Bryophyte species assemblages in fire and clear-cut origin boreal forests

Abstract

Natural and anthropogenic disturbances could have different impacts on understory plant communities. Investigating these differences could help improve silvicultural and management practices in order to better achieve biodiversity protection objectives. Using post-fire (20–90years) and post-clearcutting (20–70years) forest chronosequences placed on similar sites, we examined which environmental factors are the main drivers of bryophyte community assembly in eastern Canadian boreal forests, using information on bryophyte life-history strategies (colonist: high reproductive effort but a short potential life span; perennial: low reproductive effort and a long potential life span) to interpret the resulting patterns. The fire origin stands were affected by high-severity fires followed by natural regeneration, whereas the clear-cut stands were regenerated through the advance regeneration present in the understory of the harvested stands. Our results indicate that by killing the existing mosses and baring the mineral soil, fire tends to decrease the cover of perennial species (such as Pleurozium scherberii) and increase the presence of colonist species compared with clear-cut. Overall species richness does not increase much in older stands, but some species that have been identified by previous studies as being more sensitive to management activities, such as liverworts, tend to be strongly associated with balsam fir basal area, which is higher in mature clear-cut origin stands. This tree species tends to be heavily affected by partial mortality events after >50years (insect outbreaks, windthrow), which could accelerate the creation of heterogeneous canopy structure and generate a greater diversity of microhabitats suitable for sensitive bryophyte species. More research needs to be conducted to better understand the underlying functional relationships between overstory tree composition and bryophyte communities.