by Marie-Claude Boileau | 30 January 2019
Published in Tree Planters’ Notes 52(2): 18-23
Direct seeding and fill planting of black spruce [Picea mariana (Mill.) B.S.P.] were assessed in logging trails after irregular shelterwood cutting in the boreal forest of Québec, Canada. Two growing seasons after harvest, direct seeding increased seedling establishment when compared to control plots, but seeded seedling density represented only 17 percent of seeds initially deposited. Seedling establishment increased with increasing soil moisture. Planted container seedlings responded well with mean terminal shoot growth of 4.7 cm (1.9 in) yr-1. Terminal shoot growth of planted seedlings decreased with increasing soil moisture. Results suggest potential for improvement of logging trail regeneration with fill planting.
by Audrey Verreault | 30 January 2019
Published in Global Change Biology 17(6): 2227–2244
Canada’s forests play an important role in the global carbon (C) cycle because of their large and dynamic C stocks. Detailed monitoring of C exchange between forests and the atmosphere and improved understanding of the processes that affect the net ecosystem exchange of C are needed to improve our understanding of the terrestrial C budget. We estimated the C budget of Canada’s 2.3 x 106 km2 managed forests from 1990 to 2008 using an empirical modelling approach driven by detailed forestry datasets. We estimated that average net primary production (NPP) during this period was 809 + 5 TgCyr-1 (352 gCm-2 yr-1) and net ecosystem production (NEP) was 71 + 9 TgCyr-1 (31 gCm-2 yr-1). Harvesting transferred 45 + 4 TgCyr-1 out of the ecosystem and 45 + 4 TgCyr-1 within the ecosystem (from living biomass to dead organic matter pools). Fires released 23 + 16 TgCyr-1 directly to the atmosphere, and fires, insects and other natural disturbances transferred 52 + 41 TgCyr-1 from biomass to dead organic matter pools, from where C will gradually be released through decomposition. Net biome production (NBP) was only 2 + 20 TgCyr-1 (1 gCm-2 yr-1); the low C sequestration ratio (NBP/NPP = 0.3%) is attributed to the high average age of Canada’s managed forests and the impact of natural disturbances. Although net losses of ecosystem C occurred during several years due to large fires and widespread bark beetle outbreak, Canada’s managed forests were a sink for atmospheric CO2 in all years, with an uptake of 50 + 18 TgCyr-1 [net ecosystem exchange (NEE) of CO2=-22 gCm-2 yr-1].
by Audrey Verreault | 30 January 2019
Published in Ecological Applications 20(5): 1302-1319
Climate change has altered the environment in which forests grow, and climate change models predict more severe alterations to come. Forests have already responded to these changes, and the future temperature and precipitation scenarios are of foremost concern, especially in the mountainous western United States, where forests occur in the dry environments that interface with grasslands. The objective of this study was to understand the trade-offs between temperature and water controls on these forested sites in the context of available climate projections. Three temperature and precipitation scenarios from IPCC AR4 AOGCMs ranging in precipitation levels were input to the process model Biome-BGC for key forested sites in the northern U.S. Rocky Mountains. Despite the omission of natural and human-caused disturbances in our simulations, our results show consequential effects from these conservative future temperature and precipitation scenarios. According to these projections, if future precipitation and temperatures are similar to or drier than the dry scenario depicted here, high-elevation forests on both the drier and wetter sites, which have in the absence of disturbance accumulated carbon, will reduce their carbon accumulation. Under the marginally drier climate projections, most forests became carbon sources by the end of the simulation horizon (2089). Under all three scenarios, growing season lengthened, the number of days with snow on the ground decreased, peak snow occurred earlier, and water stress increased through the projection horizon (1950–2089) for all sites, which represent the temperature and precipitation spectrum of forests in this region. The quantity, form, and timing of precipitation ultimately drive the carbon accumulation trajectory of forests in this region.
by Marie-Claude Boileau | 30 January 2019
Published in Canadian Journal of Plant Science 91: 725-738
Rhododendron groenlandicum (Oeder) Kron and Judd, bog Labrador tea, is an evergreen shrub from the Ericacae family native to North America. Bog Labrador tea is associated with the later stages of forest successions in black spruce forest stands of the boreal ecosystems with cool climates, but responds aggressively to forest openings where it is already present. In general, bog Labrador tea is associated with nutrient-poor, acidic soils, with drainage ranging from moist to wet. Layering is the main regeneration strategy of the species; evidence suggests that this could be especially true following disturbances that open the forest canopy. Sexual reproduction maintains viability in undisturbed communities through wind or water dispersal. Rhododendron groenlandicum acclimates more rapidly relative to black spruce after perturbations through a higher rate of resource utilization when resources are available. The species is a highly competitive shrub for soil nutrients; it competes with regenerating conifers for soil nitrogen and phosphorus. It can also assimilate organic nitrogen from the soil through its mycorhizae. These characteristics may lead to the formation of ericaceous heaths that can stay unforested indefinitely. However, this species can be eradicated by herbicides (glyphosate) and heavy site scarification can limit its propagation.
by Audrey Verreault | 30 January 2019
Published in Forest Ecology and Management 255: 3659-3666
American beech (Fagus grandifolia Ehrh.) reproduces sexually, and vegetatively by root suckers. Although many studies have investigated its regeneration response, most did not account for differences that may exist between its two modes of reproduction. This study was performed in an old-growth Acer – Fagus forest in southern Quebec, where beech bark disease had only a minor effect at the time of the study. We compared the density and frequency of occurrence of beech seedlings and root suckers (height < 30 cm), as well as their morphology, growth, survival, and response to experimental defoliation. Root suckers accounted for ~13% of beech regeneration at our site. Density and frequency of occurrence were greater for seedlings than suckers, but did not vary with light availability, which was low at our study site (mean: 2.9%). Seedlings and suckers did not differ in leaf characteristics, but several differences were observed in terms of plant morphology, growth, and survival. Root suckers showed more lateral growth than height growth, and had a lower leaf area index than seedlings. Root suckers had both a greater growth in height and diameter, and a higher survivorship than seedlings (height and diameter growth were, respectively, five and two times greater for suckers than seedlings, and 74% of suckers survived more than 1 year, compared to 52% for seedlings). Defoliation treatments, which included levels of defoliation of 50% and 100% (1) did not affect current-year extension growth of seedlings and suckers; (2) did not affect seedling diameter growth, but had a negative impact on sucker diameter growth; and (3) affected survivorship for both origins, but had a much greater negative impact on seedling survivorship (none of the completely defoliated seedlings survived over one year, while 55% of the suckers did). This study showed that several differences exist between small beech seedlings and root suckers in traits that are important determinants of a species’ competitive ability. We therefore expect that variation in the relative importance of root suckering among sites might have several community-level implications.
