Final report (2022)
The aim of the project was to assess the dynamics of ecosystem processes (deadwood decomposition, changes in the properties of deadwood and soil, changes in vegetation) after single and mass windthrow in broad-leaved forests by the example of the Kaluzhskie Zaseki State Nature Reserve, where both single windfalls and mass windfalls of 2006 are present. Field work was carried out at two sites of mass windfalls: in fluvio-glacial sands (near the village of Yagodnoe) and in sandy-loams (near the village of Nagaya), as well as in an old-growth forest near the former village of Trud, where isolated windfalls often occur. We sampled 220 wood samples from the trunks of 8 tree species at different decay stage; 128 soil samples on sands and sandy-loams at windfall sites (under and next to dead wood of 8 tree species) and in the background forest communities; and over 500 samples of basidiomycetes on dead wood of 8 tree species; we registered dead wood volume and undergrowth on the plots, which were established in 2010. The samples were analyzed in laboratories; statistical analysis of the results was performed.
It was shown that the presence of fallen large (over 40 cm in diameter) oak logs significantly affects the species richness and composition of herbaceous and woody plant species in a mesic Quercus forest. An increase in the overall species richness of an old-growth forest is achieved by successful establishment and growth on deadwood boreal and meadow-grassland plant species, which are considered atypical for broadleaf forests.
At the sites of mass windfall, despite the predominance of Populus tremula in the first years after the event, in 15 years there is formed a plant community close to the original composition with the participation of Acer platanoides, Tilia cordata, Populus tremula, Ulmus glabra, Fraxinus excelsior, and A. campestre, except for Quercus robur and Picea abies completely missing in the new tree generation.
The characteristics of bulk density, C and N content and pH in deadwood at five decomposition stages were analyzed for 8 tree species (Quercus robur, Fraxinus excelsior, Tilia cordata, Acer platanoides, Ulmus glabra, Populus tremula, Picea abies and Betula pendula). In general, for all samples, wood density did not correlate with trunk diameter, did not differ between tree species, and linearly significantly decreased with increasing decomposition stage. Species did not differ in N content, C/N ratio, but did differ in C content and pH value. Decomposition stages had a greater effect on wood characteristics compared to species identity. This was observed for all tree species and for all traits except for carbon content, which practically did not change during decomposition and averaged 45.8%. Trend analysis showed that the data mostly agreed well with linear models: as the decomposition stage increased, the nitrogen content increased significantly and the C/N ratio decreased significantly. The change in pH was best explained by the quadratic model: the values during decomposition first decreased and then increased.
We propose a method for calculating wood decomposition rates for data collected at a mass windfall. The difference in decomposition rates between species with a common fall time of all trunks is reflected in the different proportion of wood at different decomposition stages in different species. We estimated this by the area of wood at different decomposition stages on cross-sections. According to decomposition rate, tree species were ranked in descending order from diffuse-porous (Populus tremula, Betula pendula, Tilia cordata, Acer platanoides) to ring-porous (Ulmus glabra, Fraxinus exelsior, Quercus robur) deciduous species; coniferous species Picea abies was at the end of the diffuse-porous species series.
Differences in the impact of mass windfalls in multispecies broadleaved forest on soil properties in sands and sandy-loams were revealed. On sandy-loams, many indicators of activity and soil richness were maximal at the mass windfall site, but not under fallen trunks, but next to them; in general, a significant increase in cation exchange capacity and decrease in soil acidity occurred at mass windfall on sandy-loams. On sands, soil enrichment at a mass windfall area appeared as a decrease in the C/N ratio and an increase in the microbiological activity of soils: an increase in the content of microbial biomass and basal respiration rate. We also observed a stronger dependence of soil characteristics on the fallen tree identity; properties of soil samples taken directly under the logs and next to them differed little.
In the mass windfall area on sands, 100 species of aphyllophoroid basidomycetes were identified on eight trunks and 33 cross-sections of eight tree species by their fruiting bodies. Of the 100 species, 52 were rare for European Russia and 46 species were new to the Kaluga Region. Sixty-two basidiomycete species were found in the mass windfall area on sandy-loams, including 20 new species in the Kaluga Region; seven fungi species were not found in the site on sands. New locations of the rare species Aurantiporus croceus, confined to large dead oak trees in old-growth broad-leaved forests and included in the Red Book of Kaluga Region (2015) and the IUCN Red List of Endangered Species were registered in the vicinity of the former village of Trud. The distribution of fungal species by xylolysis types detected at the windfall site on sands showed the predominance of white rot fungi (78%) over brown rot fungi (22%); for the site on sandy-loams, this ratio was 84 and 16%.
