler, moister and less densely vegetated microsites on Norway spruce calamity areas. However, further research is needed to test whether the observed changes in microclimate and vegetation translate into improved germination, survival and growth of natural and artificial regeneration in these specific conditions.
Hans Großgott (Wed,) studied this question.