Root systems are crucial to tree and soil stability in terms of mechanical support, but are rarely considered in revegetation studies. This study aimed at determining the effect of planting density ...and herbaceous hydroseeding on the root architecture and mechanical resistance to uprooting of planted hybrid poplars on waste rock piles. The study took place at an open pit gold mine in the Canadian boreal zone where a hybrid poplar plantation was established in 2013 on soil-covered waste rock slopes (33%). Four treatments were randomly distributed in three replicated blocks: 4 × 4 m, 2 × 2 m, 1 × 1 m between trees and 2 × 2 m + h, corresponding to trees spaced at 2 × 2 m with hydroseeding. Lateral uprooting tests of four-year-old hybrid poplars were conducted in the direction of the slope. Maximum resistance to the uprooting force was observed in the 2 × 2 m treatment. Root systems were more symmetrical, deep, branched, and had higher root diameters in the 2 × 2 m and 4 × 4 m treatments. In contrast, the treatments with greater intra- or interspecific competition showed shallower, asymmetrical root systems with smaller roots. Therefore, competition significantly reduced tree anchorage. Les systèmes racinaires sont essentiels à la stabilité des arbres et du sol en termes de support mécanique, mais sont rarement considérés dans les études de végétalisation. Cette recherche visait à déterminer l'effet de la densité de plantation et de l'hydroensemencement herbacé sur l'architecture racinaire et la résistance mécanique au déracinement de peupliers hybrides plantés dans les pentes de stériles. L'étude a eu lieu à une mine d'or à ciel ouvert située dans la forêt boréale canadienne. Une plantation de peuplier hybride a été installée en 2013 sur des pentes de stériles recouvertes de sol (3 H:1 V), avec quatre traitements répartis au hasard en trois blocs de répétition: 4 × 4 m, 2 × 2 m et 1 × 1 m d'espacement entre les arbres, ainsi que 2 × 2 m + h correspondant à un espacement de 2 × 2 m avec hydroensemencement herbacé. Des tests d'arrachement latéraux de peupliers hybrides âgés de quatre ans ont été effectués dans le sens de la pente. La résistance maximale à la force d'arrachement a été observée pour le traitement de 2 × 2 m. Les systèmes racinaires étaient plus symétriques, profonds, ramifiés et avaient des diamètres racinaires plus élevés pour les traitements 2 × 2 m et 4 × 4 m. En revanche, les traitements avec une plus grande compétition intra- ou interspécifique ont montré des systèmes racinaires moins profonds, asymétriques et avec des racines plus petites. Par conséquent, la compétition a réduit considérablement l'ancrage des arbres.
Intra-clonal competition was studied in young hybrid poplar plantations to assess the effects of spacing on growth, biomass production and allocation, and morphological characteristics of above- and ...below-ground tree parts. Three spacings were used as whole-plots (1 × 1 m, 3 × 3 m and 5 × 5 m), with two hybrid poplar clones as subplots (BT747, Populus balsamifera L. × P. trichocarpa Torr. & Gray; MB915, P. maximowiczii A. Henry × P. balsamifera L.) in a split-plot design. After six growing seasons, diameter at breast height (dbh) increased by about 120% from the 1 × 1 m to the 5 × 5 m spacing for clone MB915, while there was no significant change in dbh for the other clone. The effect of spacing on height growth was opposite for the clones; it increased by about 175% from the narrowest to the widest spacing for clone MB915, while it decreased by about 27% for clone BT747. Estimates of above-ground biomass production after six growing seasons were significantly reduced with increasing spacing, with 29.6, 4.9 and 3.2 MgDM ha−1 on average from the narrowest to the widest spacing. Branch traits and the vertical distribution of leaf area were the most affected by spacing for both clones, while live crown ratio and percentage of syllepsis did not change. Spacing also affected proportions of biomass allocated to stem, leaves, and branches, but allocation to roots did not change.
The influence of forest ecology and strategic planning has increased in importance to support the management of mixed-species forests to enhance biodiversity. However, little is known about ...competitive and facilitative interactions between trees and species in mixed firâbeechâspruce forests, mostly because of a lack of long-term experimental research. In the 1960s, long-term sample plots were established in the Western Carpathians to develop region-specific yield models. Trees in the plots were measured at 5- to 16-year intervals from 1967(69). In 2010, the positions of standing trees in all plots were identified spatially. Stump positions were also identified to record the coordinates of trees that had been removed or had died. The objectives of this study were to evaluate the applicability of widely used competition indices for mature firâbeechâspruce mixed forests and to test whether the tree competition zone changes among species and forest stands of different stocking densities. Results showed that the best competition index was based on the comparison of the basal area of competitors and the subject tree in the radius, which was defined as a function of stand density and species. In addition, beech was found to be a strong self-competitor, which was not the case for silver fir (Abiesalba Mill.). Results suggest that simpler competition indices are better suited for such diverse forests, as more complex indices do not describe the competition interactions sufficiently well.
The Forest Resources Inventory provides the base layer to support decision-making for a variety of stakeholders in Ontario, Canada. The inventory is used to identify areas of high economic potential, ...endangered species habitat, and recreational opportunities. As technology evolves, the inventory creation process has changed. From fully manual efforts conducted in the era before planes or roads to hand-drawn sketches made aboard early aircraft, the early inventory program was designed to provide a rough context of timber availability. As society changed, more was asked of the inventory, and ecological and biological features were added. With a land area larger than many European countries to inventory, the creation of an accurate forest inventory in Ontario is a technological and logistical challenge. Although the acquisition technology and strategy have changed over time, the goal of providing an improved understanding into the extent and distribution of natural resources in the province of Ontario has not changed. This review aims to provide a comprehensive look at the history of these inventory efforts in Ontario, as well as provide some context for why the inventory contains the attributes it does today.
On mine waste rock slopes, trees with inadequate root development could be prone to uprooting. The anchorage of trees is mainly determined by the architecture of the root systems that drive their ...mechanical interactions with the soil. The objective of this study was to evaluate the effects of soil quality and of different planting materials on the architecture and resistance to shear stress of root systems of hybrid poplars four years after they were initially planted. The study was conducted in an open-pit-gold mine. A hybrid poplar plantation was established in 2013 on 33% soil-covered waste rock slopes, using a randomised complete block design, that is, 3 replicated blocks × 3 planting materials × 2 soil qualities. The stability of the hybrid poplars (resistance to uprooting) was evaluated using lateral traction tests. Complete excavations were performed to characterise their coarse root (>4 mm) architecture. Results showed no significant differences between treatments in terms of the maximum resistance force to uprooting, which varied between 7142 and 8989 N. After four growing seasons, no significant effects due to soil quality or planting material were observed in the number of lateral roots, mean root diameter, root biomass, aboveground biomass, and shoot/root ratio.
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.
Increasing the production of wood fibre from conifer species such as white spruce (Picea glauca (Moench) Voss) is one of many challenges in the management of boreal mixedwood forests. The effects of ...various competition measures on relative growth and relative growth rate variables were calculated for individual white spruce subject trees. Correlation analysis was used to explore relationships with competitor structural features, including the ratio of competitor basal area to subject tree basal area (CBAS), the ratio of competitor height to subject tree height (AHCS), and the proportion of softwood (FSW). Regression analysis was used to explore relationships with three distance-dependent competition indices. The ratio of subject tree height to diameter at breast height (DBH) (HDR), crown ratio (CR), and crown relative increment rate (CRIR) were significantly correlated with CBAS and AHCS. HDR, CR, CRIR, and DBH relative growth rate were all statistically significantly related to the competition indices. Results indicated that (i) relative growth and relative growth rate measures successfully captured a range of competition, (ii) crowns of trees with larger diameters used their horizontal growing space more efficiently to produce stemwood, and (iii) the proportion of softwood contributing to competition did not appear to influence subject tree production efficiency. Growth efficiency variables have the potential to improve our understanding of boreal mixedwood dynamics.
We report on a 60-year-old red pine (Pinus resinosa Aiton) spacing trial experiment located in Ontario, Canada, that included the combinations between six initial spacings (from 1.2 to 3.0 m) and the ...presence or absence of a commercial thinning (CT) regime, as well as their impacts on quadratic mean diameter (QMD) and stand volume yield. The CT regime, initiated at age 30, targeted a residual basal area (BA) of 38 m.sup.2 * ha.sup.-1 after each of four entries. Without thinning, as initial spacing increased, QMD increased; gross and net volume production peaked in the 2.1-2.4 m spacings. With thinning, similar trends with spacing were evident for QMD, although piece sizes were larger and differences between spacings were lower. The immediate increase of mean tree size caused by tree selection explained most of the differences in QMD between thinned and unthinned plots. Thinning to a common target BA resulted in similar standing volume across spacings. Cumulative gross yield was similar between spacings of <2.1 m for both thinned and unthinned stands and decreased for thinned plots for wider spacings. Greater net volume production in thinned stands with the narrower spacings confirmed that mortality was captured. Lower gross and net production for wider spacings suggested that thinning resulted in underutilized growing space.
Drought-induced tree mortality, which rapidly alters forest ecosystem composition, structure, and function, as well as the feedbacks between the biosphere and climate, has occurred worldwide over the ...past few decades, and is expected to increase pervasively as climate change progresses. The objectives of this review are to (1) highlight the likely ecological consequences of drought-induced tree mortality, (2) synthesize the hypotheses related to drought-induced tree mortality, (3) discuss the implications of current knowledge for modeling tree mortality processes under climate change, and (4) highlight future research needs. First, we emphasize the likely ecological consequences of tree mortality from ecosystem to biome to continental scales. We then document and criticize multiple non-exclusive tree mortality hypotheses (e.g., carbon starvation — carbon supply is less than carbon demand; and hydraulic failure — desiccation from failed water transport) from a more comprehensive ecological perspective. Next, we extend a forest decline concept model, Manion's framework, by considering new emerging environmental conditions, for a more thorough understanding of the effects of climate change on forest decline. We find that an increase in drought frequency and (or) climate-change-type droughts may trigger increased background tree mortality rates and severe forest dieback events, accelerating species turnover and ecological regime shifts. The contribution of CO2fertilization, rising temperature within the optimal growth range, and increased nitrogen deposition may defer or reduce this trend in tree mortality, but such contributions will vary between locations, species, and tree sizes. Multiple hypotheses proposed for drought-induced tree mortality are discussed, but coupling carbon and water cycles could help resolve the debate. The absence of a physiological understanding of tree mortality mechanisms limits the predictive ability of current models from stand-level process-based models to dynamic global vegetation models. We thus suggest that long-term observations, experiments, and models should be tightly interwoven during the research process to better forecast future climate changes and evaluate their impacts on forests.
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