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.
by Audrey Verreault | 27 April 2020
Published in Journal of Environmental Quality 42: 623-639. doi: 10.2134/jeq2012.0378
Environmental change is monitored in North America through repeated measurements of weather, stream and river flow, air and water quality, and most recently, soil properties. Some skepticism remains, however, about whether repeated soil sampling can effectively distinguish between temporal and spatial variability, and efforts to document soil change in forest ecosystems through repeated measurements are largely nascent and uncoordinated. In eastern North America, repeated soil sampling has begun to provide valuable information on environmental problems such as air pollution. This review synthesizes the current state of the science to further the development and use of soil resampling as an integral method for recording and understanding environmental change in forested settings. The origins of soil resampling reach back to the 19th century in England and Russia. The concepts and methodologies involved in forest soil resampling are reviewed and evaluated through a discussion of how temporal and spatial variability can be addressed with a variety of sampling approaches. Key resampling studies demonstrate the type of results that can be obtained through differing approaches. Ongoing, large-scale issues such as recovery from acidification, long-term N deposition, C sequestration, effects of climate change, impacts from invasive species, and the increasing intensification of soil management all warrant the use of soil resampling as an essential tool for environmental monitoring and assessment. Furthermore, with better awareness of the value of soil resampling, studies can be designed with a long-term perspective so that information can be efficiently obtained well into the future to address problems that have not yet surfaced.
by Marie-Claude Boileau | 27 April 2020
Published in Soil Science Society of America Journal 78(S1): S196-S207. doi: 10.2136/ssaj2013.08.0373nafsc
While post-harvest residue (“slash”) is increasingly viewed as a source of biofuel, few studies have considered the potential ecological impact of the spatial distribution of forest harvest residue. We hypothesized that slash pilescreate islands of high soil fertility and light, leading to greater abundance, growth, and reproduction of plants. In 6-yr-old intensively managed hybrid poplar (Populus balsamifera L. ´ P. maximowiczii A. Henry) plantations, we showed that soluble organic N, NO3–N, NH4–N, and P decreased as a negative exponential function with distance from the pile. Pin cherry (Prunus pensylvanica L. f.) relative growth rate was fastest near piles in the first few years after harvest. We found significantly greater stem size, flowers per plant, and foliar P near piles for cherry, and this inverse gradient sharpened in a 16-yr-old white spruce [Picea glauca (Moench) Voss] plantation. For the two other flowering species, strawberry (Fragaria virginiana Mill.) and raspberry (Rubus idaeus L.), flower and fruit abundance were also significantly and strongly negatively correlated with distance to the pile. Further, directly correlating soil nutrient availability with plant traits, we found significant positive relationships between plant growth, reproductive output, and N availability. Partial correlation analysis indicated that more of the variance in plant traits was explained by distance than by soil nutrition. We conclude that in industrial forests, piles replace canopy gaps as sites where understory plant species can episodically reproduce and are therefore important for many plant species as well as the pollinators and frugivores dependent on them.
