The influence of storm-induced microsites to tree regeneration patterns in boreal and hemiboreal forest

We reviewed studies dealing with regeneration under variable conditions in boreal and hemiboreal forests as affected by different microsite types by tree species functional groups. Generally, the importance of storm-induced microsites for regeneration dynamics in boreal forests depends on several factors: (1) distribution and type of microsites (generated by storm characteristics and stand conditions); (2) viable seed supply (stand history, species dispersal traits and status of surviving trees) and their species' life history strategy; (3) climatic and site conditions (pre-storm conditions and storm-induced changes); and (4) delayed storm effects, such as retarded falling of trees, favoured vegetation growth, etc. Studies acknowledging the significance of microsites were mostly related to intermediate or severe events, causing sufficient changes in resource levels and growth conditions, and influencing extrinsic factors such as frost heaving, erosion and browsing. Also, the dispersal traits of available tree species, including sprouting and response of surviving trees, such as canopy expansion, should be considered in evaluating microsite importance in individual cases. In intermediate to severe windstorm events, pioneer species are generally profiting most from the additional offer in microsites, requiring bare mineral soil and elevated locations for their establishment and growth. Under gap dynamics, shade-tolerant species benefit from dead wood and elevated locations as these offer safe sites in stands with abundant understorey vegetation.