by Marie-Claude Boileau | 7 November 2022
Published in Ecosystems, 21: 1183-1195. https://link.springer.com/article/10.1007/s10021-017-0211-3
Balsam fir (Abies balsamea) and black spruce (Picea mariana) forests are the main conifer forest types in the North American boreal zone. The coexistence of the two species as well as their respective canopy dominance in distinct stands raises questions about the long-term evolution from one forest type to the other in relation to environmental factors including climate and stand disturbance. We tested the hypothesis that repetitive fire events promote the succession of balsam fir forests to black spruce forests and vice versa. Post-fire chronosequences of one black spruce (BSP) and one balsam fir (BFI) site were reconstructed based on the botanical composition and ¹⁴C-dated soil macro-charcoals. The results support the hypothesis of successional dynamics. The BSP site has been affected by fire for the past 7600 years, whereas the BFI site, after having been affected by several fires during the first-half of the Holocene, evolved in a fire-free environment for the last 4400 years. Periods of fire activity facilitated the dominance of black spruce forests. The cessation of fires around 4400 cal. years BP on the BFI site marks the beginning of the transition from black spruce to balsam fir stands. This succession is a long process, due to the ability of black spruce to regenerate by layering in the absence of fire. The resulting balsam fir stands are ancient and precarious ecosystems, since fire generally leads to the return of black spruce. The increase in balsam fir to the detriment of black spruce in boreal forests is a response to a decrease in fire frequency.
by Marie-Claude Boileau | 7 November 2022
Published in Remote Sensing, vol 11(7), p. 863.
Underestimation of LiDAR heights, which is linked to the pulse’s probability of reaching the top of vegetation and the ground, is widely known but has never been evaluated for different sensors and for diverse types of ecological conditions. The main causes for this underestimation are: pulse density, scan pattern (sensors), scan angles, and specific contract parameters (flight altitude, pulse repetition frequency), together with territory characteristics (slope, stand density, species composition). This study, which was conducted at a 1 × 1 m resolution, calculated the bias of both the digital terrain model (DTM) and canopy height model (CHM) by subtracting two LiDAR datasets: high-density pixels with 21 pulses/m² (first return) and more (DTM or CHM reference value pixels); and low-density pixels (DTM or CHM value to correct). After preliminary analyses, we concluded that the DTM did not need any specific adjustment; only CHM needed it. Among the variables studied, three were selected for the final CHM adjustment model and an empirical equation using a non-linear mixed model was developed. CHM underestimation correction could be applied before using the CHM for volume calculations, in forest growth models or for multi-temporal analysis.
by Marie-Claude Boileau | 7 November 2022
Published in The Forestry Chronicle, vol. 97(2), 109-126
The Canadian forest sector requires detailed information regarding the amount and characteristics of the forest resource. To address these needs, inventory systems that spatially quantify timber and other forest related ecosystem services are required, and which are accurate, comprehensive and timely. The Assessment of Wood properties using Remote Sensing (AWARE) was a five-year project involving collaboration between seven Canadian universities and seven forest companies, with support provided by provincial and federal forestry agencies and other not-for-profit forestry focused organizations. AWARE provided methods and tools to enhance the characterization of forests at national, landscape and individual tree-scales. The project supported 24 post-doctoral fellows, as well as PhD and MSc students who examined the roles that advanced three-dimensional remote sensing technologies can play in the development of accurate forest inventory systems across Canada. In this review, we examine the AWARE research project, review research highlights, key outcomes, future research needs, and provide an assessment of successes and challenges the project faced over its five-year lifespan.
by Audrey Verreault | 3 November 2022
Published in Forests 13(11): 1832. https://doi.org/10.3390/f13111832
In boreal forests in Canada, broadleaf stands are characterized by generally well-drained soils and a humus-rich layer. In contrast, spruce-moss stands are often characterized by more poorly drained soils and acidic humus layer. However, presence of these two forest types in various degrees of mixture in stands can be beneficial to spruce seedlings productivity. It was hypothesized that leaf litter and humus from pure spruces-moss stands, pure broadleaf stands, and mixed stand may influence Black spruce (Picea mariana (Mill.) BSP) seedling growth and development differently. A greenhouse experiment was carried out to evaluate the effect of different leaf litter and different humus on spruces seedlings. Our results suggest better development for seedlings grown in humus from mixed stands and pure broadleaf stands compared to humus from pure B. spruce or standard forest nursery substrate. Furthermore, leaf litter from broadleaf trees species, such as species Speckle alder (Alnus rugosa (Du Roi) R.T. Clausen), T. aspen (Populus tremuloides Michx),Willows (Salix spp.) and Paper birch (Betula papyrifera Marsh.), has shown distinct results in the growth and development of B. spruce seedlings in greenhouse. Furthermore, promotion of mixed stand can increase B. spruce productivity by improving the physicochemical composition of the forest floor.
by Svetlana Savin | 2 November 2022
Published in Canadian Journal of Forest Research 52(11): 1412-1422. https://doi.org/10.1139/cjfr-2022-0072
Eastern white cedar (Thuja occidentalis) and red spruce (Picea rubens) contribute to the biodiversity and resilience of mixedwood forests. However, cuts that remove most or all the forest cover can cause the decline of these species. Among partial cutting options, the irregular shelterwood system (ISS) can create successful conditions for the development of advance regeneration and enrichment planting. We studied 6 years of ecophysiology of lower advance regeneration and planted seedlings of eastern white cedar and red spruce growing under a first ISS cut according to three cutting intensities: light cut (35% removal, 20 m2·ha−1 residual basal area), moderate cut (42%, 18 m2·ha−1), and heavy cut (52%, 15 m2·ha−1). Light-saturated photosynthesis and height growth of planted cedar and both spruce types decreased with increasing cutting intensity, in response to an increase in competing vegetation. Therefore, to limit the negative impact of competing species on cedar and spruce regeneration, we recommend protecting tall advance regeneration (2 m+) during partial cut operations and using large-sized containerized seedlings (40–50 cm height) for enrichment planting. Results also suggest that a mechanical release could help optimize the physio-morphology and growth of both regeneration types of cedar and red spruce.
