Forest structure and understory plant communities inside and outside tree retention groups in boreal forests

Abstract

Alternatives are being sought to the widespread use of clear-cut logging in boreal forests. Group retention harvesting is a silvicultural treatment in which well-distributed but relatively small residual forest patches (ca 10 m wide) are left inside cutover sites. The objective of this study was to compare vascular plant communities, tree species regeneration, and dead wood retention in tree retention groups and adjacent clear-cuts with soil protection. Our results indicate that plant diversity is relatively similar inside tree retention groups and the adjacent clear-cut area. This result may be explained by the important spatial variability observed among the stands, which were located in different geographical locations, the fact that soils were little disturbed during harvesting in clear-cuts and few opportunities were present for the establishment of pioneer species, and the relatively short time span since harvesting. Using a functional trait approach, we found that shade tolerance still plays a significant but relatively minor role in explaining species abundance between the 2 environments. Tree retention groups also retain a greater quantity and greater variability of dead wood materials compared with clear-cuts, and a higher abundance of regenerating trees, which is likely explained in part by the direct damage caused by the harvesting operations outside tree retention groups. Overall, retention groups do not appear to confer superior protection for late-successional plants compared with traditional clear-cut logging with soil protection. Their ecological value mostly consists in ensuring a minimal input of dead woody materials for saproxylic species.