Regeneration dynamics after fire and clear cutting in boreal mixedwoods.

摘要

Emulation of natural disturbance processes and their effects is important to maintain the structure and composition of managed forests. In boreal mixed forests, clearcutting has been considered as management practice suitable to mimic stand-replacing fire as both disturbances create conditions of high light availability.To examine whether logging and fire have different effects on natural regeneration of six common boreal tree species (Populus tremuloides, Betula papyrifera, Pinus banksiana, Picea mariana, P. glauca, and Abies balsamea), density and mean annual height growth of tree regeneration after fire and clearcutting in northern Ontario was studied. Regeneration densities of all studied species, except P. glauca and A. balsamea, were positively related to their respective pre-disturbance basal area. Post-disturbance regeneration densities and mean annual height growth of P. tremuloides and P. banksiana did not differ between disturbance types, whereas those of B. papyrifera were higher after fire, and those of P. mariana and A. balsamea were higher after clearcutting. Compared with fire, clearcutting significantly increased the post-disturbance presence of A. balsamea, which is attributed to surviving advance regeneration after logging. The natural regeneration process after fire in terms of regeneration density appears to be emulated by clearcutting for P. tremuloides, P. banksiana, P. mariana, and P. glauca, but the increase of B. papyrifera after clearcutting is less pronounced than after fire, while the reduction of Abies balsamea after clearcutting is less severe than after fire. Survival of advance regeneration likely caused higher mean annual growth of A. balsamea and P. mariana.The vertical and horizontal structural diversity of live trees was similar following both disturbance types, but species diversity was higher after clearcutting. This increase was attributed to survival of late-successional conifers. All stand-replacing disturbances promote broadleaves, but succession may be accelerated in clearcuts because of the survival of advance regeneration.Key words: regeneration strategy, shade-tolerance, tree regeneration, fire, clearcutting, boreal mixedwoodsTo examine how species with certain regeneration strategy and shade-tolerance respond to different disturbances, a meta-analysis was performed by collecting published data of pre- and post-disturbance stand compositional characteristics in the northern forests. The direct regeneration hypothesis (DRH), which suggests that tree communities will be restored with the same pre-disturbance composition within a few decades after a stand-replacing disturbance (Yih and others, 1991), was tested based on species responses to disturbances. All disturbances promoted broadleaved species regardless of regeneration strategy (suckering, sprouting, or seeding). The DRH was supported by conifers with serotinous cones after fire. Fire caused local extinction of non-serotinous conifers, while wind and clearcutting only decreased the proportion of non-serotinous conifers due to partial survival of seed sources and advance regeneration. The meta-analysis revealed a lack of available data to analyze response of serotinous and semi-serotinous species to clearcutting.