by Marie-Claude Boileau | 28 July 2023
Published in Canadian Journal of Forest Research 00(2023) : 1-16. https://doi.org/10.1139/cjfr-2023-0062
Saplings (tree species whose diameter at breast height ranges from 1.1 to 9.0 cm) are important in forest growth and development. Their abundance and density can lead to specific forest successional trajectories and ecosystem characteristics. Yet, the consideration of saplings in forest management planning is a relatively new topic and is still rarely included in forest growth models. We developed sapling density models for 10 species groups with the objective of providing forest managers with additional tools to support the development of more precise prediction systems. We used dendrometric and environmental variables to model sapling density and species-wise density ratios. We evaluated Poisson and gamma regressions for the modelling of sapling density and zero-inflated logistic regressions to model species ratios. We used repeated measurements (from 1982 to 2019) from permanent sample plots located in hardwood forests in northeastern North America. Our results show that the gamma regression was superior to the Poisson regression. The cross-validated mean bias using gamma regression was 55 stems·ha−1 with a relative percentage error of 2.5% and an R2 of 0.43. The species-wise sapling density ratio model had an overall R2 of 0.93, and the species-wise mean R2 ranged between 0.90 and 0.96. Among the examined model covariates, stem density of merchantable-sized trees and latitude were significant in both models. We believe that the models we developed can be useful for forest management planning and sustainable merchantable production.
by Marie-Claude Boileau | 28 July 2023
Published in Forestry 2023(cpad029). https://doi.org/10.1093/forestry/cpad029
Tree recruitment is affected by numerous biotic and abiotic factors, including climate. However, the relative importance of climate variables in empirical models of tree recruitment remains to be evaluated. We fitted models of tree recruitment to 26 species in the province of Quebec, Canada. For a better understanding of the recruitment process, we used a two-part model to distinguish recruitment occurrence from abundance. The relative importance of the different variables was assessed using Akaike weights. Our main hypothesis was that climate is one of the major drivers of tree recruitment. Our results showed that growing degree-days counted among the major drivers of recruitment occurrence but not of recruitment abundance. Stand variables, such as the presence and abundance of adult trees of the species, and broadleaved and coniferous basal areas were found to be relatively more important than all the climate variables for both recruitment occurrence and abundance. Species occupancy within a 10-km radius also had a significant effect on recruitment occurrence for two-thirds of the species, but it was less important than growing degree-days and other stand variables. Climate change is expected to improve the suitability of habitats located at the northern edge of species distributions. However, our model predictions point to a low probability of colonization in newly suitable habitats in the short term.
by Marie-Claude Boileau | 25 July 2023
Published in Forests 14(6): 1124. https://doi.org/10.3390/f14061124
The soil microbiome plays major roles in the below-ground processes and productivity of forest ecosystems. Atmospheric nitrogen (N) deposition is predicted to increase globally and might create disturbances in soil microbial communities, essentially by modifying soil chemistry. However, the impacts of higher N deposition on the soil microbiome in N-limited northern forests are still unclear. For 16 years, we simulated N deposition by adding ammonium nitrate at rates of 3 and 10 times the ambient N deposition directly into soils located in three bioclimatic domains of the eastern Canadian forest (i.e., sugar maple–yellow birch, balsam fir–white birch, and black spruce–feather moss). We identified changes in the microbial communities by isolating the DNA of the L, F, and H soil horizons, as well as by sequencing amplicons of the bacterial 16S rRNA gene and the fungal ITS region. We found that long-term increased N deposition had no effect on soil microbial diversity, but had moderate impacts on the composition of the bacterial and fungal communities. The most noticeable change was the increase in ectomycorrhizal fungi ASV abundance, potentially due to increased tree root growth on fertilized plots. Our work suggests that, in N-limited northern forests, extra N is rapidly mobilized by vegetation, thus minimizing impacts on the soil microbiome.
by Marie-Claude Boileau | 24 July 2023
https://doi.org/10.2737/NRS-GTR-P-211-paper39
Improving financial revenues from partial cuts in sugar maple (Acer saccharum) stands at the northern edge of the species’ range involves harvesting trees that have reached their financial maturity size (i.e., the diameter at which their monetary value is greatest and beyond which there is no further gain). To establish the lumber value of each tree at the sawmill, a sample of 171 trees were measured, felled, bucked into logs, and sawn into boards. We estimated their value changes over 10 years using data from a network of permanent sample plots. The most vigorous and best quality maples started losing value at a diameter at breast height of 36 cm. Those belonging to the lowest grade and containing a potential sawlog increased in value, but only marginally. The low value of these trees makes the profitability of forest management challenging at the northern edge of sugar maple’s range.
by Marie-Claude Boileau | 24 July 2023
https://doi.org/10.2737/NRS-GTR-P-211-paper18
Yellow birch (Betula alleghaniensis Britt.) is the second most harvested hardwood species in Quebec. Hardwood stands harboring this species are likely to yield high value products, and their proximity to inhabited regions facilitates a more intensive silviculture. Yet, little is known about the effects of silvicultural treatments such as commercial thinning on stands composed mostly of yellow birch. We set up an experiment in a 41-year-old yellow birch stand that arose after a clearcutting in 1971. The experimental design comprises four treatments: a control (no intervention); and light, moderate, and heavy commercial thinnings. After 5 years, results show that the thinnings had no significant effect on the net growth in basal areal of the stand. The treatments mostly led to an increase in the proportion of yellow birch and crop trees in the stand following the harvest targeting aspens and other less desired species. The smaller diameter trees near the trails showed the highest diameter growth response to the thinnings.
