Fire is a dominant mechanism of forest renewal in most of Canada’s forests and its activity is predicted to increase over the coming decades. Individual fire events have been considered to be non-selective with regards to forest properties, but evidence now suggests otherwise. Our objective was therefore to quantify the effect of forest properties on fire selectivity or avoidance, evaluate the stability of these effects across varying burn rates, and use these results to map local fire risk across the forests of Canada. We used Canada-wide MODIS-based maps of annual fires and of forest properties to identify burned and unburned pixels for the 2002–2011 period and to bin them into classes of forest composition (% conifer and broadleaved deciduous), above-ground tree biomass and stand age. Logistic binomial regressions were then used to quantify fire selectivity by forest properties classes and by zones of homogeneous fire regime (HFR). Results suggest that fire exhibits a strong selectivity for conifer stands, but an even stronger avoidance of broadleaved stands. In terms of age classes, fire also shows a strong avoidance for young (0 to 29 year) stands. The large differences among regional burn rates do not significantly alter the overall preference and avoidance ratings. Finally, we combined these results on relative burn preference with regional burn rates to map local fire risks across Canada.

A recent global study reported a net difference between areas of forest cover loss and of forest cover gain of about 3.6% of total forest area across the boreal biome, and of 5.6% for Canada, over a 12‐yr period. Net losses of this magnitude should be of concern given the importance of this biome in global biogeochemical cycles linked to climate change. Our analysis for Canada fails to support these results and suggests that post‐harvest recovery of tree cover is generally strong, while post‐fire recovery of tree cover is weaker but nevertheless prevalent. We find that current large area remote sensing methodologies can fail to properly recognize post‐disturbance recovery from non‐forest to forest status in low‐productivity boreal forests when using short time series. With climate change and human impacts intensifying around the world, it is urgently important to be able to reliably distinguish temporary forest cover loss followed by naturally slow recovery from forest decline requiring policy action. The analysis was in large part based on the new Canada Landsat Disturbance product in which fires and harvest since 1984 are mapped at 30‐m resolution (https://doi.org/10.23687/add1346b-f632-4eb9-a83d-a662b38655ad).

We have adjusted two growth and yield models to temporary sample plots from across Canada, and used climate variables in lieu of phytometric indices such as site index to represent, in part, the site-level variability in growth potential. Comparison of predicted increments in plot-level height, basal area and merchantable wood volume to increments of these variables measured in permanent sample plots shows a moderate to poor predictive ability. Comparison with the performance of four operational growth and yield models from different provinces across Canada shows comparable predictive power of this new model versus that of the provincial models. Based on these results, we suggest that the simplification of regional growth and yield models may be achieved without further loss of predictive power, and that the large error in the prediction of growth increment is mostly associated with the use of temporary sample plots which, by definition, contain little information on stand dynamics. We also suggest that, because of the empirical nature of these growth and yield models, the scale of application should determine the appropriate scale of the model. National estimates of forest growth are therefore less likely to be biased if obtained from a national model only than if obtained from a combination of regional models, where those exist, gap-filled with estimates from a national model. Key words: yield model, merchantable wood volume, stand age, climatic variables, simultaneous regression, robust regression

Measuring net primary productivity of trees requires the measurement of total wood production of branches. Recent work on balsam fir ( Abies balsamea ) has shown that branch-wood production can be estimated as a function of foliage production. We extend the analysis to four other species found in the Canadian forest: black spruce ( Picea mariana ), jack pine ( Pinus banksiana ), Douglas-fir ( Pseudotsuga menziesii ), and trembling aspen ( Populus tremuloides ). Results show that the ratio of annual branch-wood production to annual foliage production is about 1.0 for conifer species (between 0.86 and 1.12) and 0.56 for aspen during a nondrought year. An analysis using field measurements of litterfall and stem-diameter increment from selected forested sites shows that branch-wood production accounts for a smaller proportion of aboveground net primary productivity in trembling aspen (15%–20%) than in conifer species (25%). Also, litterfall capture of small branches (<1 cm diameter) accounts for only 33% of branch detritus production in conifers and 50% in trembling aspen. This study supports the use of an alternative method for estimating branch-wood production that reduces the potential bias in field estimates of net primary productivity.

In production tunnels, time domain reflectometry (TDR) was used to manage irrigation and leaching by con- trolling water content in the rhizosphere of air-slit containerized white spruce ( Picea glauca (Moench) Voss) seedlings (1+0). Seedlings were exposed to four irrigation regimes (v/v: IR-60%, IR-45%, IR-30%, and IR-15%) during the first growing season to assess IR effects on growth, gas exchange, nutrient uptake, carbohydrates, root architecture, and leaching. In the province of Quebec, seedling producers generally maintain a high substrate water content (>50%, v/v) during all growth phases. The accuracy and feasibility of using TDR to decrease irrigation without affecting the mate - rial attributes of the seedlings at the end of the first growing season was confirmed. However, seedlings grown under IR-15% had significantly lower height, root collar diameter, shoot and root dry masses, root surface, root length, net photosynthesis, and nutrient contents than seedlings grown under IR-30%, IR-45%, and IR-60%. In comparison with IR-30% and IR-45%, the application of IR-60% produced no increase in shoot or root growth, mineral nutrition, and carbohydrates. Seedlings grown under IR-15%, IR-30%, and IR-45% used approximately 28, 37, and 46%, respectively, of the amount of water applied under IR-60%. Nutrient losses including anions and cations under IR-60% were higher in comparison with the other IRs. Maintaining a water content in the rhizosphere that changes with the stage of seed- ling development is suggested to optimize growth and to avoid excess irrigation and leaching.