Search Results (15)

In northern hardwood forests, litter decomposition might be affected by nutrient availability, species composition, stand age, or access by decomposers. We investigated these factors at the Bartlett Experimental Forest in New Hampshire. Leaf litter of early and late successional species was collected from four stands that had full factorial nitrogen and phosphorus additions to the soil and were deployed in bags of two mesh sizes (63 µm and 2 mm) in two young and two mature stands. Litter bags were collected three times over the next 2 years, and mass loss was described as an exponential function of time represented by a thermal sum. Litter from young stands had higher initial N and P concentrations and decomposed more quickly than litter from mature stands (p = 0.005), regardless of where it was deployed. Litter decomposed more quickly in fine mesh bags that excluded mesofauna (p < 0.001), which might be explained by the greater rigidity of the large mesh material making poor contact with the soil. Neither nutrient addition (p = 0.94 for N, p = 0.26 for P) nor the age of the stand in which bags were deployed (p = 0.36) had a detectable effect on rates of litter decomposition. Full article

The effect of climate change on forest dynamics is likely to increase in importance in the forthcoming decades. For this reason, it is essential to predict the extent to which changes in temperature, precipitation, and atmospheric CO₂ might affect the development of forest ecosystems and successional pathways. The gap model ZELIG-CFS was used to simulate the potential long-term effects of climate change on species-specific annual change in mean basal area and stand density under two scenarios of representative concentration pathways (RCP), 4.5 and 8.5, for the boreal forest region of Ontario, Canada, where mean temperature, precipitation, and atmospheric CO₂ are expected to increase. Forest ecosystems in this boreal region included pure and mixed stands of black spruce (Picea mariana [Mill.] B.S.P.), paper birch (Betula papyrifera Marsh.), balsam fir (Abies balsamea [L.] Mill.), jack pine (Pinus banksiana Lamb.), trembling aspen (Populus tremuloides Michx.), white spruce (Picea glauca [Moench] Voss), northern white cedar (Thuja occidentalis L.), American larch (Larix laricina [Du Roi] K. Koch), and balsam poplar (Populus balsamifera L.). Simulation results under climate change generally predicted a decline in the basal area and stand density for black spruce, balsam fir, jack pine, and white spruce, but an increase for paper birch, trembling aspen, American larch, and balsam poplar. However, the extent of change differed regionally among species. Forest composition is expected to change over the long term. Simulation results indicated that shade-intolerant deciduous and conifer species will increase their dominance over the 100-year time horizon. This transition toward the increasing presence of deciduous forests is likely explained by more favorable temperature conditions for their growth and development. Full article

Diameter at breast height (DBH) is a unique attribute used to characterize forest growth and development for forest management planning and to understand forest ecology. Forest managers require an array of DBHs of forest stands, which can be reconstructed using selected probability distribution functions (PDFs). However, there is a lack of practices that fit PDFs of sub-dominating species grown in natural mixed forests. This study aimed to fit PDFs and develop predictive models for PDF parameters, so that the predicted distribution would represent dynamic forest structures and compositions in mixed forest stands. We fitted three of the simplest forms of PDFs, log-normal, gamma, and Weibull, for the DBH of eight tree species, namely balsam fir (Abies balsamea [L.] Mill.), eastern white pine (Pinus strobus L.), paper birch (Betula papyrifera Marshall), red maple (Acer rubrum L.), red pine (Pinus resinosa Aiton), sugar maple (Acer saccharum Marshall), trembling aspen (Populus tremuloides Michx), and white spruce (Picea glauca [Moench] Voss), all grown in natural-origin mixed forests in Ontario province, Canada. We estimated the parameters of the PDFs as a function of DBH mean and standard deviation for these species. Our results showed that log-normal fit the best among the three PDFs. We demonstrated that the predictive model could estimate the recovered parameters unbiasedly for all species, which can be used to reconstruct the DBH distributions of these tree species. In addition to prediction, the cross-validated R² for the DBH mean ranged between 0.76 for red maple and 0.92 for red pine. However, the R² for the regression of the standard deviation ranged between 0.00 for red pine and 0.69 for sugar maple, although it produced unbiased predictions and a small mean absolute bias. As these mean and standard deviations are regressed with dynamic covariates (such as stem density and stand basal area), in addition to climate and static geographic variables, the predicted DBH distribution can reflect change over time in response to management or any type of disturbance in the regime of the given geography. The predictive model-based DBH distributions can be applied to the design of appropriate silviculture systems for forest management planning. Full article

Atmospheric CO₂ levels have been increasing, and likewise, increasing drought events have been following increasing temperatures. There is very little literature on the effects of climate change factors on early-successional deciduous species used for ecological restoration. Thus, morphological and allometric variation in four coppiced early-successional deciduous species was examined in response to a 2 × 2 factorial of ambient CO₂ (aCO₂, 400 ppm) and elevated CO₂ (eCO₂, 800 ppm), as well as well-watered and drought treatments with 15%–20% and 5%–10% volumetric moisture content, respectively, grown in sandy soil with low soil nitrogen (N) under greenhouse conditions. The four species examined were as follows: green alder (Alnus viridis subsp. crispa (Ait.) Turrill), speckled alder (A. incana subsp. rugosa (Du Roi) R.T. Clausen), gray birch (Betula populifolia (Marshall)), and white birch (B. papyrifera (Marshall)), and all are from the same phylogenetic family, Betulaceae. Genus differences in morphological and growth traits were large, especially in response to the environmental treatments used. Alders upregulated all growth traits under eCO₂ because of the strong coppicing sink effect and the additional foliar N provided by the actinorhizal ability of the genus, whereas birches remained the same or slightly decreased under eCO₂. As a result, alders have a significantly greater foliar N than birches, with 2.8 and 1.0%, respectively. All species reduced growth under drought, and green alder had the greatest stem dry mass growth, followed by speckled alder and then the birches. Under drought, eCO₂ not only mitigated the alder drought dry mass but, in fact, doubled the stem dm, whereas eCO₂ only just mitigated the birches drought response. When corrected for size using stem height, alders allocated more to stem and leaf and less to root dry mass than birches. Atmospheric CO₂ and soil moisture treatments changed organ biomass allocation. The tallest stem height was the best predictor of total (above and below) dry mass. With increasing atmospheric CO₂, particularly on low nutrient sites, the results show alders are capable of sequestering far more carbon than birches. In addition, with more atmospheric CO₂, alders can mitigate against drought conditions better compared to birches. Full article

Barren sites that lack soil are exposed to some of the harshest elements, which include high temperatures, solar radiation, wind, extreme temperature changes, and low soil moisture and nutrient conditions. An ecological restoration experiment was conducted using three site-preparation treatments, straw (S), Meri-Crusher (MC), and coarse woody debris (CWD), in a site-/no site-preparation 2 × 2 × 2 factorial on sites that had been barren for 25 years. In addition, four early successional deciduous species, white birch (WB, Betula papyrifera Marshall), gray birch (GB, Betula populifolia Marshall), green alder (GA, Alnus viridis Vill. subsp. crispa Ait), and speckled alder (SA, Alnus incana L. subsp. rugosa Du Roi), were examined. The two- and three-way interactions were almost all magnitude effects and not rank changes. Gray birch had the greatest overall first-year height growth, followed by GA, SA, and WB, with 12.1, 9.7, 9.6, and 5.6 cm, respectively. Straw doubled first-year growth, while CWD and MC increased first-year height growth by 43 and 31%, respectively. Straw’s ability to retain moisture in the dry summer provided the greatest benefit. In the second year, GA had the greatest height growth, followed by SA, GB, and WB, with 42.5, 30.5, 13.4, and 13.0 cm, respectively. Alders form symbiotic relationships with N-fixing bacteria and, although this was observed in some first-year roots, they did not fully express this advantage at these severely degraded sites until the second year, which allowed them to surpass birches in growth. Site-preparation treatments furthered their height growth affect, with S, and CWD doubling second-year height growth and MC, with an increase of 25%. Alders and birches had, on average, three and one stems, respectively, and the mean stem number of alders increased under S and CWD. After two years, overall stem dry mass had very large genus and species differences with GA, SA, GB, and WB, with 58.4, 30.3, 5.4, and 4.0 g, respectively. The N-fixing ability of alders under these conditions resulted in a 13-fold stem dry mass production increase compared with birches. Straw tripled, CWD doubled, and MC increased stem dry mass by 40%. For WB, site-preparation combinations had an additive effect, whereas GB, GA, and SA had several combined site-preparation treatments showing synergistic results, which were greater than the additive effects of single treatments. Under the control (no site prep.), second-year stem dry masses for WB, GB, GA, and SA were 0.7, 1.4, 17.8, and 0.5 g, respectively. Under the three combined treatments, MC × S × CWD, WB, GB, GA, and SA had 6.6, 12.3, 115.7, and 70.6 g stem dry masses, respectively. SA is ecologically a lowland species, hence the low 0.5 g under the control; however, the result under the three combined treatments demonstrates their combined effectiveness on these barren sites. Green alder seems to be the best adapted to the sites, having the greatest stem dry mass under control, although that was considerably magnified under the site-preparation treatments. This study using combinations of treatments with these early successional species introduces a novel research concept, and similar studies in the literature are currently lacking, creating an opportunity for future exploration. Full article

Atmospheric CO₂ levels have been increasing, and these changes may result in differential adaptive responses in both genera and species and highlight the need to increase carbon sequestration. Ecophysiological and morphological responses of four early-successional deciduous species were examined under ambient CO₂ (aCO₂, 400 ppm) and elevated CO₂ (eCO₂, 800 ppm) treatments. The four species, all of which are used in restoration, were Alnus viridis subsp. crispa (Ait.) Turrill (green alder), A. incana subsp. rugosa (Du Roi) R.T. Clausen (speckled alder), Betula populifolia (Marshall) (gray birch), and B. papyrifera (Marshall) (white birch); all are from the same phylogenetic family, Betulaceae. We examined biochemical efficiencies, gas exchange, chlorophyll fluorescence, chlorophyll concentrations, foliar nitrogen (N), and growth traits. A general linear model, analysis of variance, was used to analyze the functional carbon efficiency and growth differences, if any, among genera, species, and provenances (only for growth traits). The alders had greater biochemical efficiency traits than birches, and alders upregulated these traits, whereas birches mostly downregulated these traits in response to eCO₂. In response to eCO₂, assimilation either remained the same or was upregulated for alders but downregulated for birches. Stomatal conductance was downregulated for all four species in response to eCO₂. Intrinsic water use efficiency was greater for alders than for birches. Alders exhibited a consistent upregulation of stem dry mass and height growth, whereas birches were somewhat lower in height and stem dry mass in response to eCO₂. Foliar N played an important role in relation to ecophysiological traits and had significant effects relative to genus (alders > birches) and CO₂ (aCO₂ > eCO₂), and a significant genus × CO₂ interaction, with alders downregulating foliar N less than did birches. Covariate analysis examining carbon efficiency traits in relation to foliar N showed clear functional responses. Both species in both genera were consistent in their ecophysiological and morphological responses to CO₂ treatments. There was supporting evidence that assimilation was sink-driven, which is related to a plant organ’s ability to continue to grow and incorporate assimilates. The alders used in this study are actinorhizal, and the additional available foliar N, paired with increased stem dry mass sink activity, appeared to be driving upregulation of the carbon efficiencies and growth in response to eCO₂. Alders’ greater carbon efficiencies and carbon sequestration in impoverished soils demonstrate that alders, as opposed to birches, should be used to accelerate ecological restoration in a world of increasing atmospheric CO₂. Full article

Barren, severely disturbed sites lacking soil, such as mine sites and waste deposit sites, present severe challenges to ecological service restoration because of high temperatures, solar radiation, and wind speeds; extreme temperature changes; and low soil moisture and nutrient availability. An ecological restoration experiment using three site preparation treatments was conducted. Straw (S), Meri-Crusher (MC), and coarse woody debris (CWD) were assessed in a site, no site preparation 2 × 2 × 2 factorial, including a control treatment, on sites barren for 25 years. In addition, four early-successional species: white birch (WB, Betula papyrifera Marsh), gray birch (GB, Betula populifolia Marsh), green alder (GA, Alnus viridis Vill. ssp. crispa Ait) and speckled alder (SA, Alnus incana L. ssp. rugosa Du Roi), were examined for mortality. Mortality was measured after three time periods, summer-related 2021, winter-related, and frost heave mortality (spring 2022). Summer-related mortality was predominantly influenced by S treatments (reduced mortality) and their interactions. Straw’s ability to retain moisture strongly suggests it mitigated summer-related drought mortality. S interactions were not rank changes but magnitude effects. The species × straw interaction showed that SA had the greatest magnitude difference, with 25% and 3.6% summer-related mortality for NS and S treatments, respectively. SA, a hydrophilic species, accounted for nearly half the total summer-related mortality, and there were strong species effects and species interactions. The full combination of site preparation treatments had the lowest summer-related mortality, at 1%. Winter-related mortality only affected 1.9% of the total sample size, and there were no species effects or interactions, but contrary to other results, S was the leading cause of mortality due to fungal presence found on expired seedlings. For frost heave mortality, it was clear that the S treatment was effective, with 1.2% and 20.7% overall mortality for S and NS, respectively. MC alone had the greatest negative effect, with 46.9% frost heave mortality; however, when interacting with S or CWD, the mortality decreased substantially. Frost heave had no species interactions and only a species effect, with SA having the greatest mortality. Over the first full year, MC alone and control had the greatest mortality, with 60% and 38%, respectively, after one year. Overall, one-year mortality showed S reduced mortality by 27% and CWD by 19%, while MC increased mortality by approximately 4%. When treatments were combined in any way, mortality dropped significantly, showing an additive effect, with the three-combination treatment resulting in the lowest one-year mortality, of only 3.1%. Straw provided the strongest effect, both as an effective barrier to moisture evaporation, providing up to 10% more soil moisture under dry conditions and provided an effective thermal barrier that substantially reduced the frost heave mortality. Even early-successional species such as WB, GB, GA, and SA need site preparation treatments to establish and survive the first year on long-term barren lands. Full article

In boreal forests in Canada, broadleaf stands are characterized by generally well-drained soils and a humus-rich layer. In contrast, spruce-moss stands are often characterized by more poorly drained soils and acidic humus layer. However, presence of these two forest types in various degrees of mixture in stands can be beneficial to spruce seedlings productivity. It was hypothesized that leaf litter and humus from pure spruces-moss stands, pure broadleaf stands, and mixed stand may influence Black spruce (Picea mariana (Mill.) BSP) seedling growth and development differently. A greenhouse experiment was carried out to evaluate the effect of different leaf litter and different humus on spruces seedlings. Our results suggest better development for seedlings grown in humus from mixed stands and pure broadleaf stands compared to humus from pure B. spruce or standard forest nursery substrate. Furthermore, leaf litter from broadleaf trees species, such as species Speckle alder (Alnus rugosa (Du Roi) R.T. Clausen), T. aspen (Populus tremuloides Michx), Willows (Salix spp.) and Paper birch (Betula papyrifera Marsh.), has shown distinct results in the growth and development of B. spruce seedlings in greenhouse. Furthermore, promotion of mixed stand can increase B. spruce productivity by improving the physicochemical composition of the forest floor. Full article

Environmental concerns and economic pressures on forest ecosystems have led to the development of sustainable forest management practices. As a consequence, forest managers must evaluate the long-term effects of their management decisions on potential forest successional pathways. As changes in forest ecosystems occur very slowly, simulation models are logical and efficient tools to predict the patterns of forest growth and succession. However, as models are an imperfect representation of reality, it is desirable to evaluate them with historical long-term forest data. Using remeasured tree and stand data from three data sets from two ecoregions in northern Ontario, the succession gap model ZELIG-CFS was evaluated for mixed boreal forests composed of black spruce (Picea mariana [Mill.] B.S.P.), balsam fir (Abies balsamea [L.] Mill.), jack pine (Pinus banksiana L.), white spruce (Picea glauca [Moench] Voss), trembling aspen (Populus tremuloides Michx.), white birch (Betula papyrifera Marsh.), northern white cedar (Thuja occidentalis L.), American larch (Larix laricina [Du Roi] K. Koch), and balsam poplar (Populus balsamefera L.). The comparison of observed and predicted basal areas and stand densities indicated that ZELIG-CFS predicted the dynamics of most species consistently for periods varying between 5 and 57 simulation years. The patterns of forest succession observed in this study support gap phase dynamics at the plot scale and shade-tolerance complementarity hypotheses at the regional scale. Full article

Research Highlights: This research provides an application of a model assessing the naturalness of the forest ecosystem to demonstrate its capacity to assess either the deterioration or the rehabilitation of the ecosystem through different forest management scenarios. Background and Objectives: The model allows the assessment of the quality of ecosystems at the landscape level based on the condition of the forest and the proportion of different forest management practices to precisely characterize a given strategy. The present work aims to: (1) verify the capacity of the Naturalness Assessment Model to perform bi-directional assessments, allowing not only the evaluation of the deterioration of naturalness characteristics, but also its improvement related to enhanced ecological management or restoration strategies; (2) identify forest management strategies prone to improving ecosystem quality; (3) analyze the model’s capacity to summarize the effect of different practices along a single alteration gradient. Materials and Methods: The Naturalness Assessment Model was adapted to the Abies balsamea–Betula papyrifera forest of Quebec (Canada), and a naturalness assessment of two sectors with different historical management strategies was performed. Fictive forest management scenarios were evaluated using different mixes of forestry practices. The sensitivity of the reference data set used for the naturalness assessment has been evaluated by comparing the results using data from old management plans with those based on Quebec’s reference state registry. Results: The model makes it possible to identify forest management strategies capable of improving ecosystem quality compared to the current situation. The model’s most sensitive variables are regeneration process, dead wood, closed forest and cover type. Conclusions: In the Abies balsamea–Betula papyrifera forest, scenarios with enhanced protection and inclusion of irregular shelterwood cuttings could play an important role in improving ecosystem quality. Conversely, scenarios with short rotation (50 years) could lead to further degradation of the ecosystem quality. Full article

Research Highlights: Long-term exposure of paper birch to elevated carbon dioxide (CO₂) and ozone (O₃) modified metabolite content of over-wintering buds, but no evidence of reduced freezing tolerance was found. Background and Objectives: Atmospheric change may affect the metabolite composition of over-wintering buds and, in turn, impact growth onset and stress tolerance of perennial plant species in spring. Materials and Methods: Low molecular weight compounds of paper birch (Betula papyrifera) buds, including lipophilic, polar and phenolic compounds were analyzed, and freezing tolerance (FT) of the buds was determined prior to bud break after 11 growing seasons exposure of saplings to elevated concentrations of CO₂ (target concentration 560 µL L⁻¹) and O₃ (target concentration 1.5 × ambient) at the Aspen FACE (Free-Air CO₂ and O₃ Enrichment) facility. Results: The contents of lipophilic and phenolic compounds (but not polar compounds) were affected by elevated CO₂ and elevated O₃ in an interactive manner. Elevated O₃ reduced the content of lipids and increased that of phenolic compounds under ambient CO₂ by reallocating carbon from biosynthesis of terpenoids to that of phenolic acids. In comparison, elevated CO₂ had only a minor effect on lipophilic and polar compounds, but it increased the content of phenolic compounds under ambient O₃ by increasing the content of phenolic acids, while the content of flavonols was reduced. Conclusions: Based on the freezing test and metabolite data, there was no evidence of altered FT in the over-wintering buds. The impacts of the alterations of bud metabolite contents on the growth and defense responses of birches during early growth in spring need to be uncovered in future experiments. Full article

Moderate severity disturbances, which only kill a subset of canopy trees (e.g., via insects, pathogens, and windthrow), are increasingly widespread in North America, and can alter forest structure and production. Whether the net primary production (NPP) of forest stands differing in pre-disturbance site quality and composition respond similarly to moderate severity disturbance, however, is unknown, but critical to understanding the disturbance response dynamics of patchy landscapes. We experimentally disturbed three, 2-ha stands varying in pre-disturbance primary production and community composition, temporarily reducing live stand basal area by 38% to 66% through the stem girdling of all mature early successional aspen (Populus tremuloides Michx. and Populus grandidentata Michx.) and birch (Betula papyrifera Marshall). Disturbance significantly altered stand-scale physical and biological structure and prompted a similar decade-long pattern of wood NPP decline and recovery. All stands exhibited an initial reduction in wood NPP, followed by a recovery period and eventual return to pre-disturbance levels within eight years, with the most productive stand exhibiting an increase in primary production following recovery. Following wood NPP recovery, more biologically diverse forest canopies with higher leaf area indexes intercepted more light, and, consequently, had higher rates of wood NPP. We conclude that, despite substantial pre-disturbance differences in productivity and community composition, relative wood NPP recovery patterns can be similar, though long-term post-recovery primary production may trend higher in more productive and compositionally diverse stands. We suggest that improved mechanistic understanding of different forest ecosystems’ responses to disturbances remains critical to informing management decisions across diverse landscape mosaics. Full article

Well site development associated with oil sands exploration is common in boreal mixedwood forests of northern Alberta, Canada, and necessitates reforestation to accommodate other land uses. Little is known about the impact of soil and debris handling strategies during well site construction on long-term forest regeneration. This study addresses the impact of soil disturbance intensity, debris treatment, soil storage, and planting on the reforestation of 33 well sites reclaimed prior to 2006. Data on the survival and growth of planted white spruce (Picea glauca (Moench) Voss) and the regeneration density of deciduous trees, including trembling aspen (Populus tremuloides Michx), are presented from 2014 to 2015. The survival of planted spruce increased from 81% to 88% at well sites with a high relative to low soil disturbance. The total tree densities were lower in most treatments (≤2.69 stems m⁻²) than those in clear cuts (5.17 stems m⁻²), with the exception of root salvage areas where clear cuts had greater balsam poplar (Populus balsamifera L.) densities (2.05 stems m⁻² vs. <0.71 stems m⁻² on all other treatments). Aspen densities were up to five times greater at well sites with low disturbance when compared to those with high disturbance, and this was further aided by shallow mulch at low disturbance sites. Spruce growth did not respond to well site treatments. Aspen growth (diameter and height) remained similar between well site disturbance regimes; aspen exposed to high disturbance underperformed relative to low disturbance well sites and clear cut controls. With high disturbance, progressive soil piling led to increases in the density of aspen and birch (Betula papyrifera Marshall). Few long-term changes in soil were found due to well site development, with a greater soil pH in high disturbance sites compared to low disturbance sites. Overall, these results indicate that the nature of well site construction, including the extent of soil removal, soil piling, and debris treatment, may collectively alter forest re-establishment, with associated implications for forest management. Full article

This study presents the long-term (over the last 8000 years) natural variability of a portion of the Picea mariana-moss bioclimatic domain belonging to Québec’s Clay Belt. The landscapes are dominated by mesic-subhydric clay and early successional forests composed of Populus tremuloides, Pinus banksiana and Picea mariana. The natural variability (fires and vegetation) of one of these landscapes was reconstructed by means of pollen and macroscopic charcoal analysis of sedimentary archives from two peatlands in order to assess when and how such landscapes were formed. Following an initial afforestation period dominated by Picea (8000–6800 cal. Years BP), small and low-severity fires favored the development and maintenance of landscapes dominated by Picea and Abies balsamea during a long period (6800–1000 BP). Over the last 1000 years, fires have become more severe and covered a larger area. These fires initiated a recurrence dynamic of early successional stands maintained until today. A decline of Abies balsamea has occurred over the last centuries, while the pollen representation of Pinus banksiana has recently reached its highest abundance. We hypothesize that the fire regime of the last millennium could characterize Québec’s Clay Belt belonging to the western Picea mariana-moss and Abies balsamea-Betula papyrifera domains. Full article

Direct tree seeding is potentially an economical technique for restoring forests on abandoned fields. However, the success of tree establishment depends on many factors related to species and seed characteristics, environmental conditions, competition and predation. We compared seedling emergence, survival and growth of six tree species of different seed sizes in a forest restoration project of abandoned fields. Species were seeded in plots with and without herbaceous vegetation and with and without protection from bird and mammal predation. Yellow birch (Betula alleghaniensis) did not emerge in all treatments, paper birch (Betula papyrifera) and tamarack (Larix laricina) had a seedling emergence rate lower than 1%, and sugar maple (Acer saccharum) had a low overall emergence rate of 6%. Seedling emergence reached 57% for northern red oak (Quercus rubra) and 34% for red pine (Pinus resinosa), but survival of oak after one year was much higher (92%) than pine seedlings (16%). Overall, protection from birds and mammals and elimination of the herbaceous vegetation cover had no detectable effects on seedling emergence, survival and height. Nonetheless, red oak seedlings growing in the presence of vegetation had a smaller diameter and shoot biomass and a larger specific leaf area. We conclude that only large seeded species, such as oak, should be used for forest restoration of abandoned fields by direct seeding in our region. Full article