Can partial harvesting in boreal mixedwoods maintain processes and fungal communities associated with coarse woody debris? Manuella Struckelj Hedi Kebli Suzanne Brais
Acknowledgements
Presentation plan Why deadwood? Hypotheses The Canadian boreal mixedwoods The SAFE project Methods Deadwood dynamics and C pools Wood-inhabiting fungal community Conclusion
Why deadwood? Supports more heterotrophic biomass and diversity than live trees; Scarcity of dead organic matter in managed forests is the leading cause of decreases in species diversity Contributes to the structural heterogeneity of the forest floor. Long-term pool of carbon and nutrients.
Hypotheses Partial harvesting will maintain C pools and dynamics within the limits of those of natural stands. By maintaining higher substrate availability, partial harvesting will mitigate the negative effects of harvesting on saproxylic fungal species richness and species composition.
The Canadian boreal mixedwoods Boreal mixedwoods are highly productive More diverse than Fennoscandian boreal forests Human impact relatively recent
Harvey et al fire intolerant hardwoodsmixed stands softwood dominated stands Insect outbreak insect outbreak fire Time since last stand-replacing fire pionneer species hardwoods mixed stands softwood dominated stands clear cut partial cut clear cut partial cut selection cut even-aged silviculture uneven-aged silviculture
Ecosystem-based silviculture in aspen- dominated stands (SAFE 1) Control burn Clear cut Control Low thin 31 % BA High thin 60 % BA
Monitoring C pools and fluxes
191 logs (aspen) 48 snags (aspen) DNA extraction, cloning and sequencing Snag and log characteristics Stand deadwood volume Characterisation of wood-inhabiting fungi community
Effects of partial and clear-cut harvesting on aboveground C pools associated with trees, snags, and downed logs. Live treesSnagsLogs Time since harvesting
Nine year cumulative C fluxes to dead organic matter associated with leaf litterfall and tree death.
Effects of partial and clear-cut harvesting on decomposition of leaf litter and wood of trembling aspen.
Effect of partial and clear-cut harvesting on C pools over a 9-year period following harvesting
Harvesting prescriptions modified deadwood characteristics Small logs Mid-decayed logs Well decayed logsLarge logs
Fungal communities on aspen snags and logs 35 different operational taxonomic units (OTU) were found on logs, 31 on snags. Mean number of OTUs per log = 5.5 (maximum of 20) Mean number on snags = 5.4 (maximum of 12) Resinicium bicolor and Phialophora sp. were found predominantly on snags Athelia neuhoffii, Phellinus cinereus, Calocera cornea on logs
Fungal richness on deadwood is linked to both log/snag and stand characteristics Effect of stand and log characteristics on richness (number of OTUs). Model averaged estimates and unconditional standard errors were obtained from linear mixed multimodel inference. Explanatory variable Model averaged estimate Unconditional SE Type of deadwood Logs Small fresh logs Large fresh logs SnagsFine woody debris volume
Large logs had the highest rrichness and the effect was more pronounced in highly disturbed stands Independent of harvesting intensity, large well-decayed logs (>10 cm) had the highest richness. + nearly 2 OTUs (10%) compared to small mid-decayed logs OTUs (7.5%) compared to large, mid-decayed logs Negative values indicate that fungal species richness was higher on small logs while positive values indicate that more OTUs were found on large logs.
Conclusion Carbon dynamics after partial cutting conserved many characteristics of natural stands Partial harvesting prescription has incidence on deadwood abundance and recruitment Wood inhabiting fungal community responds to changes in deadwood abundance and size distribution. The most severe disturbances affect fungal species richness Specific objectives (recruitment, abundance, size) can be incorporated into partial harvesting prescriptions Large logs can buffer adverse environmental conditions following disturbance