by Claire Morin | 30 January 2019
Published in Biogeosciences 10: 4627-4639 https://doi.org/5194/bg-10-4627-2013
Nitrogen (N) is a major growth-limiting factor in boreal forest ecosystems. Increases of temperature and atmospheric N deposition are expected to affect forest growth directly and indirectly by increasing N availability due to higher rates of N mineralization. In order to understand the potential impacts of these changes, a mature balsam fir stand in Québec, Canada, was subjected during three consecutive growing seasons (2009–2011) to (i) experimentally increased soil temperature (4 °C) and earlier snowmelt (2–3 weeks) as well as (ii) increased inorganic N concentration in artificial precipitation (3 x current N concentrations using 15NH4- 15NO3). Soil inorganic N was measured using buried ion-exchange membranes (PRS™ probes) and standard soil extractions. Dendrometers were used to monitor the variations in diameter growth and needles were analyzed annually for N to assess the nutritional response of trees. Results from the second (2010) and third (2011) year of treatment are reported.
After three years of treatment, there was no significant increase in soil nitrate (NO3) or ammonium (NH4) availability either in the organic or in the mineral soil as measured with standard soil extractions. Similar results were obtained with ion-exchange membranes, except for NH4 in the forest floor, which increased by an average of 54% over the two years. No effect of treatments was observed on needle N or diameter growth, but an 8-day earlier peak in diameter growth was measured in heated plots in 2010.
We attributed the limited effects of our treatments to the acute soil competition for available N at the site. As a result, the projected modifications of the forest N cycle and concomitant increased forest growth due to an earlier snowmelt, increased soil temperature and N deposition should be considered with caution in similar cold N-poor ecosystems.
by Marie-Claude Boileau | 30 January 2019
Published in Tree Physiology 34(2): 194-204. doi: 10.1093/treephys/tpt114
We examined the ecophysiology and growth of 0.31.3 m tall advance red spruce (Picea rubens Sarg.) and balsam fir (Abies balsamea [L.] Mill.) regeneration during a 5-year period following the application of different harvest types producing three sizes of canopy openings: (i) small gaps (<100 m2 in area; SMA) created by partial uniform single-tree harvest; (ii) irregular gaps of intermediate size (100300 m2; INT) created by group-selection harvest (removal of groups of trees, mainly balsam fir, with uniform partial removal between groups); and (iii) large circular gaps (700 m2; LAR) created by patch-selection harvest (removal of trees in 30-m diameter circular areas with uniform partial removal between gaps). An unharvested control (CON) was monitored for comparison. At the ecophysiological level, we mainly found differences in light-saturated photosynthesis of red spruce and specific leaf area of balsam fir among treatments. Consequently, we observed good height growth of both species in CON and INT, but fir surpassed spruce in SMA and LAR. Results suggest that intermediate 100–300 m2 irregular openings create microenvironmental conditions that may promote short-term ecophysiology and growth of red spruce, allowing the species to compete with balsam fir advance regeneration. Finally, results observed for spruce in large 700-m2 openings confirm its inability to grow as rapidly as fir in comparable open conditions.
by Audrey Verreault | 30 January 2019
Published in Tree Genetics & Genomes 10: 965–975. https://doi.org/10.1007/s11295-014-0735-z
Exotic larch (Larix decidua Mill., Larix kaempferi (Lamb.) Carr. and Larix sibirica Ledeb.) and their hybrids have been introduced into Canada to test adaptation and growth for reforestation purposes. For tree breeding operations, provenance trials and seed orchards of exotic larches and their hybrids have been established in arboreta adjacent to natural forest stands of the indigenous species Larix laricina (Du Roi) K. Koch. This proximity offers an opportunity to measure spontaneous hybridization and the recruitment of hybrids. Using a combination of two chloroplast and three mitochondrial DNA markers, we estimated the rate of spontaneous hybridization taking place between native (L. laricina) and exotic (L. decidua, L. kaempferi, L. sibirica) species of larch in two arboreta. More than 5,000 seeds and 1,000 recruits from the two experimental sites were sampled and genetically identified. The occurrence of spontaneous hybridization between L. laricina and the exotics was found both in seeds and from recruits freely established near the plantations. A low hybridization rate (3 % or less) was observed among the seeds of L. laricina maternal trees. Spontaneous native-exotic hybrids were also observed to establish and survive in the environment under the current climatic conditions at a similarly low rate. However, a much higher and variable rate of establishment was observed for recruits with exotic components (up to 34.6 % at one site). These results indicate that the spontaneous hybridization and the recruitment of hybrid and exotic recruits do occur and should be taken into consideration in the management and establishment of plantations of fast-growing species with exotic components.
by Marie-Claude Boileau | 30 January 2019
Published in Forestry 87: 153-164. https://doi.org/10.1093/forestry/cpt048
It is necessary to evaluate how large seedling stock, used as an alternative to chemical herbicide for vegetation management, interacts with the timing of mechanical release (MR) and if use of such stock offers a broader window of intervention for release than conventional stock. Such a context is present in Quebec (Canada), where chemical herbicides were banned from use on public lands in 2001.We thus evaluated the impact of delaying MR on the performance of large spruce seedlings established in a gradient of vegetation zones and competition environments. Fourteen experiments were conducted in Picea glauca or P. mariana plantations in the temperate hardwood (TH), temperate mixedwood or boreal mixedwood vegetation zones. On each site, we established a completely randomized block design with 5–8 replicates, each divided into four plots: (1) control; (2) MR applied the year during which light availability to the planted seedlings averaged 60 per cent of full sunlight (EARLY); (3) MR at EARLY + 1 year (LATE1); and (4) MR at EARLY + 2 years (LATE2). Vegetation data collected in controls 8 years after MR was submitted to a correspondence analysis to group the sites according to their competing species dominance. Seedling responses to the timing of MR, 5–8 years after treatment, varied across competing vegetation dominance, vegetation zone or a combination of both.On sites where intolerant hardwoods were dominant, postponing MR 1 year after light availability had reached 60 per cent of full sunlight had a positive effect on seedling dimensions, especially in the TH zone. However, the LATE2 treatment resulted in significant stem volume losses on these sites. Whereas treatment effects were limited on ericaceous dominated sites, MR promoted seedling growth on sites dominated by shrub/herbaceous species, with no difference between EARLY, LATE1 and LATE2.
by André Boily | 30 January 2019
Proceedings published in Digital Soil Assessments and Beyond. Minasny, B., B.P. Malone et A.B. McBratney (eds.). April 10-13, 2012. Sydney, Australie. p. 381-386.
