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Ongoing rapid climatic changes are expected to modify the structure, composition, and functioning of forest ecosystems. Studying the influence of such changes on biogeochemical processes is thus crucial for a fuller understanding of forest response to climate change. In a temperate forest of Quebec, Canada, we emulated climate change by warming the acidic, nutrient-poor, and dry soils of two mixedwoods by 3 to 4 °C using heating cables. Leaf-litter mass loss of the local red maple, sugar maple, large-tooth aspen, and American beech were monitored to assess the ability of these tree species to condition boreal soils in the context of their northward migration under climate change. We hypothesized that decomposition rates of all leaf-litter types would be decreased equally by warming due to a drying effect of the soil and its surface, which is detrimental to microbial biomass and activity. Our results suggest differences in decomposition rates between tree species as follows: sugar maple > red maple ≥ American beech = large-tooth aspen. There was no indication of a slower turnover in these marginal soils compared to other studies conducted on typical hardwood soils. Moreover, no difference in litter mass loss was detected between treatments, likely due to a drying effect of the soil warming treatment. Results imply that climate change has a marginal influence on leaf-litter dynamics of temperate tree species on soils that are typical of the boreal forest. However, some variables that could play an important role on litter decomposition in the context of climate change were not measured (e.g., plant phenology, understory composition and density, microbes) and thus, uncertainties remain. The soil drying effect by warming also needs to be further documented and modeled. The study year was characterized by significant periods of water stress but was not considered an exceptional year in that regard. It would be relevant to test for leaf-litter dynamics during dry and wet summers and verify again our initial hypothesis of decreased leaf-litter decomposition rates due to soil warming/drying. [ABSTRACT FROM AUTHOR]

Wood ash fertilization has yet to be investigated in Canadian boreal forests. Ash often improves soil acid–base status, but without N addition it seldom increases tree growth on poor mineral soils. We report results of a large scale experiment conducted in a boreal jack pine ( Pinus banksiana Lamb) stand growing on sandy acidic soil in Northeastern Canada. The experiment was completely random with four replications (1 ha each) of five treatments (0, 1, 2, 4 and 8 dry Mg ha −1 ) of loose fly ash with and without urea (280 kg N ha −1 ). Soils were sampled in the 0, 2, and 8 Mg ha −1 treatment up to eight years after application. Foliar nutrition and stand growth were assessed in all treatments one and two years and five years after treatment, respectively. Even under low ash loading, forest floor exchangeable base cations, pH, and base saturation increased within a year of application. Ash application also resulted in a swift decrease in forest floor organic C and an increase in N potential net mineralization rate. The initial dominant pattern of upper mineral soil properties in relation to ash loading was a curvilinear relationship with the highest values observed in the 2 Mg ha −1 treatment. Eight years after ash application, significant linear relationships were found between ash loading and base cations and base saturation in the forest floor and mineral soil (0–10 cm, 10–20 cm). Contrary to N fertilization, ash had no effect on jack pine foliar nutrition and on its five-year growth. However, a decrease of 30% in relative growth rate was observed between the control and the 8 Mg ha −1 ash treatment for large (⩾10 cm DBH) black spruces ( Picea mariana (Mill.) BSP). Black spruce is the dominant commercial species of Canadian eastern boreal forests and thus, additional studies are needed to validate the deleterious effect of ash on spruce growth and to elucidate the mechanisms involved. [ABSTRACT FROM AUTHOR]

Background and Aims: Reduced availability of calcium (Ca) has been linked to maple forest decline. We therefore aimed at assessing the contribution of the different soil horizons to leaf Ca of competing beech ( Fagus grandifolia Ehrh.) and sugar maple ( Acer saccharum Marsh.) to better understand the dynamics of Ca uptake. Methods: Leaf Ca was partitioned using the Ca/Sr ratio approach in two mature forests of southern Quebec. A mass balance was also used at one site to validate the results obtained with the Ca/Sr approach. Results: The L and F horizons contributed most of the leaf Ca of beech and maple with likely small contributions from the upper B and/or H/Ahe horizons. Leaf Ca/Sr ratios of beech were however more variable than those of maple. Using a mass balance, the organic horizons and upper mineral soil horizons were found to provide ca. 80 and 20 % of tree Ca uptake, respectively. Conclusion: Beech and maple Ca uptake depth apportionment is on average similar but beech is likely more plastic in sourcing soil Ca. The low contribution of the mineral soil to leaf Ca at our sites can be linked to less favorable conditions for Ca uptake likely associated with low Ca/Al ratios. [ABSTRACT FROM AUTHOR]

An important tenet of the natural disturbance paradigm as a basis for sustainable forest management is that impacts of interventions fall within the range of natural variation observed for the disturbance in question. We evaluated differences in soil nutrients, soil acid–base status, and tree nutrition between two harvesting methods (whole-tree (WTH) and stem-only (SOH)) and wildfire, 15–20 years after disturbance, to assess whether these harvesting methods have biogeochemical impacts that are within the natural range of variation caused by wildfires in boreal coniferous stands of Haute-Mauricie (Quebec). Both SOH and WTH created conditions of forest floor effective cation-exchange capacity, exchangeable Ca and K concentrations, base saturation, Ca:Al molar ratio, and organic C concentrations that were lower than the range of values for wildfires. We hypothesize that the immediate deposition of soluble base cations and the incorporation of recalcitrant organic matter that characterize wildfires generate biogeochemical conditions that are not emulated by either harvesting method. The improved soil nutritional environment after wildfire compared with SOH and WTH was reflected in jack pine (Pinus banksiana Lamb.) foliar nutrient composition but not in black spruce (Picea mariana (Mill.) BSP) foliage. The results raise uncertainties about the long-term base nutrient availability of the harvested sites on Boreal Shield soils. [ABSTRACT FROM AUTHOR]

The amount of logging residues left on site after clear-felling has been shown to influence the state of soil nutrient resources, but this effect may depend on soil conditions. In three regions of the boreal zone of Quebec, with contrasting soil characteristics, soil and foliar nutrient status of young (15–20 yr old) stands were compared among sites that were clear-felled at two harvesting intensities, that is, stem-only (SOH) and whole-tree harvesting (WTH). Balsam fir (Abies balsamea) stands were studied in the Forêt Montmorency and Gaspésie regions, while black spruce [Picea mariana (Mill.) B.S.P.] and jack pine (Pinus banksiana Lamb.) were studied in the Haute-Mauricie region. Whole-tree harvesting resulted in lower cation exchange capacity (CEC) compared with SOH, but this effect could be linked to decreased levels of organic C only in the Haute-Mauricie region, where soils had intrinsically low organic matter content. Lower soil and foliar Ca concentrations after WTH were observed in all three regions. Foliar Ca status was most strongly affected by harvesting intensity in Gaspésie, where soils exhibited the lowest concentration of total Ca in the parent material. In Haute-Mauricie, where the parent material contained a low level of Mg, foliar nutrition for this element was significantly poorer under WTH compared with SOH. Harvesting intensity did not influence the biogeochemical cycles of K and N. Foliar analysis revealed that jack pine exhibits the strongest nutritional difference between WTH and SOH. Results suggested that the tree species regenerating the harvested sites, as well as the total Ca and Mg contents of the parent material are better indicators of a site's susceptibility to nutritional alteration by WTH than soil available nutrient status. [ABSTRACT FROM AUTHOR]

The renewed interest in the use of fast-growing tree species is accompanied by concerns about the adverse effects that these trees may have on soil. Four Norway spruce (Picea abies (L.) Karst.) provenance trials in Quebec were used to test the hypothesis that a more vigorous growth would not occur at the expense of marginalizing available nutrient pools. On these sites, the provenance showing the greatest overall productivity (high treatment) and the one showing the lowest productivity (low treatment) were studied. The divergence in total aboveground nutrient contents between the high and low treatments was high in all sites (i.e., 161%–209%). Increased nutrient immobilization in trees did not cause any significant soil depletion of available base cations or total N at any site. Moreover, exchangeable Ca concentrations, cation-exchange capacity, and exchangeable Ca pools in the forest floor were significantly higher in the high treatment. It is concluded that in the short term, increased nutrient immobilization in trees does not create an apparent depletion of available base cations, perhaps because of a stimulation of soil mineral weathering and (or) a better retention of nutrients by the trees. Also, an effort to simulate mineral weathering using PROFILE showed the need for model improvement for applications at the plot level. [ABSTRACT FROM AUTHOR]

The effect of different harvesting practices on soil acid–base status was evaluated in black spruce (Picea mariana (Mill.) BSP) forests of Quebec by comparing soil from five pairs of whole-tree and stem-only harvested plots 3 years after harvest. Stem-only harvesting contributed to the enrichment of the exchangeable base cation pool, particularly in the forest floors of the pairs where whole-tree harvested plots showed the highest exchangeable Al3+. In the mineral soil, divergence between treatments was low, perhaps because these acidic soils were strongly saturated with Al3+ (about 90%), which did not favour cationic exchange reactions. Although the effects of treatment may not persist over time, improved base cation nutrition may benefit stands during the early stages of development. Over a forest rotation of about 85 years, the estimated loss of alkalinity due to whole-tree harvesting was estimated to be low (less than 20%) when compared with the effect of acidic deposition. [ABSTRACT FROM AUTHOR]