Digital mapping of soil texture in ecoforest polygons in Quebec, Canada

Texture strongly influences the soil’s fundamental functions in forest ecosystems. In response to the growing demand for information on soil properties for environmental modeling, more and more studies have been conducted over the past decade to assess the spatial variability of soil properties on a regional to global scale. These investigations rely on the acquisition and compilation of numerous soil field records and on the development of statistical methods and technology. Here, we used random forest machine learning algorithms to model and map particle size composition in ecoforest polygons for the entire area of managed forests in the province of Quebec, Canada. We compiled archived laboratory analyses of 29,570 mineral soil samples (17,901 sites) and a set of 33 covariates, including 22 variables related to climate, five related to soil characteristics, three to spatial position or spatial context, two to relief and topography, and one to vegetation. After five repeats of 5-fold cross-validation, results show that models that include two functionally independent values regarding particle size composition explain 60%, 34%, and 78% of the variance in sand, silt and clay fractions, respectively, with mean absolute errors ranging from 4.0% for the clay fraction to 9.5% for the sand fraction. The most important model variables are those observed in the field and those interpreted from aerial photography regarding soil characteristics, followed by those regarding elevation and climate. Our results compare favorably with those of previous soil texture mapping studies for the same territory, in which particle size composition was modeled mainly from rasterized climatic and topographic covariates. The map we provide should meet the needs of provincial forest managers, as it is compatible with the ecoforest map that constitutes the basis of information for forest management in Quebec, Canada

Natural regeneration potential and dynamics in boreal lichen woodlands of eastern Canada following soil scarification

Boreal lichen woodlands (LWs) are stable low tree-density zones of the Canadian boreal forest whose afforestation has been proposed as a way to create new C sinks and thus mitigate climate change. Planting operations in these remote areas are however costly and time-consuming, and may not be necessary when soil scarification is followed by dense natural regeneration. In the present study, we assessed the natural regeneration potential and dynamics in six boreal LWs of Québec, Canada, 11 years after soil scarification. The number, size (height and stem diameter) and age of seedlings were measured in 2-4 sampling plots per site (18 plots in total). Our data show that scarification operations produced on average 1,400 m2 ha–1 of exposed mineral soil (scarification intensity of 14%) with, however, a large within-site variability. The natural regeneration was mainly composed of black spruce seedlings (> 95%), averaged ∼12,000 seedlings ha–1 across the six sites and significantly varied among sites, mostly due to the variation in scarification intensity. Seedling density averaged ∼9 seedlings m–2 of exposed mineral soil and increased with seed tree mean diameter at breast height (DBH) (R2 = 0.51; P < 0.05) but not with the density of seed trees, revealing the importance of old and large seed trees in natural regeneration success. Together, scarification intensity and the DBH of remaining seed trees explained ∼60% of the variation in natural regeneration density across the 18 sampled plots. The rate of establishment of seedlings was generally high – with on average 60% of the carrying capacity of the substrate being reached within three years following scarification – and increased with seed tree mean DBH (R2 = 0.77; P < 0.05). However, the growth rate of seedlings was very low. Eleven years after scarification, 60% of the seedlings were < 15 cm and the height of 10-yr-old seedlings averaged 27.5 cm. Thus, even though seedling establishment was successful, the biomass accumulated by the natural regeneration was negligible in the span of a decade. Therefore, the implementation of afforestation following scarification appears to be necessary to create significant C sinks in the midterm

Nine years of in situ soil warming and topography impact the temperature sensitivity and basal respiration rate of the forest floor in a Canadian boreal forest

The forest floor of boreal forest stores large amounts of organic C that may react to a warming climate and increased N deposition. It is therefore crucial to assess the impact of these factors on the temperature sensitivity of this C pool to help predict future soil CO2 emissions from boreal forest soils to the atmosphere. In this study, soil warming (+2–4°C) and canopy N addition (CNA; +0.30–0.35 kg·N·ha-1·yr-1) were replicated along a topographic gradient (upper, back and lower slope) in a boreal forest in Quebec, Canada. After nine years of treatment, the forest floor was collected in each plot, and its organic C composition was characterized through solid-state 13C nuclear magnetic resonance (NMR) spectroscopy. Forest floor samples were incubated at four temperatures (16, 24, 32 and 40°C) and respiration rates (RR) measured to assess the temperature sensitivity of forest floor RR (Q10 = e10k) and basal RR (B). Both soil warming and CNA had no significant effect on forest floor chemistry (e.g., C, N, Ca and Mg content, amount of soil organic matter, pH, chemical functional groups). The NMR analyses did not show evidence of significant changes in the forest floor organic C quality. Nonetheless, a significant effect of soil warming on both the Q10 of RR and B was observed. On average, B was 72% lower and Q10 45% higher in the warmed, versus the control plots. This result implies that forest floor respiration will more strongly react to changes in soil temperature in a future warmer climate. CNA had no significant effect on the measured soil and respiration parameters, and no interaction effects with warming. In contrast, slope position had a significant effect on forest floor organic C quality. Upper slope plots had higher soil alkyl C:O-alkyl C ratios and lower B values than those in the lower slope, across all different treatments. This result likely resulted from a relative decrease in the labile C fraction in the upper slope, characterized by lower moisture levels. Our results point towards higher temperature sensitivity of RR under warmer conditions, accompanied by an overall down-regulation of RR at low temperatures (lower B). Since soil C quantity and quality were unaffected by the nine years of warming, the observed patterns could result from microbial adaptations to warming

Greenhouse gas emissions after application of landfilled paper mill sludge for land reclamation of a nonacidic mine tailings site

Large areas of mine tailings are reclaimed by applying organic amendments such as paper mill sludge (PMS). Although mining industries can use PMS freshly generated by paper mills, operational constraints on paper industries make temporary landfilling of this material an unavoidable alternative for the paper industries, creating the most prominent PMS source for mining industries. This study aimed to quantify soil greenhouse gas (GHG) emissions (N2O, CO2, and CH4) after application of landfilled PMS (LPMS; i.e., excavated from a landfill site at a paper mill) and LPMS combined with a seeding treatment of white clover (Trifolium repens L.) on nonacidic mine tailings site prior to reforestation. Soil N2O, CO2, and CH4 fluxes were measured after applications of 50 and 100 Mg dry LPMS ha−1 during two consecutive snowfree seasons on two adjacent sites; LPMS was applied once in the first season. The LPMS application increased N2O emissions (7.6 to 34.7 kg N2O-N ha−1, comprising 1.04 to 2.43% of applied N) compared with the unamended control during the first season; these emissions were negligible during the second season. The LPMS application increased CO2 emissions (~5800 to 11,400 kg CO2–C ha−1, comprising 7 to 27% of applied C) compared with the unamended control on both sites and in both seasons. Fluxes of CH4 were negligible. White clover combined with LPMS treatments did not affect soil GHG emissions. These new GHG emission factors should be integrated into life-cycle analyses to evaluate the C footprint of potential symbioses between the mining and paper industries. Future research should focus on the effect of PMS applications on soil GHG emissions from a variety of mine tailings under various management practices and climatic conditions to plan responsible and sustainable land reclamation

Relationships between Structure, Composition, and Dynamics of the Pristine Northern Boreal Forest and Air Temperature, Precipitation, and Soil Texture in Quebec (Canada)

This study reports on the contemporary structure, composition, and dynamics of the pristine northern boreal forest in Quebec, Canada, associated with air temperature, precipitation, and soil texture, using 147 permanent sample plots located at the limit of continuous forest in Quebec. The results show that tree species composition of stands is associated with stand age, soil texture, air temperature, and precipitation regime. After establishment of the pioneer cohort, the postsuccessional stand dynamics differed among temperature and precipitation regimes, probably because of their influence on tree growth. Our results support the hypothesis that shifts in forest composition related to stand dynamics and the subsequent senescing phase associated with the old growth stage generally occur sooner and proceed faster on more fertile sites due to quicker growth and the subsequent earlier mortality of pioneer species. This study suggests that climate warming should accelerate the successional dynamics of these ecosystems through its positive influence on tree growth

Long-Term Soil Fertility and Site Productivity in Stem-Only and Whole-Tree Harvested Stands in Boreal Forest of Quebec (Canada)

Using residual biomass from forest harvesting to produce energy is viewed increasingly as a means to reduce fossil fuel consumption. However, the impact such practices on soil and future site productivity remains a major concern. We revisited 196 forest plots that were subject to either whole-tree (WTH) or stem-only (SOH) harvesting 30 years ago in the boreal forest in Quebec, Canada. Plots were stratified by four soil regions grouped by so-called ‘soil provinces’. Soil analyses indicated that after 30 years, the forest floor of WTH sites had smaller pools of N (−8%), exchangeable Ca (−6%) and exchangeable Mn (−21%) and a higher C/N ratio (+12%) than that of SOH sites. Mineral soil responses to the two harvesting intensities differed among soil provinces. In the two coarse-textured granitic soil provinces, organic matter, organic carbon, and nitrogen pools over the whole solum (0–60 cm soil depth) were at least 28% smaller after WTH than after SOH. Site productivity indicators followed differences between soils and were lower after WTH than after SOH in the two granitic soil provinces. The study shows that soil characteristics greatly influence a soil’s sensitivity to increased forest biomass harvesting in the long term

Soil Texture Explains Soil Sensitivity to C and N Losses from Whole-Tree Harvesting in the Boreal Forest

The use of forest biomass to produce energy is increasingly viewed as a means to reduce fossil fuel consumption and mitigate global warming. However, the impact of such practices on soils in the long term is not well known. We revisited forest plots that were subjected to either whole-tree (WTH, n = 86) or stem-only (SOH, n = 110) harvesting 30 years ago in the boreal forest in Quebec, Canada. The objective of the present study was to find soil properties that could explain the lower soil C and N stocks at the sites subjected to WTH compared to SOH after 30 years. Compared to SOH, lower soil C and N stocks attributable to WTH occurred when soil particle content <20 µm was below 30%. The theoretical separation of soil organic matter into two fractions according to soil particle content <20 µm—a recalcitrant and a labile fraction—could explain the observed pattern of soil C and N differences between WTH and SOH. Imperfect or poor soil drainage conditions were also associated with lower soil C and N in WTH compared to SOH. Limiting additional biomass harvesting from these sites would help to preserve soil C and N from potential losses

Relation entre la composition foliaire et la présence de la maladie corticale du hêtre dans les stations du Réseau d’étude et de surveillance des écosystèmes forestiers du Québec

La maladie corticale du hêtre (MCH) est de plus en plus fréquente dans les forêts de l’est de l’Amérique du Nord. Des chercheurs ont avancé l’hypothèse que l’expansion de cette maladie pourrait être en partie liée au statut nutritif des arbres. Pour tester cette hypothèse, nous avons vérifié la relation entre l’apparition de cette maladie et la composition du feuillage du hêtre (Fagus grandifolia Ehrh.) dans les stations du Réseau d’étude et de surveillance des écosystèmes forestiers du Québec. Sur les 14 stations contenant du hêtre, cinq présentaient des symptômes de la maladie entre 2006 et 2012. Les arbres infectés étaient en moyenne de plus grand diamètre que ceux qui ne l’étaient pas. La présence de la MCH était liée en partie à la composition foliaire des arbres (pseudo-R2 : 0,551). L’analyse indique que plus le rapport N/P du feuillage du hêtre est élevé, plus la probabilité d’infection par la MCH est importante; et plus les rapports Zn/Mn et Mg/K du feuillage sont élevés, plus la probabilité d’infection par la MCH est faible. Ces rapports donnent à penser que les conditions d’acidification du sol et de drainage influencent la vigueur des arbres et, conséquemment, leur vulnérabilité à la MCH.Beech bark disease (BBD) is becoming more and more frequent in forests of eastern North America. Researchers are bringing forward the hypothesis that the expansion of this disease could partly be related to the trees’ nutrient status. To test this hypothesis, we evaluated the relationship between the occurrence of BBD and the foliage composition of beech (Fagus grandifolia Ehrh.) in plots of the Quebec Forest Ecosystems Study and Monitoring Network. In the 14 plots where beech was present, five displayed BBD symptoms between 2006 and 2012. On average, infected trees had a greater diameter than uninfected trees. The occurrence of BBD was associated in part to tree foliage composition (pseudo-R2: 0.551). The analysis shows that the higher the N/P ratio of the foliage, the higher the probability of infection by BBD; and the higher the Zn/Mn and Mg/K ratios of the foliage, the lower the probability of infection by BBD. These ratios suggest that soil acidification and drainage conditions influence tree vigour and, consequently, its vulnerability to BBD infection

Évolution du statut nutritif des sapinières à la Forêt Montmorency entre 1967 et 2011

Cette étude avait pour objectif d’évaluer l’évolution du statut nutritif des sapinières de la Forêt Montmorency en se basant sur des analyses foliaires faites en 1967, 1988 et en 2011. La composition minérale des aiguilles du sapin baumier (Abies balsamea) a grandement fluctué au cours de ces 45 ans. Entre 1967 et 2011, nous avons observé une baisse de 5,7 % des teneurs en azote dans le feuillage, de 13,5 % des teneurs en potassium (aiguilles âgées de 1 an) et de 18 % des teneurs en magnésium (aiguilles âgées de 2 et de 3 ans). En 1988, les teneurs étaient en général beaucoup plus faibles que celles observées lors des 2 autres campagnes d’échantillonnage. Cette baisse peut s’expliquer en partie par le choix des peuplements visités, la hausse des précipitations acides depuis le début des années 1970, les épidémies d’insectes ravageurs et les extrêmes climatiques. Les teneurs en potassium du feuillage âgé de 1 an demeurent plus faibles que celles rapportées ailleurs dans la littérature pour le sapin baumier. La baisse des teneurs en potassium et en magnésium de 1967 à 2011 laisse croire à une perte de fertilité des sols dans cette région au cours des 45 dernières années.The objective of this study was to use foliage analyses conducted in 1967, 1988 and 2011, to assess the evolution of the nutritional status of balsam fir (Abies balsamea) stands at the Montmorency Forest (Québec). The elemental composition of balsam fir needles varied greatly over the 45-year study period. Between the 1967 analysis and that of 2011, the foliar nitrogen concentration decreased by 5.7%; the potassium concentration in 1-year-old needles, by 13.5%, and the magnesium concentration in 2- and 3-year-old needles, by 18%. The mineral concentrations in the tissues analysed in 1988 were much lower than those of the other 2 samplings. This decrease can be explained partly by the choice of the stands sampled, the increase of atmospheric acid precipitation since the 1970s, the effects of past insect outbreaks, and climatic extremes. Potassium concentrations in 1-year-old needles were lower than values reported elsewhere for balsam fir. The decreases in foliar potassium and magnesium concentrations from 1967 to 2011 suggest a loss of soil fertility in this region over the last 45 years

Prolifération des fougères dans les érablières du Québec : ampleur du phénomène et moyens de le contrer

L’envahissement des érablières par les fougères est un phénomène de plus en plus fréquent au Québec. Les espèces de fougères envahissantes étudiées ici sont surtout associées à des conditions de drainage imparfait du sol, périodiquement inondé, et à des humus > 14 cm d’épaisseur. L’occurrence de ces espèces de fougères dans les érablières est aussi corrélée à la densité de cerfs de Virginie sur le territoire. Nous avons testé, dans 2 expériences, divers traitements pour favoriser la régénération en érable dans des érablières envahies par Dennstaedtia punctilobula. Seule la combinaison du chaulage et soit de la fauche soit de l’écrasement à répétition des fougères a accru considérablement la densité de semis d’érable après 3 à 5 ans, atteignant 15 à 28 semis/m2. L’écrasement à répétition des fougères ou la pose d’ombrières en sous-bois a aussi réduit de 30 % et plus la densité et la hauteur des fougères. Les observations mettent en lumière la dynamique complexe entre l’ouverture du couvert forestier, l’occurrence de fougères envahissantes, les conditions de fertilité du sol et le broutage par les cerfs, qui influencent l’abondance de la régénération en érable dans les érablières.The invasion of sugar maple stands or sugarbushes by ferns is becoming increasingly more common in Québec (Canada). The invasive fern species investigated in the present study are mainly associated with poorly drained soil that is periodically waterlogged and which has a forest humus layer >14 cm. The occurrence of invasive fern species in sugar maple stands is also related to an increase in the density of white-tail deer. In 2 experiments, various treatments aimed at promoting maple regeneration in stands invaded by Dennstaedtia punctilobula, were tested. Only the combination of liming and repeated mowing or flattening of the ferns led to a considerable increase in the density of maple seedling in the understory, reaching 15 to 28 seedlings/m2 after 3 to 5 years. Both repeated flattening of fronds and artificial shading of the understory also decreased frond density and height by at least 30%. The results highlight the complex interactions between openings in the forest canopy, the occurrence of invasive ferns, dear browsing and soil fertility that influence maple regeneration in sugarbushes