by Claire Morin | 8 October 2020
Published in Forest Ecology and Management 466: 118137. https://doi.org/10.1016/j.foreco.2020.118137
In northeastern North America, mixed hardwood-conifer forests have commonly been harvested with selective practices such as diameter-limit cutting. By removing trees of highest commercial value, these cuts often left stands with highly variable density and reduced volume, less species diversity, and lower wood quality. The lack of care to the regenerating layer also resulted in regeneration deficiencies, especially on productive sites supporting yellow birch (Betula alleghaniensis Britton)-conifer stands. We assessed the 15-yr effects of four rehabilitation scenarios on stand growth, quality, vigor and regeneration in an experiment established in Quebec, Canada. The trial compared untreated experimental units (e.g. control), uniform shelterwood method (50 overstory trees/ha), strip clearcutting (20-m strips), and seed-tree method (10 overstory trees/ha), all combined with 3 site preparation treatments (no scarification, mechanical raking, and spot scarification). After 15 years, the ongoing recovery of growth, vigor and regeneration in the control and untreated part of the strip clearcut plot reflected the resilient nature of these mixedwood stands, with conifer (Abies balsamea [L.] Mill., Picea rubens Sarg., Picea glauca [Moench] Voss) saplings and poles contributing to the recovery of total BA and that of vigorous trees (i.e. acceptable growing stock [AGS]). The control and strip clearcut treatments, however, had high BA of unacceptable growing stock. Shelterwood plots recovered more slowly in BA and AGS, but had greater BA of high-quality trees than the control. Seed-tree method was less optimal because of its slow recovery and high understory competition. The lack of synchronization with a good seed year limited the efficiency of scarification, and increased the abundance of non-commercial species. An active rehabilitation strategy combining shelterwood system and ground disturbance (e.g. raking) during a good seed year should help to improve stand quality and regeneration. Yet, our results indicate that retaining conifers in the understory and overstory would ensure a seed source and accelerate recovery. Where seed sources and conifer advance regeneration are lacking, enrichment planting may be necessary to maintain a mixedwood composition over time.
by Claire Morin | 8 October 2020
Published in Global Change Biology 26(4): 2072-2080. https://doi.org/10.1111/gcb.14991
Abstract Climate change is altering phenology; however, the magnitude of this change varies among taxa. Compared with phenological mismatch between plants and herbivores, synchronization due to climate has been less explored, despite its potential implications for trophic interactions. The earlier budburst induced by defoliation is a phenological strategy for plants against herbivores. Here, we tested whether warming can counteract defoliation-induced mismatch by increasing herbivore-plant phenological synchrony. We compared the larval phenology of spruce budworm and budburst in balsam fir, black spruce, and white spruce saplings subjected to defoliation in a controlled environment at temperatures of 12, 17, and 22°C. Budburst in defoliated saplings occurred 6–24 days earlier than in the controls, thus mismatching needle development from larval feeding. This mismatch decreased to only 3–7 days, however, when temperatures warmed by 5 and 10°C, leading to a resynchronization of the host with spruce budworm larvae. The increasing synchrony under warming counteracts the defoliation-induced mismatch, disrupting trophic interactions and energy flow between forest ecosystem and insect populations. Our results suggest that the predicted warming may improve food quality and provide better growth conditions for larval development, thus promoting longer or more intense insect outbreaks in the future.
by Marie-Claude Boileau | 8 October 2020
Published in Annals of Forest Science 77(2): 38. https://doi.org/10.1007/s13595-020-0929-5
A model describing species composition, density and diameter distribution of saplings was developed from operational inventory data. It could be used as an input into growth models calibrated exclusively with merchantable trees to correct some recruitment bias. Important differences in distributions were found between plantations and naturally regenerated stands. Longer-term monitoring would be required to observe the effects of thinning treatments on saplings.
by Claire Morin | 8 October 2020
Published in Frontiers in Plant Science 10: 1276. https://doi.org/10.3389/fpls.2019.01276
Climate change is steering tree breeding programs towards the development of families and genotypes that will be adapted and more resilient to changing environments. Making genotype–phenotype–environment connections is central to these predictions and it requires the evaluation of functional traits such as photosynthetic rates that can be linked to environmental variables. However, the ability to rapidly measure photosynthetic parameters has always been limiting. The estimation of Vc,max and Jmax using CO2 response curves has traditionally been time consuming, taking anywhere from 30 min to more than an hour, thereby drastically limiting the number of trees that can be assessed per day. Technological advancements have led to the development of a new generation of portable photosynthesis measurement systems offering greater chamber environmental control and automated sampling and, as a result, the proposal of a new, faster, method (RACiR) for measuring Vc,max and Jmax. This method was developed using poplar trees and involves measuring photosynthetic responses to CO2 over a range of CO2 concentrations changing at a constant rate. The goal of the present study was to adapt the RACiR method for use on conifers whose measurement usually requires much larger leaf chambers. We demonstrate that the RACiR method can be used to estimate Vc,max and Jmax in conifers and provide recommendations to enhance the method. The use our method in conifers will substantially reduce measurement time, thus greatly improving genotype evaluation and selection capabilities based on photosynthetic traits. This study led to the developpement of an R package (RapidACi, https://github.com/ManuelLamothe/RapidACi) that facilitates the correction of multiple RACiR files and the post-measurement correction of leaf areas.
by Marie-Claude Boileau | 7 October 2020
Natural Resources Canada, Canadian Forest Service. Information Report GLC-X-23. 156 p.
The Canadian National Vegetation Classification (CNVC) is an ecological classification of natural vegetation communities in Canada. Using eight hierarchical levels, it provides a nationally standardized framework for describing vegetation patterns within their ecological contexts at multiple conceptual and spatial scales. Natural Resources Canada, Canadian Forest Service (NRCan – CFS) has led the development of the CNVC since it began in 2000, working primarily on forest and woodland communities, and mainly at two levels of the hierarchy, the mid-level Macrogroup and the stand-level Association. CNVC development relies on partnerships with provincial and territorial government agencies for regional ecological expertise and data, and benefits from international collaborations for comparisons with other national classifications. This report introduces the CNVC, including its rationale, history and partnerships; presents the classification framework (hierarchy); documents methods employed to 2018 for the development of types, including information sources and the bioregional expert review process; and describes the products to date, available on the CNVC website and the Natural Resources Canada – Canadian Forest Service Publications website. Developing and maintaining a national classification framework requires considerable resources, and ongoing funding is needed to sustain the effort summarized here.
