Abstract Aim Seedling recruitment is a vital process for forest regeneration and is influenced by various factors such as stand composition, climate, and soil disturbance. We conducted a long-term field experiment (18?years) to study the effects of these factors and their interactions on seedling recruitment. Location Our study focused on five main species in boreal mixed woods of eastern Canada: trembling aspen (Populus tremuloides), paper birch (Betula papyrifera), white spruce (Picea glauca), balsam fir (Abies balsamea), and white cedar (Thuja occidentalis). Methods Sixteen 1-m2 seedling monitoring subplots were set up in each of seven stands originating from different wildfires (fire years ranging from 1760 to 1944), with a soil scarification treatment applied to every other subplot. Annual new seedling counts were related to growing-season climate (mean temperature, growing degree days and drought code), scarification, and stand effects via a Bayesian generalized linear mixed model. Results Soil scarification had a large positive effect on seedling recruitment for three species (aspen, birch and spruce). As expected, high mean temperatures during the seed production period (two years prior to seedling emergence) increased seedling recruitment for all species but aspen. Contrary to other studies, we did not find a positive effect of dry conditions during the seed production period. Furthermore, high values of growing degree days suppressed conifer seedling recruitment. Except for white cedar, basal area was weakly correlated with seedling abundance, suggesting a small number of reproductive individuals is sufficient to saturate seedling recruitment. Conclusion Our findings underscore the importance of considering multiple factors, such as soil disturbance, climate, and stand composition, as well as their effects on different life stages when developing effective forest management strategies to promote regeneration in boreal mixed-wood ecosystems.

A combination of wildfires and defoliating insect outbreaks play an important role in the natural successional dynamics of North American boreal mixedwood forests, which, in the long term, change the post‐disturbance composition and structure of forest stands. After stand‐replacing disturbances (mainly wildfires), early successional hardwoods typically dominate the affected areas. Provided enough time following disturbances, the increasing recruitment of mid‐ to late‐successional softwoods as well as the mortality of hardwoods gradually change forest composition from hardwoods to admixtures of hardwood‐conifer species and conifer‐dominated stands in mid and late successional stages, respectively. Such mixedwoods are abundant across the southern Canadian boreal forest. In boreal Canada, mixedwoods are the most structurally heterogeneous forest ecosystems, are highly productive, and form an important source of timber supply. Here we present the EASTERN BOREAL MIXEDWOODS CANADA data set, which documents the changes in composition and structure of stands originating from eight different wildfires representing a chronosequence of 249 yr since fire in eastern Canada. This data set has been used in several different projects to study and model the influence of natural (e.g., insect outbreaks) and anthropogenic disturbances (e.g., harvesting) on the dynamics of post‐fire stands. The data set covers a high range of variability in stand composition and structure, explained by species establishment, dominance, and mixture. It thus constitutes a useful source of information to trace the dynamics of the main boreal tree species of eastern North America, from their establishment to their replacement at different spatial scales (e.g., from stand to landscape level). Please cite this data paper when the data are used in publications. We also request that researchers and teachers inform us of how they are using the data. We are open to collaborate in developing or co‐authoring relevant research projects based on this data set.

La sécurité une affaire de tous

Ce guide ne remplacera jamais une formation adéquate pour l’utilisation de l’équipement dont vous avez besoin et pour l’organisation de votre échantillonnage. Il a pour but de vous amener à prendre conscience des règles de base qui vous aideront à assurer une saison de terrain sécuritaire et agréable. Quels que soient le genre de travail et la région où vous travaillez sur le terrain, rappelezvous, une attitude sécuritaire et consciencieuse est le seul moyen de prévention efficace contre tout danger. Une saison de terrain sécuritaire n’est pas seulement une question de chance.

This paper presents a synthesis of the dendroecological work conducted in the area of Lake Duparquet in the southern boreal forest of northwestern Quebec (Canada) during the last 15 years. The topics of these syn- and autecological studies encompassed forest dynamics and tree growth related to natural disturbances such as forest fires, insect outbreaks, and flooding, as well as the effects of climate change. Seven major fire events occurred around Lake Duparquet since 1720: 1760, 1797, 1823, 1847, 1870, 1916, and 1944. Post-fire stand dynamics, established by a chronosequence of over 200 years, are characterized by the gradual transition from broadleaf dominated stands towards mixed and finally almost pure conifer stands. After fire, insect outbreaks are the second most important disturbance type in the southern boreal forest. Spruce budworm, the predominating defoliating insect, but also forest tent caterpillar and larch sawfly have major impacts on growth and stand dynamics of their respective host species. Global warming since the end of Little Ice Age around 1850 coincided with increasing precipitation and, hence, decreasing droughts in the southeastern boreal area of North America. The accelerated radial growth of eastern white-cedar and black ash at Lake Duparquet is a direct effect of these wetter climatic conditions. Population dynamics and forest composition, however, are rather indirectly affected by climate change through the alteration of the natural disturbance regimes, i. e., the decreased frequency and size of the forest fires and the increased frequency and amplitude of the spring floods. Potential consequences of future global warming on disturbance dynamics and forest composition are briefly discussed. The results of the dendroecological studies contributed to the elaboration of a natural-disturbance based forest management model for the southern boreal forest of Quebec.

Arboreal succession in the southern boreal forest of Quebec was documented through a dendroecological analysis of a mid-successional stand originating from fire 75 years ago. The studied stand was located in the forest surrounding Lake Duparquet, south of Lake Abitibi in northwestern Quebec. Tree composition and ecological characteristics were assessed in quadrats distributed systematically within the burnt area. One site was selected for a detailed dendroecological analysis as it was representative of the average composition found on moderately well-drained clay deposits. In a 20 m times 20 m quadrat, all living and dead tree stems ( gt 1 cm d.b.h.) were mapped and cut down. Cross sections collected at the root collar and at every metre were analyzed using standard dendrochronological techniques. While the prefire composition was characterized by an old ( gt 210 years) forest of Thuja occidentalis L. and Abies balsamea (L.) Mill., Populus tremuloides Michx and Betula papyrifera Marsh dominated the composition of the burnt area. These two species, originating most likely from suckering and sprouting, were recruited immediately after the fire while most of the Picea glauca (Moench) Voss and Abies regeneration was delayed for five years. Most Populus rapidly attained dominance while, with few exceptions, the other species were suppressed and occupied lower positions in the canopy. Differences in growth between Populus and Betula were accentuated by an important growth decrease in the mid-1950s, from which only Populus had fully recovered. Defoliation by the forest tent caterpillar caused hardwood growth decrease in the 1950s, as well as previous ones, while defoliation by the spruce budworm caused growth decreases and mortality in conifers around 1940 and from 1972 to 1987. Picea and Abies were regularly recruited since the fire and they formed an abundant understory cover. The recent recruitment of a few Thuja seedlings may be incidental or related to an increase in mosses with time since fire. Our results suggest that all species, except Thuja, can be abundant in the postfire cohort and that differences in diameter and height among species were explained by their respective growth and not by successive species invasion. This relatively regular stand development was, however, significantly influenced by episodes of insect defoliation. Mechanisms involved in subsequent stands development towards the mixed and coniferous compositions observed in older stands cannot be easily extrapolated from the present stand structure. Similar studies are therefore needed to explain these mechanisms in older stands.