The southern portions of the boreal region across Canada are dominated by boreal mixedwoods forests, which are characterized by varying canopy dominance of boreal broadleaf and conifer trees. This forest region encompasses a large east-to-west gradient of climate and disturbance regimes. Although the same major boreal tree species occur in all parts of the boreal mixedwood region, they vary greatly in relative abundance. This is a reflection of the interactions among the different abiotic and biotic components. As a result, there is considerable variation in post-disturbance stand development, producing a wide variety of mixedwood forest conditions existing as a mosaic in time and space. Post-disturbance dominance by broadleaf species followed by a transition to conifers is the "classic" pathway in all regions. However, there is wide variation in the transition rate and the species sequence across the gradient depending on factors such as moisture, abundance of each species, fire cycle, climate and secondary disturbances (mainly insect outbreaks). Future changes in climate and disturbance regime could influence the nature of stand dynamics of boreal mixedwoods and the prominence of different pathways among regions. Focussing on the commonality of processes in mixedwood stand development across the boreal is a promising way to address the management of this important forest ecosystem.Keywords: Canadian boreal mixedwood forest, stand dynamics, fire disturbance, insect disturbance, forest management emulating natural stand dynamics RÉSUMÉ Le sud de la région boréale canadienne est dominé par la forêt boréale mixte, caractérisée par une canopée à dominance feuillue et coniférienne en différentes proportions. Cette région forestière traverse d' est en ouest, un large gradient climatique et différents régimes de perturbation. Les espèces principales de la forêt boréale mixte sont les mêmes à travers le Canada, mais leur importance relative varie. Cela reflète les interactions entre les différentes composantes biotiques et abiotiques de l' écosystème. Le développement d'un peuplement après perturbation peut prendre différentes tangentes ce qui fait qu'il existe plusieurs types de forêts boréales mixtes qui se présentent sous forme de mosaïques spatiales et temporelles. Une dominance feuillue après perturbation, suivie d'une transition vers les conifères, constitue la séquence temporelle « classique » de la dynamique forestière dans toutes les régions. Toutefois, les taux de transition et les séquences d' espèces varient grandement à travers le gradient. Cette variabilité dépend principalement du régime d'humidité, de l'abondance de chaque espèce, du cycle de feu, du climat et des perturbations secondaires (surtout les épidémies d'insectes). Les changements climatiques futurs et le régime de perturbations pourraient influencer la nature de la dynamique des peuplements de la forêt boréale mixte et l'importance relative des différents patrons temporels à travers les régions. Bien comprendre les processus communs a...

Aims: In the boreal mixedwood, fire initiates forest succession; however, over time other disturbances such as insect outbreaks cause pulses of mortality and opportunities for recruitment of shade-intolerant species. Questions: What are the respective roles of time since fire and insect outbreaks in driving directional, vs cyclical and retrogressive succession? Do assessments from direct measurements and chronosequence approaches converge? We hypothesise that the chronosequence approach will accurately characterise large-scale compositional patterns especially in younger stands and that direct measurements will better describe small-scale, non-directional changes in succession. Location: Boreal mixed wood of northwestern Quebec (79°1′ W, 48°30′ N). Methods: We sampled 469 plots over an 18-year interval (in 1991 and 2009) in mixed hardwood/conifer forests to observe in situ the changes in stands having originated from seven fires covering a 249-year chronosequence. Results: The combination of the remeasurement and chronosequence analyses validates predictions of forest succession. Our results indicate that time since last fire is the dominant factor explaining forest succession for the first 150 years after fire and globally at the scale of the entire forest, although smaller-scale disturbances such as spruce budworm outbreaks can change the course of forest succession, especially at stand scales. Conclusion: While time since fire is the dominant driver of forest succession in younger forests, secondary disturbances, such as spruce budworm outbreaks, can advance or reverse forest succession in older forests. This study also serves as a validation of the overall patterns described in spatial chronosequence approaches at the landscape level in fire-dominated systems but highlights that local succession may deviate from the overall pattern especially in older forests or in forests affected by non-stand re-initiating intermediate disturbances.