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The spruce budworm, Choristoneura fumiferana, is presumed to be panmictic across vast regions of North America. We examined the extent of panmixia by genotyping 3,650 single nucleotide polymorphism (SNP) loci in 1975 individuals from 128 collections across the continent. We found three spatially structured subpopulations: Western (Alaska, Yukon), Central (southeastern Yukon to the Manitoba–Ontario border), and Eastern (Manitoba–Ontario border to the Atlantic). Additionally, the most diagnostic genetic differentiation between the Central and Eastern subpopulations was chromosomally restricted to a single block of SNPs that may constitute an island of differentiation within the species. Geographic differentiation in the spruce budworm parallels that of its principal larval host, white spruce (Picea glauca), providing evidence that spruce budworm and spruce trees survived in the Beringian refugium through the Last Glacial Maximum and that at least two isolated spruce budworm populations diverged with spruce/fir south of the ice sheets. Gene flow in the spruce budworm may also be affected by mountains in western North America, habitat isolation in West Virginia, regional adaptations, factors related to dispersal, and proximity of other species in the spruce budworm species complex. The central and eastern geographic regions contain individuals that assign to Eastern and Central subpopulations, respectively, indicating that these barriers are not complete. Our discovery of previously undetected geographic and genomic structure in the spruce budworm suggests that further population modelling of this ecologically important insect should consider regional differentiation, potentially co‐adapted blocks of genes, and gene flow between subpopulations. [ABSTRACT FROM AUTHOR]

• Recovery in absence of treatments showed the resilient nature of mixedwood stands. • Understory conifers largely contributed to recovery of stand basal area and vigor. • Active rehabilitation could speed improvement of composition, quality and structure. • Shelterwood combined to scarification during good seed year is recommended. • Prescriptions should include provision of conifers in lower and upper strata. In northeastern North America, mixed hardwood-conifer forests have commonly been harvested with selective practices such as diameter-limit cutting. By removing trees of highest commercial value, these cuts often left stands with highly variable density and reduced volume, less species diversity, and lower wood quality. The lack of care to the regenerating layer also resulted in regeneration deficiencies, especially on productive sites supporting yellow birch (Betula alleghaniensis Britton)-conifer stands. We assessed the 15-yr effects of four rehabilitation scenarios on stand growth, quality, vigor and regeneration in an experiment established in Quebec, Canada. The trial compared untreated experimental units (e.g. control), uniform shelterwood method (50 overstory trees/ha), strip clearcutting (20-m strips), and seed-tree method (10 overstory trees/ha), all combined with 3 site preparation treatments (no scarification, mechanical raking, and spot scarification). After 15 years, the ongoing recovery of growth, vigor and regeneration in the control and untreated part of the strip clearcut plot reflected the resilient nature of these mixedwood stands, with conifer (Abies balsamea [L.] Mill. , Picea rubens Sarg., Picea glauca [Moench] Voss) saplings and poles contributing to the recovery of total BA and that of vigorous trees (i.e. acceptable growing stock [AGS]). The control and strip clearcut treatments, however, had high BA of unacceptable growing stock. Shelterwood plots recovered more slowly in BA and AGS, but had greater BA of high-quality trees than the control. Seed-tree method was less optimal because of its slow recovery and high understory competition. The lack of synchronization with a good seed year limited the efficiency of scarification, and increased the abundance of non-commercial species. An active rehabilitation strategy combining shelterwood system and ground disturbance (e.g. raking) during a good seed year should help to improve stand quality and regeneration. Yet, our results indicate that retaining conifers in the understory and overstory would ensure a seed source and accelerate recovery. Where seed sources and conifer advance regeneration are lacking, enrichment planting may be necessary to maintain a mixedwood composition over time. [ABSTRACT FROM AUTHOR]