Ontario Forest Research Institute,Ministry of Natural Resources and Forestry,Government of Canada

Black spruce breeding zones (BZs) in northwestern Ontario, Canada, were assessed for the feasibilities of expanding superior tree selection and orchard seed deployment across existing BZ boundaries under climate change. The assessment was based on performances of open-pollinated families in progeny tests established in four second-generation BZs. In these tests, families from outside BZs were tested alongside with families from within BZs. Results showed that trees grew faster with higher survival rates in southerly BZs than in northerly BZs. Within a BZ, families from southern BZs were taller, but with slightly lower survival rates in northerly BZs, while families from northern BZs were shorter with comparable survival in southern BZs. These patterns were consistent with results from provenance studies, suggesting potential benefits from deploying orchard seeds from southern BZs more northwardly, provided slightly lower survival rates not serious concerns. Genetic worth of breeding populations for the next generation could be improved by 4.6% in height when the top 100 genetically superior trees were selected with families within BZs. Allowing selection to include families from southerly BZs could lead to an average improvement of 4.9%. The implications for black spruce tree improvement programs are discussed.

The objective of this research was to understand how the long-term climate warming effect of harvested wood products (HWP) changed as the proportional distribution of disposed products across three primary pathways (incineration, recycling, and landfilling) varied while accounting for the possibility of multiple recycling steps. The climate warming effect is defined as greenhouse gas (GHG) emissions from the disposal of carbon content in HWP, not including emissions from processing the disposed HWP and substitution effects. Emissions were estimated over 100 years from the year of the original HWP disposal. For solid HWP, the climate warming effect decreased, for any given recycling fraction, as the landfill fraction decreased. The opposite, however, occurred for paper HWP. Recycling reduced the climate warming effect of solid HWP by “pushing” some of the emissions outside of the assessment period. For paper HWP, recycling did not change the climate warming effect unless the assessment period was relatively short. These findings can be used to assess the effect of a given combination of disposal fates of HWP, including the final disposal of non-recyclable HWP, and indicate whether it exceeds the effect of instantaneously releasing the HWP carbon content as CO2.

Abstract Ecological forestry rooted in natural disturbance‐based silviculture (NDBS) aims to help maintain or facilitate recovery of ecosystem structure and function toward conditions found in unharvested stands. In the short term, leaving a portion of a stand's merchantable trees intact at harvest should increase similarity in composition and function relative to stands following non‐stand‐replacing natural disturbances such as low‐intensity fires, windthrow, or insect outbreaks and thus maintain biodiversity and other ecosystem services. Testing NDBS requires long‐term data, while assessing the generality of responses to NDBS requires such data from multiple experiments across diverse stand and site conditions. To date, our understanding of forest responses to NDBS has been limited by a lack of opportunities to explore responses across time. In this study, we utilized data from three long‐term experiments encompassing 21 combinations of harvest treatments by stand type plus unharvested reference stands. These experiments provide data to assess responses for 12 to 20 years post‐treatment. We quantified the direction (increasing or decreasing), duration (persisting or transient), magnitude, and temporal dynamics of responses in stand‐level tree growth, mortality, and regeneration abundances. High‐intensity treatments (≥40%) produced strong initial impacts, particularly increased tree mortality (although not statistically significant across all treatments), which in turn had prolonged effects on stand‐level growth through reduced tree density. These treatments also promoted increased broadleaf regeneration, likely due to greater canopy opening and enhanced light availability. We observed an inconsistent stand‐level growth response to treatments, with some treatments showing initial decline while others eventually resulted in higher growth in harvested stands. In mixed stands, coniferous species showed growth benefits when coexisting with broadleaf species, possibly due to reduced intraspecific competition or improved access to resources mediated by broadleaf neighbours. This growth advantage was not observed for broadleaf species, indicating asymmetric benefits in mixed stands. Response patterns and magnitude vary over time and are influenced by local factors such as stand type, overstory retention, species, and initial treatment impact. This variability highlights the potential for tailoring NDBS approaches locally to achieve desired outcomes and underscores the need to incorporate stand‐specific conditions into ecological forestry practices.

We used the forest carbon budget model FORCARB-ON2 to project carbon stocks in a forest ecosystem and harvested wood products (HWP) in the six ecoregions of Ontario’s managed forests. Carbon stock levels were predicted from 2021–2100 for three management scenarios with a constant harvesting level throughout the simulation horizon and for two natural development scenarios. Harvesting levels in three management scenarios reflected actual harvest volumes from 2011–2020 and 2001–2020 and planned harvest volumes (i.e., maximum harvest volume allowed in forest management plans) from 2011–2020. Natural development scenarios assumed no harvesting and either pre-suppression era or modern natural disturbance cycles. The results indicate that keeping harvest volumes at the historical levels (either 2011– 2020 or 2001–2020) would increase carbon stocks in forests and HWP by the end of the century. However, increasing harvesting to the maximum planned level would reduce stocks in both forest and combined forest–HWP pools. The analyzed management scenarios suggest there is room to increase harvest volumes to a level between historical and maximum planned, while maintaining various carbon stock indicators at 2021 levels. The results assume that forest growth, successional changes, and natural disturbance remain constant throughout this century. Changes to the above rates caused by climate change or widespread natural disturbances would affect future forest conditions and may alter predicted forest carbon stocks.

Soil protists play crucial roles in nutrient cycling, organic matter decomposition, and regulating belowground food webs, but relatively little is known about the effects of tree diversity on this microscopic group. We used the International Diversity Experiment Network with Trees (IDENT) experiment in Sault Ste. Marie, Canada to address the effects of tree species richness and functional diversity, and high and low growing season soil moisture treatments on soil ciliate abundance. In total, we found 2285 ciliates from 181 plots representing 22 tree communities and an unplanted control plot. Soil ciliate abundance varied significantly with species identity of tree communities, but no significant non-additive net mixing effects was found. Ciliate abundance was also significantly and negatively influenced by soil temperature on the day of sampling. We found a significant, albeit weak, positive relationship between tree species richness and total ciliate abundance that was driven primarily by Paramecium spp. Functional tree diversity had a similar relationship with ciliate abundance that was only marginally significant, while soil moisture treatment had no effect on abundance. These findings suggest that higher tree species richness in young plantations can have a positive influence on the abundance of soil ciliates, though the relationship is context-dependent, differing slightly with species identity of trees. Our study contributes to our current knowledge of tree diversity effects on soil ciliate abundance and highlights the need for further research to fully understand these complex relationships and their implications for forest ecosystem functioning.