by Claire Morin | 8 October 2020
Published in Frontiers in Ecology and Evolution 8: 257. https://doi.org/10.3389/fevo.2020.00257
Human activities have changed forest composition of northeastern North America since European settlement by increasing the importance of pioneer shade-intolerant species, at the expense of shade-tolerant and long-lived species. This study used tree taxa lists from land survey archives (1842–1935) to document the pre-settlement forest composition in a heavily transformed region at the temperate-boreal interface in eastern Québec (Canada). Pre-settlement forests were dominated by a spruce-fir-white birch assemblage. Two additional assemblages were characterized by high relative frequency of the fire-adapted jack pine and poplar, suggesting that fire was an important factor of pre-settlement forest dynamics. Comparison with modern forest inventories (1980–2010) showed that trembling aspen, jack pine and red maple increased to the detriment of spruce, yellow birch, and white and red pines. The spruce-fir-white birch assemblage is now confined to high elevations and steep slopes, while the jack pine assemblage has extended its distribution and strengthen its association with sandy deposits. Surveyors’ fire observations revealed a high fire activity during the settlement period (1842–1971) and human ignitions were probably the predominant cause. While settlement fires are a likely explanation for the post-settlement increase of jack pine and trembling aspen, industrial logging and land clearing are important factors that could explain the decline of spruce and pines (red and white). Ecosystem-based forest management should aim to increase spruce frequency and dominance over disturbance-adapted (shade intolerant and fast-growing) species, and to restore yellow birch, cedar, white, and red pines in the plains sector where forest transformation has been the most important.Human activities have changed forest composition of northeastern North America since European settlement by increasing the importance of pioneer shade-intolerant species, at the expense of shade-tolerant and long-lived species. This study used tree taxa lists from land survey archives (1842–1935) to document the pre-settlement forest composition in a heavily transformed region at the temperate-boreal interface in eastern Québec (Canada). Pre-settlement forests were dominated by a spruce-fir-white birch assemblage. Two additional assemblages were characterized by high relative frequency of the fire-adapted jack pine and poplar, suggesting that fire was an important factor of pre-settlement forest dynamics. Comparison with modern forest inventories (1980–2010) showed that trembling aspen, jack pine and red maple increased to the detriment of spruce, yellow birch, and white and red pines. The spruce-fir-white birch assemblage is now confined to high elevations and steep slopes, while the jack pine assemblage has extended its distribution and strengthen its association with sandy deposits. Surveyors’ fire observations revealed a high fire activity during the settlement period (1842–1971) and human ignitions were probably the predominant cause. While settlement fires are a likely explanation for the post-settlement increase of jack pine and trembling aspen, industrial logging and land clearing are important factors that could explain the decline of spruce and pines (red and white). Ecosystem-based forest management should aim to increase spruce frequency and dominance over disturbance-adapted (shade intolerant and fast-growing) species, and to restore yellow birch, cedar, white, and red pines in the plains sector where forest transformation has been the most important.
by Claire Morin | 8 October 2020
Published in Tree Planters’ Notes 63(1): 51-60
A strong differentiation of bud set among natural populations may lead to limited adaptive capacity of seed sources during assisted population migration. The present study aimed to fill gaps regarding the dynamic nature of bud set and its variation among genetically improved white spruce (Picea glauca [Moench] Voss) seed sources used in the reforestation program in Québec, Canada. Bud set phases of seedlings from eight white spruce seed sources were monitored during the first growing season on a test plantation site. Results showed that bud set phases were interdependent but did not vary significantly among seed sources. Bud set timing was unrelated to the latitude or longitude of geographic origin. The lack of significance in bud set timing among tested seed sources may indicate low potential risk associated with the transfer of southern seed sources to the northern locations.
by Marie-Claude Boileau | 8 October 2020
Published in Microorganisms 8(7): 1088. https://doi.org/doi:10.3390/microorganisms8071088
The acidity of peat-based substrates used in forest nurseries limits seedling mineral nutrition and growth as well as the activity of microorganisms. To our knowledge, no study has yet evaluated the use of granular calcite as a covering material to increase pH, calcium and CO2 concentrations in the rhizosphere and ectomycorrhizal development. The objective is to compare different covering treatments on early colonization of the roots by ectomycorrhizal fungi, as well as the growth and calcium nutrition of white spruce seedlings in the forest nursery. Three treatments were used to cover the plant cavities (Silica (29 g/cavity; control treatment), Calcite (24 g/cavity) and calcite+ (31 g/cavity)) and were distributed randomly inside each of the five complete blocks of the experimental design. The results show that calcite stimulates natural mycorrhization. Seedlings grown with calcite have significant gains for several growth and physiological variables, and that the periphery of their root plugs are more colonized by the extramatrical phase of ectomycorrhizal fungi, thus improving root-plug cohesion. The authors discuss the operational scope of the results in relation to the tolerance of seedlings to environmental stress and the improvement of their quality, both in the nursery and in reforestation sites.
by André Boily | 8 October 2020
Published in Tree Physiology, tpaa096. https://doi.org/10.1093/treephys/tpaa096
Late frost can cause damage to trees, especially to the developing bud of broadleaf species in spring. Through long-term adaptation, plants adjust leaf phenology to achieve an optimal trade-off between growing season length and frost avoidance. In this study, we aim to assess ecotypic differentiation in leaf development of sugar maple populations planted in a common garden. A total of 272 sugar maple seedlings from 29 Canadian provenances were planted at the northern boundary of the natural range and the phenological phases of bud and leaf development were monitored during spring 2019. The wide geographical area under evaluation showed a complex seasonal pattern of temperature, with spring warming occurring later in the north and close to the sea. Overall, leaf development lasted between 20 and 36 days, from the end of May to end of June. We observed different timings and rates of leaf development among provenances, demonstrating the occurrence of ecotypes in this species. Minimum April temperatures of the original sites were able to explain such differences, while maximum April temperatures were not significant. Seedlings from sites with colder minimum April temperatures completed leaf development earlier and faster. On average, leaf development diverged by up to 6 days among provenances with minimum April temperatures ranging from −3 to 3°C. Our results demonstrated that the avoidance of late spring frost is a driving force of leaf development in sugar maple populations. In the colder sites, the growing season is a limiting factor for tree growth. Thus, when thermal conditions become favorable in spring, an earlier growth reactivation and high metabolic activity ensure a fast leaf emission, which maximizes the period available for photosynthesis and growth. These patterns demonstrate the long-term phenological adaptation of sugar maple populations to local climatic conditions and suggest the importance of frost events for leaf development.
by Marie-Claude Boileau | 8 October 2020
Published in Forest Ecology and Management 466: 118115. https://doi.org/10.1016/j.foreco.2020.118115
The success of partial cut applications to northern hardwood stands is based upon the contribution of harvested and residual trees to overall stand growth, which can be captured by a stand-level criterion, i.e, the growth dominance coefficient (GDC). The main objective of this study was to test the relevance of GDC in evaluating the success of partial cuts in even-aged and uneven-aged stands that were composed of sugar maple (Acer saccharum Marsh.) and yellow birch (Betula alleghaniensis Britt.). We first determined whether GDC that was calculated with two indicators of light capture, stem mass and tree leaf area, produced similar results after partial cutting in both stand structures. Second, using linear mixed models, we determined the effect of selection cutting on GDC in uneven-aged stands over the short- and medium-term, and evaluated effects of tree vigour and size before cutting on diameter growth response of trees after cutting. GDC based upon stem mass was similar to GDC based upon tree leaf area in even-aged stands (p = 0.7200), but was lower in uneven-aged stands (p < 0.001). Selection cutting in uneven-aged stands did not change GDC in the short- (p = 0.7721) and medium- (p = 0.8363) term. Yet, several trees that grew rapidly before cutting responded negatively to partial cutting, while many trees that grew slowly before cutting responded positively. Overall, assessing the success of partial cuts appears to be difficult using GDC, a stand-level criterion. Such assessments, as well as a better understanding of the effects of partial cuts, could be obtained through more detailed growth analyses that are performed at the tree level.
