Management legacy in the understory of North American mixed boreal regenerating stands

•Taxonomic and functional assemblages differed between stand types.•Planted stands were characterized by species and traits typical of younger stands.•Planted stands may have lower conservation potential than naturally regenerated stands.

In the global context of planted forest expansion, the ability of artificially regenerated forests to stand-in for natural forests has become a central question for forest managers. Although few studies have examined their conservation potential, extensive planted forests cover a significant portion of North-American mixed boreal forests. We study the composition, functional assemblage, and vertical structure of understory communities in even-aged, mid-rotation, planted and naturally regenerated mixed boreal stands typical of extensive management (Québec, Canada). Our results show that more than 20 years after harvest, species composition and functional assemblage still differ between stand types while understory structure does not. Planted stands exhibit a higher prevalence of traits and species typically associated with younger stands. Sensitive species such as Oxalis acetosella ssp. montana and Monotropa uniflora occurred less often in planted stands while the reverse was true for a portion of species with the potential to form a recalcitrant layer. This suggests that the understory of planted sites may require more time before reaching compositional and functional attributes comparable to those of naturally regenerated stands. This delayed maturation has implications for forest management, particularly under increased management intensity scenarios.