by Audrey Verreault | 30 August 2024
Published in Canadian Journal of Forest Research (e-First). https://doi.org/10.1139/cjfr-2024-0009
Commercial thinning is a silvicultural treatment that has been practiced for centuries in Europe. However, in Eastern Canada, its application to naturally regenerated stands is much more recent, and long-term monitoring of this treatment realized in an operational context is rare. We monitored 135 paired sample plots (thinned and control) over a 20-year period. The plots are in stands dominated by either black spruce (Picea mariana (Mill.) B.S.P.), jack pine (Pinus banksiana Lamb.), or balsam fir (Abies balsamea (L.) Mill.) and distributed throughout the boreal and temperate forests of Québec (Canada). Twenty years after treatment, thinning increased quadratic mean diameter (QMD) for balsam fir (1.7 cm) and jack pine (0.7 cm), while for black spruce the change in QMD varied according to the QMD before treatment. Periodic annual increment in gross merchantable volume of thinned and control plots was similar for balsam fir and jack pine but was less in thinned black spruce plots during the first 5 years. Thinning did not affect mortality, which remained low until 15 years after treatment. As commercial thinning should gain popularity over the next years, our study provides a benchmark of the expected effects when the treatment is performed in an operational context.
by Audrey Verreault | 20 August 2024
Published in The Forestry Chronicle 100(2): 1-12. https://doi.org/10.5558/tfc2024-023
Repeated diameter-limit cutting in mixedwood forests often leads to altered stand composition, quality, and regeneration, hence decreasing productivity and value over time. We studied the evolution of stand characteristics after diameter-limit cutting on a 15-year period, beginning from 11 to 43 years after cutting. We used 415 sample plots (200 m2) and three criteria: (i) ≥9.0 m2/ha overstory (trees ≥9.1 cm dbh [diameter at breast height, 1.3 m above ground]) acceptable growing stock (AGS, i.e. basal area of vigorous trees with sawlog potential), (ii) ≥3.0 m2/ha pole timber AGS (9.1 cm-23.0 cm dbh) and (iii) ≥60% sapling (dbh 1.1-9.0 cm) stocking of desired species. Stand initial quality was determined in function of overstory AGS at the beginning of the monitoring period: good quality (AGS≥9.0 m2/ha), impoverished (7.0≤AGS< 9.0 m2/ha), degraded (AGS <7.0 m2/ha). After 15 years, 47% of stands satisfied at least two criteria, but most stands (65%) had insufficient sapling regeneration. Stands in good quality and impoverished categories had sufficient basal area and AGS to support a new partial cutting cycle, contrary to stands in the degraded category. A conceptual model based on these three criteria is presented to guide silvicultural rehabilitation of uneven-aged mixedwood stands altered by past cutting practices.
by Audrey Verreault | 2 August 2024
Published in Forest Ecology and Management 568: 122069. https://doi.org/10.1016/j.foreco.2024.122069
Litterfall is a major pathway for transferring aboveground biomass to the forest floor and thus plays an important role in building forest soil carbon stocks. However, inter- and intra-annual variability of litterfall remains poorly documented, especially in North American temperate and boreal forests, due to the lack of recent long-term studies at high sampling frequencies. This potentially creates uncertainties in estimates of forest carbon budget models. The objectives of the present study were to 1) quantify the mean annual flux, interannual variability, and seasonality of litterfall in three sites (dominated respectively by sugar maple (Acer saccharum Marsh.), balsam fir (Abies balsamea (L.) Mill. 1768), and black spruce (Picea mariana (Mill.) B.S.P.)) in eastern Canada over a period of 22–32 years, 2) relate the litterfall amounts and temporal variations to the changes in the size of major organic matter pools in these ecosystems, and 3) compare our litterfall estimates with reference values used in national greenhouse gas inventories. Litterfall production decreased from the sugar maple to the balsam fir and black spruce sites, preponderantly due to species composition. Litterfall evolution was related to the aboveground biomass of live trees in both conifer sites; in contrast, in the broadleaf site, changes in forest composition and structure were apparently the main drivers. The litterfall seasonality varied between broadleaf and conifer sites and could be explained by a sigmoidal model. Substantial departures from the seasonality for some given years were likely due to important climatic anomalies. Forest floor biomass remained stable over time at all three sites despite the increase in litterfall at the balsam fir and sugar maple sites and rapid forest floor turnover at the latter site. Our analyses of litterfall suggest that reference values from the literature used for national greenhouse gas inventories underestimate annual litterfall and forest floor carbon stocks for temperate and boreal forests.
by Audrey Verreault | 25 July 2024
Published in The Leaflet – Northen Hardwood Research Institute – NHRI 6(2) p. 11-16
Little known until recently in North America, the practice of irregular shelterwood system (ISS) is gaining popularity, because it meets the management needs of natural stands with an irregular structure, i.e., stands that are neither even-aged nor balanced uneven-aged. In Québec for example, research by the Direction de la recherche forestière (DRF) of the ministère des Ressources naturelles et des Forêts has led to application guidelines for the main forest types published in 2013 in the provincial silvicultural guide. Since then, some 20,000 ha of public forests have been treated in this way every year, particularly to meet ecosystem management objectives. Given its ability to promote stand structural and compositional complexity, this silvicultural system could prove to be an asset in promoting resilience in the face of global change.
by Audrey Verreault | 5 July 2024
Published in Science of The Total Environment 946: 174387. https://doi.org/10.1016/j.scitotenv.2024.174387
Northern temperate and boreal forests are large biomes playing crucial ecological and environmental roles, such as carbon sequestration. Despite being generally remote, these forests were exposed to anthropogenic nitrogen (N) deposition over the last two centuries and may still experience elevated N deposition as human activities expand towards high latitudes. However, the impacts of long-term high N deposition on these N-limited forest ecosystems remain unclear. For 18 years, we simulated N deposition by chronically adding ammonium nitrate at rates of 3 (LN treatment) and 10 (HN treatment) times the ambient N deposition estimated at the beginning of the experiment at a temperate sugar maple and a boreal balsam fir forest site, both located in northeastern America. LN and HN treatments corresponded respectively to addition of 26 kgN⋅ha-1⋅yr-1 and 85 kgN⋅ha-1⋅yr-1 at the temperate site and 17 kgN⋅ha-1⋅yr-1 and 57 kgN⋅ha-1⋅yr-1 at the boreal site. Between 2002 and 2018, soil solution was collected weekly during summer and concentrations of NO3– , NH4+, Ca2+ and pH were measured, totalling ~12,700–13,500 observations per variable on the study period. N treatments caused soil solution NO3–, NH4+ and Ca2+ concentrations to increase while reducing its pH. However, ion responses manifested through punctual high concentration events (predominantly on the HN plots) that were very rare and leached N quantity was extremely low at both sites. Therefore, N addition corresponding to 54 years (LN treatment) and 180 years (HN treatment) of accelerated ambient N deposition had overall small impacts on soil solution chemistry. Our results indicate an important N retention of northeastern American forests and an unexpected strong resilience of their soil solution chemistry to long-term simulated N deposition, potentially explained by the widespread N-limitation in high latitude ecosystems. This finding can help predict the future productivity of N-limited forests and improve forest management strategies in northeastern America.
