by Audrey Verreault | 11 May 2020
Published in Journal of the Torrey Botanical Society 133(4): 519-527.
The genus Populus comprises some of the most commercially exploited, pioneer forest trees distributed throughout the northern-hemisphere. The high level of morphological diversity, extensive inter-species hybridization, and low level of DNA sequence variation among species in this group have impeded the progress of taxonomic and phylogenetic studies. We used nuclear genomic data based upon inter simple sequence repeat (ISSR) variability, a highly variable class of molecular markers to determine the genetic relationships among species of the genus Populus. Species of the section Populus (Leuce) clustered together suggesting monophyly of the section Populus. The Eurasian members of section Populus (P. alba, P. davidiana, and P. tremula) showed closer genetic relationships to each other than to two North American aspens (P. tremuloides and P. grandidentata) of the same section. In contrast to previous phylogenetic studies, P. nigra showed a close genetic relationship to species of the section Tacamahaca. This relationship is in agreement with various phenotypic traits, interfertility and chemistry of bud exudates and serves as evidence for introgression between P. nigra and species of the section Taccamahaca. Overall, the genetic relatedness estimates based on nuclear ISSR data were congruent with phylogenetic trees based on other molecular (RFLP and DNA sequence) and morphological data, but provided better resolution in assessing the genetic relatedness among closely related taxa, and provided genetic evidence for previously suspected introgressions.
by Audrey Verreault | 5 May 2020
Published in Canadian Journal of Forest Research 39: 264-284
A critical component of assessing the impacts of climate change on forest ecosystems involves understanding associated changes in the biogeochemical cycling of elements. Evidence from research on northeastern North American forests shows that direct effects of climate change will evoke changes in biogeochemical cycling by altering plant physiology, forest productivity, and soil physical, chemical, and biological processes. Indirect effects, largely mediated by changes in species composition, length of growing season, and hydrology, will also be important. The case study presented here uses the quantitative biogeochemical model PnET-BGC to test assumptions about the direct and indirect effects of climate change on a northern hardwood forest ecosystem. Modeling results indicate an overall increase in net primary production due to a longer growing season, an increase in NO3– leaching due to large increases in net mineralization and nitrification, and slight declines in mineral weathering due to a reduction in soil moisture. Future research should focus on uncertainties, including the effects of (1) multiple simultaneous interactions of stressors (e.g. climate change, ozone, acidic depositon); (2) long-term atmospheric CO2 enrichment on vegetation; (3) changes in forest species composition; (4) extreme climatic events and other disturbances (e.g., ice storms, fire, invasive species); and (5) feedback mechanisms that increase or decrease change.
by Audrey Verreault | 5 May 2020
Published in Forest Ecology and Management 258(12): 2683-2689
Due to the exceptional sweetness of its sap, sugar maple (Acer saccharum Marsh.) is economically exploited at a commercial scale for maple syrup production in northeastern North America. Approximately 80% of world production is realised in the province of Québec, Canada, where it is economically important for rural communities. Despite important financial investments in industrial infrastructure over recent decades, the maple syrup yield (ml of sap/tap/year) has followed a general declining trend over the last 15 years, presumably because of unfavourable climatic conditions. In this study, the relationship between climate and maple syrup yield by tap for the whole province was investigated.
A multiple regression model using four monthly climatic variables (mean January and April temperature and maximum temperature in February and March) explained 84% of the annual variation in yield between 1985 and 2006. This model was used to predict sugar maple syrup yield using a data set of future climatic scenarios issued from a large number of global climate models driven by different scenarios of CO2 emissions. The results show that sap yield of sugar maple should decrease by 15 and 22% in 2050 and 2090, respectively, as compared to the 1985–2006 period. The increase in mean April temperature was responsible for most of the reduction in yield. Assuming that the variables included in the prediction model are expressing a pattern of successive climatic conditions that could be displaced in time, i.e., that may happen sooner in the season, the maple syrup yield could be maintained at its current level if the period of sap production can shift in time to occur 12 days and 19 days sooner in 2050 and 2090, respectively. Other potential effects of climate change on sugar maple range and health that could also affect the yield of maple syrup production in the future were not addressed in this study.
by Marie-Claude Boileau | 29 April 2020
Published in European Journal of Forest Research 130: 117-133
Vegetation management is crucial to meeting the objectives of forest plantations. Following public hearing processes, chemical herbicides were banned on Crown forest lands in Québec (Canada) in 2001. Release now mainly relies on mechanical treatments. Our objectives are to review the historical context and the research conducted over the past 15 years that has led to the province’s current vegetation management strategy and to identify the major challenges of vegetation management being faced in Québec in the context of intensive silviculture and ecosystem-based management. Research has led to an integrated management model without herbicides, adapted to the ecological characteristics of reforestation sites. The Québec experience illustrates how, on most sites, vegetation management that is based on early reforestation, the use of tall planting stock and intensive mechanical release brings crop trees to the free-to-grow stage without the use of herbicides and without resulting in major effects on vegetation diversity. This vegetation management strategy is an asset in the implementation of ecosystem-based management. However, research demonstrates that mechanical release alone does not promote optimal crop-tree growth, due to rapid resprouting or suckering of competitors and competition from herbaceous species. Therefore, the current strategy poses important challenges in the management of plantations where the objective is to maximise wood production.
by Marie-Claude Boileau | 27 April 2020
Published in Forest Ecology and Management 278: 17-26
We applied four precommercial thinning (PCT) intensities (unthinned control, 2.5, 3.0, and 3.5 m residual spacings) to aspen (Populus tremuloides Michx.) stems, while preserving understory balsam fir (Abies balsamea (L.) Mill.) in an even-aged stratified boreal mixedwood stand. We evaluated treatment influence on aspen and balsam fir growth, and regeneration dynamics over a 10-year period. Compared to the unthinned control, PCT increased relative diameter increment of aspen saplings by 66–85% and relative basal area increment by 234–326%. Increases were similar among PCT treatments. Understory balsam fir regeneration ³ 1 m in height at time of thinning strongly benefited from PCT, with increases in height and crown width growth two to three times higher than in the control. The establishment of balsam fir regeneration, however, was not favored by PCT compared to the control. Our results show PCT increased tree size of individual aspen while promoting understory balsam fir growth in this type of stratified mixture. This approach should therefore be useful in limiting hardwood conversion in the boreal mixedwood forest at an early stage in stand development. Developing silvicultural approaches such as this one would be in line with the concept of ecosystem-based forest management.
