Morgane Henry, Patrick James, Daniel Kneeshaw, Brian Leung. Connecting the dots: elucidating the relationship between spruce budworm population dynamics and defoliation 2026. Can. J. For. Res. 1
DOI : 10.1139/cjfr-2025-0197
Spruce budworm (Choristoneura fumiferana) outbreaks are a major disturbance in northeastern American forests. Monitoring, forecasting, and mitigating outbreak risks require information on how local population densities translate to defoliation. Given landscape-scale heterogeneity, forest structure, and local population dynamics, one expects the relationship between population densities and defoliation to vary spatially and temporally. We analyzed 17 years of larval density data from over 1000 locations in Québec, Canada, to investigate how larval densities and environmental context translate into observable defoliation. We found a positive latitudinal gradient and a positive effect of hardwood species on insect population growth rates. Further, we identified a 3-year cumulative effect of larval densities on defoliation, with a 2-year lag having the strongest influence. On average, a density of 15 larvae per branch corresponded to a 29% probability of defoliation. However, this probability varied widely (13%?52%) with the proportions of balsam fir and black spruce. Our study elucidates the relationship between SBW populations and defoliation, highlighting the importance of cumulative larval density effects and environmental context in defining defoliation risk.
S. Ellen Macdonald, Anne C. S. McIntosh, Selena Schut, Samuel Bartels, Seung-Il Lee, Elvira Baisheva, Jeff Battigelli, Erin Bayne, Yves Bergeron, Mathieu Bouchard, Brendan Casey, Mats Dynesius, Tanya Handa, Joakim Hjalten, Kristoffer Hylander, Matti Koivula, Jari Kouki, Therese Löfroth, Asko Lõhmus, Anders Nielsen, Sonya Odsen, Manuela Panzacchi, Jaime Pinzon, Peter B. Reich, Pavel Shirokikh, Ekaterina Shorohova, Ilkka Vanha-Majamaa, Lisa Venier, Timothy Work, Linhao Wu. Biodiversity recovery is slow following clear-cut harvest of boreal forests 2026. Nat Sustain s41893-026-01868-x
DOI : 10.1038/s41893-026-01868-x
Boreal forests are important reservoirs of biodiversity, carbon and timber stocks. However, timber harvest can alter biodiversity in these forests without clear evidence on the duration needed for biotic groups to recover. Resilience of boreal forest biodiversity to clear-cut harvest was examined with a meta-analysis of 190 datasets from boreal and hemi-boreal forests of Europe/Russia and North America for arthropods, birds, small mammals, lichens, bryophytes and vascular plants. We modelled similarity of community composition between harvested and unharvested stands versus years post harvest. In approximately half of cases, predicted times for recovery to pre-harvest composition were ≤30 years. In other cases, recovery took much longer or had not occurred within the timeframe of our data; for example, in conifer forest: >100 years (bryophytes), >55 years (small mammals), ~95 years (lichens) and ~85 years (vascular plants). Saproxylic beetles showed no resilience within the 16 (conifer forest) or 29 (mixed forest) years post harvest for which we had data. Recovery generally took longer in conifer and mixed than in broadleaf forests, which always showed either resistance (bryophytes, vascular plants) or resilience with recovery within 12–25 years. Conserving biodiversity in boreal forests will require extended rotations, management for ‘old forest’ structural elements and areas protected from harvesting.
