Limited scientific information is currently available regarding saproxylic fungal communities in the boreal forest of North America. We aimed to characterize the community development, richness and activity of saproxylic fungi on fresh wood in harvested and unmanaged boreal mixedwood stands of northwestern Québec (Canada). Fresh wood blocks (n = 480) of balsam fir (Abies balsamea (L.) Mill.) and trembling aspen (Populus tremuloides Michx.) were placed on the forest floor in a range of stand conditions (n = 24). Blocks were harvested every 6 months for up to 30 months and characterized for species composition and richness (PCR-DGGE, DNA sequencing), respiration, wood density and lignin and cellulose content. Colonization by a wide range of functional groups proceeded rapidly under different stand conditions. We detected a total of 35 different fungal operational taxonomic units, with the highest species richness at the wood block level being observed within the first 12 months. No differences in community composition were found between wood host species or among stand conditions. However, the variability in fungal communities among blocks (? diversity) was lower on trembling aspen wood compared with balsam fir and decreased over time on trembling aspen wood. Also, fungal activity (respiration and wood decomposition) increased on trembling aspen wood blocks and species richness decreased on balsam fir wood over time in partial-cut sites. The overlap in tree composition among stands, the high volume of logs and the recent management history of these stands may have contributed to the similarity of the saproxylic fungal community among stand types and disturbances. © 2014 Springer-Verlag Berlin Heidelberg.

Les chicots et les billes au sol sont des composantes substantielles du réservoir de carbone détritique en forêt boréale. Les effets de leur décomposition sur les caractéristiques physiques et chimiques de la couverture morte restent méconnus. Le principal objectif de cette étude était de caractériser les transformations chimiques des billes et des chicots en décomposition d’espèces d’arbres communes en forêt boréale mixte. Des billes et des chicots de différentes classes de décomposition ont été échantillonnés et analysés par résonance magnétique nucléaire du 13C en phase solide et par spectroscopie dans le proche infra-rouge. Des changements chimiques faibles ou modérés apparaissaient dans les billes et les chicots frais ou modérément décomposés, mais dans les billes bien décomposées, une dégradation substantielle des hydrates de carbone et une augmentation de la concentration en lignines avaient lieu. Les espèces décidues avaient initialement plus d’hydrates de carbone que les conifères, mais la décomposition réduisaient leurs différences, et dans les billes bien décomposées, les espèces ne différaient que par leur teneur en lignines. Les billes bien décomposées des espèces décidues atteignaient des densités de bois très faibles, et leur intégration dans la couverture morte et leur préservation à long-terme restait questionnable. Au contraire, la composition chimique des billes bien décomposées de conifères ressemblait à celle de la couverture morte lignique (c’est-à-dire la couverture morte provenant de la décomposition du bois mort), avec préservation des lignines, des hydrates de carbone et des composés alkylés. Le bois décomposé de conifères contribue à l’hétérogénéité chimique de la couverture morte, favorisant la diversité des décomposeurs et la rétention du carbone dans les sols.

Environmental change, including human disturbance, can have a striking impact on the biodiversity of ecosystems. We used a molecular fingerprinting technique to determine how communities of saproxylic fungi on trembling aspen deadwood change under the influence of silvicultural treatments designed to emulate natural stand dynamics. We describe changes in richness, diversity, and species composition of fungal communities of trembling aspen logs and snags caused by these silvicultural practices. Our study was conducted in the SAFE Project, a series of silvicultural experiments that tests an ecosystem management model based on natural dynamics. We found that large trembling aspen logs and in advanced decay stages had approximately 9% higher fungal species richness and 10% higher fungal diversity than small and large logs at medium decay stages. The effect of log diameter was in turn strongly dependent on the silvicultural treatment. In burned stands, larger logs supported higher fungal richness and diversity, therefore potentially acting as fungal refuge. A negative relationship between the fungal diversity of logs and snags and the volume of fine woody debris was also related to silvicultural treatments, as fine woody debris increased with silvicultural intensity. Our results underline the negative effects of intense silvicultural practice on fungal diversity and species richness by modifying community composition, but they also highlight the benefits of partial harvest, which retain coarse woody debris volume.

Coarse woody debris supports large numbers of saproxylic fungal species. However, most of the current knowledge comes from Scandinavia and studies relating the effect of stand or log characteristics on the diversity and composition of decomposer fungi have not been conducted in Northeastern Canada. Logs from five tree species were sampled along a decomposition gradient in nine stands representing three successional stages of the boreal mixed forest of Northwestern Quebec, Canada. Using a molecular fingerprinting technique, we assessed fungal community Shannon–Weaver diversity index, richness, and composition. We used linear mixed models and multivariate analyses to link changes in fungal communities to log and stand characteristics. We found a total of 33 operational taxonomic units (OTUs) including an indicator species for balsam fir (similar to Athelia sp.) and one found only in aspen stands (similar to Calocera cornea). Spruce logs supported the highest fungal Shannon–Weaver diversity index and OTU number. Our results support the hypothesis that log species influences fungal richness and diversity. However, log decay class does not. Stand composition, volume of coarse woody debris, and log chemical composition were all involved in structuring fungal communities. Maintaining the diversity of wood-decomposing communities therefore requires the presence of dead wood from diverse log species.