White pine decline in managed forests has led to the adoption of ecosystem-based management using natural disturbances, mainly surface fire. However, other natural disturbances, such as spruce budworm (SBW), are present in the native range of white pine but are rarely considered in the management of this species. SBW outbreaks are expected to change in frequency and severity under climate change, increasing the need to understand if and how this disturbance will affect the dynamics of white pine regeneration. In this study, we evaluated the impacts of an SBW outbreak on white pine and balsam fir regeneration and identified environmental variables that affect regeneration dynamics. We evaluated six defoliated and six control study plots in white pine stands close to the northern limit of the Québec’s temperate forest. In each plot, we counted white pine and balsam fir seedlings and measured structural (diameter, height), and abiotic (gap fraction, soil type) variables. White pine seedling density was three times greater in defoliated plots than in controls. By contrast, there was no significant difference in balsam fir seedling density between disturbance types. Seedlings of both species were taller in defoliated plots than in control plots. Overall, the SBW outbreak promoted white pine seedling density and height growth. This research contributes to our understanding of the effects of SBW outbreaks on white pine regeneration dynamics, and it will help forest managers to select harvesting methods that emulate SBW-modulated stand characteristics.

Mixed-species plantations are widely recognized for enhancing understory biodiversity compared to monospecific stands; however, most evidence comes from conifer-deciduous mixtures. Thus, it remains unclear whether intraspecific mixtures, such as polyclonal plantations, can harbor greater understory vegetation diversity than monospecific plantations. This study evaluated how monoclonal (one clone) and polyclonal (four clones) hybrid poplar (Populus spp.) plantations influence the taxonomic and functional diversity and composition of understory vegetation. We selected four hybrid poplar clones planted in monoclonal or polyclonal blocks across three sites of contrasting environmental conditions and land-use histories in northwestern Québec, Canada. We assessed understory vegetation (vascular plants, bryophytes, and lichens) diversity and composition and quantified vascular plant functional diversity. Polyclonal plantations supported higher vascular plant functional diversity than monoclonal plantations at the sites established on abandoned agricultural land. In contrast, functional diversity did not differ between plantation types at the previously forested site, likely due to strong environmental filtering and legacy effects of prior forest cover. Community functional composition was mainly driven by land-use history and latitude: the forest site was associated with more competitive, late-successional strategies, whereas abandoned farmlands favored more acquisitive and spatially expansive traits, and conservative traits increased toward higher latitudes. Overall, plantation type and site conditions jointly shaped understory community composition. These results underscore the ecological relevance of clonal mixing for plantation management and biodiversity conservation, while highlighting the importance of site context in modulating the effects of plantation design.