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Tree species selection in the design of agricultural riparian buffers is important to optimize particular ecosystem services, while vegetation management (weed treatment) is often critical in obtaining first-rate tree growth and survival. This farm-scale study took place along a 1 km section of a headwater stream in southern Québec (southeastern Canada). Five tree species with contrasted ecological characteristics were planted ( Populus × canadensis , Fraxinus pennsylvanica, Quercus macrocarpa , Quercus rubra and Pinus strobus ), with black plastic (polyethylene) mulches as the vegetation management method, as well as a control with no vegetation management, all within a fenced herbaceous riparian buffer. Tree growth and survival were measured along with soil nutrient supply. Significant Species × Vegetation treatment interactions where observed for all growth variables ( p < 0.001), but also for soil nitrate (NO 3 ) supply ( p < 0.01). All species benefited from the plastic mulch treatment, but varied greatly in their responses. After 5 years, mulched hybrid poplar produced 774 times more stem volume than red oak without mulch. Across all species/vegetation treatment combinations, a 13-fold variation in soil NO 3 supply rate was observed during the 4th growing season. Compared to the other species, NO 3 supply rate in hybrid poplar plots was 39–87% lower in the plastic mulch treatment and 48–62% lower in the control treatment. Significantly higher soil NO 3 supply rates were observed beneath the mulches of non nitrophilous species (white pine and red oak). Red oak growth was negatively correlated with NO 3 supply ( R 2 = 0.57, p < 0.05) in the mulch treatment. Early-successional nitrophilous species (hybrid poplar and red ash) planted with the plastic mulch led to the lowest increase in soil NO 3 and the greatest gains in buffer structural attributes (stem volume, diameter and height). Hybrid poplar growth was positively correlated with soil NO 3 supply ( R 2 = 0.86, p < 0.001) in the control treatment. Natural abandoned field/grassland invaders (white pine and bur oak) grew well without black plastic mulch, while the growth of non-mulched red oaks was marginal. In the control treatment, stem volume was a strong negative predictor (across all species) of soil NO 3 supply ( R 2 = 0.91, p < 0.05), indicating that under herbaceous vegetation competition larger trees have a greater ability to reduce soil NO 3 . This study provides evidence that particular tree species/vegetation management treatment combinations strongly influence early riparian buffer structural development and soil NO 3 dynamics in agricultural riparian zones. [ABSTRACT FROM AUTHOR]

We evaluated the extent to which general or site-specific allometric equations, using diameter at breast height (DBH) as a predictor, are more accurate for estimating stem volume, stem biomass, branch biomass, aboveground woody biomass, and coarse root biomass in 14 year-old plantations of Populus canadensis x Populus maximowiczii (clone DN x M-915508) located along an environmental gradient in southern Québec (eastern Canada). The effect of tree size and site on stem wood basic density, moisture content, and proportion of branch biomass was also evaluated. For stem volume, stem biomass, and aboveground biomass, site-specific and general models had comparable fit and accuracy, but lower Akaike's Information Criterion (AICc) values were observed for the general models. For the branch and coarse root biomass, higher fit and accuracy and lower AICc values were observed for the site-specific models. Allometric trajectory changes (plastic allometry) across sites were mainly observed for coarse root biomass, branch biomass, and stem volume. On the low fertility site, allocation was increased to coarse roots and decreased to stem volume. Site-specific tradeoffs between tree architecture and stem wood density explained the relatively invariant allometry for the whole aboveground woody biomass across the plantation sites. On the high fertility sites, basic wood density was the lowest and declined as tree DBH increased. At all sites, stem wood moisture content and the proportion of branch biomass increased with DBH. Overall, this study showed that biomass allometry, tree architecture, and biomass quality are a function of both tree size and plantation environment in hybrid poplar. Allometric model selection (site-specific or general) should depend on the objective pursued (evaluation of yield, nutrient budget, carbon stocks). [ABSTRACT FROM AUTHOR]

Invasive glossy buckthorn could reduce restoration potential for understory native forest herbs by compromising their growth and biodiversity. Few studies of glossy buckthorn's effects on forest herbs exist, and none were done in early-successional, partially open hardwood forests. This study was conducted in a mature hybrid poplar plantation invaded by buckthorn, located in southeastern Québec.We tested the effect of buckthorn removal on the growth of three forest herb species, whether this effect varied among species, and if canopy type (two poplar clones) influenced this effect. Forest herbs were planted in herbicide (buckthorn removed) and control treatments in the plantation understory, an environment similar to that of early-successional hardwood forests. Over the first two growing seasons, species showed specific reactions to buckthorn cover. Mean relative growth rate (RGR) for Asarum canadense and Polygonatum pubescens was increased in the herbicide treatment (48% and 33%, respectively) and decreased in the control treatment (--35% and --33%, respectively). Sanguinaria canadensis growth was the highest among species, with no difference between treatments. No effects of canopy type were detected. Results suggest that planting forest herbs for restoration purposes may be unsuccessful if buckthorn is present. Important changes in understory flora biodiversity are likely to occur over the long term in forests invaded by buckthorn. [ABSTRACT FROM AUTHOR]

In temperate agricultural watersheds, the rehabilitation of tree vegetation in degraded riparian zones can provide many ecosystem services. This study evaluated ecosystem service provision potential following the conversion of non-managed herbaceous buffers to hybrid poplar (Populus spp.) buffers in three watersheds (555-771 km²) of southern Québec (Canada), with contrasting agricultural land uses. To extrapolate services at the watershed level, total stream length where hybrid poplars could be established was calculated using GIS data from hydrological and land cover maps. After nine years, a 100% replacement of herbaceous buffers by hybrid poplar buffers along farm streams could lead to the production of 5280-76,151 tons of whole tree (stems + branches) biomass, which could heat 0.5-6.5 ha of greenhouses for nine years, with the potential of displacing 2-29 million litres of fuel oil. Alternatively, the production of 3887-56,135 tons of stem biomass (fuelwood) could heat 55-794 new farmhouses or 40-577 old farmhouses for nine years. Producing fuelwood in buffers rather than in farm woodlots could create forest conservation opportunities on 300-4553 ha. Replacing all herbaceous buffers by poplar buffers could provide potential storage of 2984-42,132 t C, 29-442 t N and 3-56 t P in plant biomass, if woody biomass is not harvested. The greatest potential for services provision was in the Pike River watershed where agriculture is the dominant land use. A review of the potential services of poplar buffers is made, and guidelines for managing services and disservices are provided. [ABSTRACT FROM AUTHOR]

Many small-scale private forest owners increasingly focus their management on amenity functions rather than on wood production functions. This paradigm shift is an opportunity to implement novel forestry management approaches, such as forested land zoning. Forest zoning consists in separating the land base in three zones that have different management objectives: (1) conservation zones; (2) ecosystem management zones; and (3) intensive production zones, which locally increase productivity, as a trade off to increase the land area dedicated to conservation and ecosystem management. We evaluate the ecological feasibility of implementing forest zoning on a private property (216 ha) at St-Benoît-du-Lac, Québec (Canada) characterised by agricultural and forest land uses. As a basis for delineating conservation and ecosystem management zones, historical and contemporary data and facts on forest composition and dynamics were reviewed, followed by a detailed forest vegetation analysis of forest communities. Delineating intensive production zones was straightforward, as fertile agricultural field margins located downslope were used to establish multifunctional hybrid poplar buffers. At St-Benoît-du-Lac, a realistic zoning scenario would consist of (1) conservation zones covering 25% of the forestland (37 ha); (2) ecosystem management zones covering 75% of the forestland (113 ha, including restoration zones on 24 ha); and (3) intensive production zones on 2.8 ha. Based on a yield projection of 13 t/ha/year for hybrid poplars, only 5.6% of agricultural field areas would need to be converted into agroforestry systems to allow for the loss of wood production in a conservation zone of 37 ha of forest. Ecosystem services provision following the implementation of zoning would include increased habitat quality, biodiversity protection and enhancement (by restoration of some tree species), carbon storage, non-point source aquatic pollution control, local biomass production for heating, and increased forest economic value. [ABSTRACT FROM AUTHOR]

The exotic shrub glossy buckthorn (Frangula alnus) is a great concern among forest managers because it invades both open and shaded environments. To evaluate if buckthorn grows similarly across light environments, and if adopting different shapes contributes to an efficient use of light, we compared buckthorns growing in an open field and in the understory of a mature hybrid poplar plantation. For a given age, the relationships describing aboveground biomass of buckthorns in the open field and in the plantation were not significantly different. However, we observed a significant difference between the diameter-height relationships in the two environments. These results suggest a change in buckthorn's architecture, depending on the light environment in which it grows. Buckthorn adopts either an arborescent shape under a tree canopy, or a shrubby shape in an open field, to optimally capture the light available. This architectural plasticity helps explain a similar invasion success for glossy buckthorn growing in both open and shaded environments, at least up to the canopy closure level of the plantation used for this study. [ABSTRACT FROM AUTHOR]

In this study, we developed clone-specific allometric relationships, with the objective of calculating volume and biomass production after 13 years in 8 poplar plantations, located across an environmental gradient, and composed of 5 unrelated hybrid poplar clones. Allometry was found to be very similar for clones MxB-915311, NxM-3729 and DNxM-915508, all having P. maximoviczii parentage. Clones DxN-3570 and TxD-3230 also had a similar allometry; for a given DBH they have a lower stem volume, stem biomass and branch biomass than P. maximoviczii hybrids. Strong Site × Clone interactions were observed for volume and woody biomass growth, with DxN and TxD hybrids only productive on low elevation fertile sites, whereas P. maximovizcii hybrids were also very productive on higher elevation sites with moderate to high soil fertility. At the site level (5 clones mean), yield reached 27.5 and 22.7 m3/ha/yr. on the two best sites (high fertility and low elevation), confirming the great potential of southern Québec (Canada) for poplar culture. The productivity gap between the most and least productive sites has widened from year 8 to year 13, highlighting the need for high quality abandoned farmland site selection in terms of climate and soil fertility. Although clone selection could optimize yield across the studied environmental gradient, it cannot fully compensate for inadequate site selection. [ABSTRACT FROM AUTHOR]

This study had three main objectives: (1) to evaluate the aboveground biomass and volume yield of three unrelated hybrid poplar clones in 9 year-old riparian buffer strips located on four farms of southern Québec, Canada; (2) to compare yield data at 9 years with previous data (at 6 years); (3) to evaluate how soil fertility, measured using three different soil testing methods (soil nutrient stocks, soil nutrient concentrations, soil nutrient supply rates), is related to yield. Across the four sites, hybrid poplar productivity after 9 years ranged from 116 to 450 m3ha-1, for stem wood volume, and from 51 to 193 megagrams per hectare (Mg ha-1), for woody dry biomass. High volume and woody dry biomass yields (26.3 to 49.9 m3ha-1yr-1, and 11.4 to 21.4 Mg ha-1yr-1) were observed at the three most productive sites. From year 6 to 9, relatively high yield increases (8.9-15.1 m3ha-1yr-1) were observed at all sites, but the productivity gap between the less fertile site and the three other sites was widened. Clone MxB-915311 was the most productive across the four sites, while clone DxN-3570 was the least productive. However, at the most productive site, clone MxB-915311 experienced severe stem and branch breakages. Independently of the soil testing method used, available soil P was always the first soil factor explaining volume yield. [ABSTRACT FROM AUTHOR]

Abstract: Multi-functional plantations using fast-growing tree species can potentially be used to accelerate the restoration of forest habitat on abandoned farmland. However, few studies have directly compared the ecological effects of active afforestation using plantations to natural afforestation. The present study compares the effects of the establishment and the first 10years of growth of two different hybrid poplar clones to adjacent abandoned fields and natural second-growth forests, in terms of abiotic attributes and understory vegetation communities. Experimental plantations of a Populus maximowiczii × P. balsamifera (M×B) hybrid and a P. deltoides × P. nigra (D×N) hybrid were established in 2000 on abandoned fields at 8 sites in southern Quebec, Canada. In 2009, soil chemical properties, soil moisture, canopy openness, leaf litter biomass, and understory vegetation communities were sampled in the plantations and in neighboring unmanaged abandoned fields and second-growth woodlots. Canopy development was greatly accelerated by the plantations of both hybrid poplar clones, compared to the unplanted portions of abandoned fields, and in the more productive plantations of both clones, canopy openness and leaf litter biomass were similar to those measured in the woodlots. No difference was detected in soil chemical properties between the abandoned fields and either type of plantation. The plantation soils were drier than those of both the abandoned fields and the secondary forests, possibly due to increased transpiration by the hybrid poplars. The plantations favored the colonization of the sites by native tree seedlings compared to the unmanaged fields, producing a nurse stand effect. Among herbaceous and shrub species, native species richness was slightly higher in the plantations than in the fields. The understories of the fastest growing plantations had species in common with both the fields and the woodlots, while the understory of the slowest growing plantations was very similar to the field vegetation. The plantation understories had lower covers of open-habitat species than the fields, while the M×B plantations had slightly greater covers of native, shade-tolerant species. Plantations of the M×B clone were more distinct from the abandoned fields than were plantations of the D×N clone. In conclusion, hybrid poplar plantations appear capable of accelerating the restoration of certain understory attributes, which in turn favors their colonization by tree seedlings and suppresses competition from light-demanding herbaceous species. [Copyright &y& Elsevier]

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Abstract: We evaluate, after 8 growing seasons, the effect of climate and soil characteristics on the biomass and volume yields of eight hybrid poplar plantations established on abandoned farmland sites, all planted during the same week, with the same five unrelated clones (D×N, T×D, N×M, DN×M, and M×B hybrids), and with the same silvicultural treatments. These plantations are located along an elevation (from 80 to 450m), or climatic gradient, but also along an edaphic gradient (from rich bottomlands to poorer hillside slopes). The largest effect that affected poplar volume yield was the Site effect (F ratio=134), followed by the Clone effect (F ratio=17), both effects being highly significant (p <0.001). However, a highly significant Site×Clone interaction suggests that the unrelated hybrid poplar clones used in this study respond differently to the environmental gradients. The large Site effect was expressed by hybrid poplar yield (5 clones mean) being as high as 22.4m3 ha−1 year−1 in the bottomlands of the Bedford site, where all clones reached their highest yield, and as low as 1.1m3 ha−1 year−1 on the poorer soils of hill slopes at Stornoway. Only one clone was the highest yielding at all sites, the N×M hybrid. The yield extremes observed highlight the strong control of elevation (proxy for climate), but also site fertility in terms of P availability on hybrid poplar productivity after 8years. Results from the stepwise regressions showed that Populus maximowiczii hybrids (N×M, DN×M, and M×B) productivity was first influenced by P availability followed by elevation, while D×N and T×D hybrids productivity was primarily influenced by elevation followed by P availability. Hybrid poplars related to the Tacamahaca section, and especially P. maximowiczii hybrids, were therefore able to produce relatively high yields (above 10m3 ha−1 year−1) on fertile sites located at higher elevation. In addition, simple regression models between elevation and productivity showed that the M×B hybrid, which has both of its parents from the Tacamahaca (balsam poplar) section, was the least influenced by elevation, an indication of its greater adaptation to colder climate. Because all clones strongly responded to soil P availability, clone selection cannot compensate for inadequate site selection in terms of soil fertility. Choosing high fertility abandoned farmland sites is therefore of paramount importance for hybrid poplar production. [Copyright &y& Elsevier]

In this field study, we used in vivo NRA activity in hybrid poplar leaves as an indicator of NO3- assimilation for five unrelated hybrid poplar clones. We also examined if leaf NRA of these clones is influenced to the same extent by different levels of soil NO3- availability in two riparian agroforestry systems located in pastures. Leaf NRA differences of more than one order of magnitude were observed between the clones, clearly showing their different abilities to reduce NO3 - in leaves. Clone DxN-3570, a P. deltoides x P. nigra hybrid (Aigeiros intrasectional hybrid), always had the highest leaf NRA during the field assays. This clone was also the only one to increase its leaf NRA with increasing NO3- soil availability, which resulted in a significant Site x Clone interaction and a positive relationship between soil NO3- concentration and NRA. All of the four other clones studied had one or both parental species from the Tacamahaca section. They had relatively low leaf NRA and they did not increase their leaf NRA when grown on the 3- rich site. These results provide evidence that NO3- assimilation in leaves varies widely among hybrid poplars of different parentages, suggesting potential preferences for N forms. [ABSTRACT FROM AUTHOR]

Linear bioenergy buffers planted with fast-growing trees along field edges are increasingly used to address challenges related to sustainable biomass production, climate change mitigation (i.e., carbon storage and microclimate regulation), water quality protection, and forest habitat connectivity in agricultural landscapes. This study assessed: (1) the extent to which 15 m wide hybrid poplar bioenergy buffers (1666 stems/ha) with closed canopy responded to thinning (diamond pattern of tree removal); (2) the regrowth of poplars from cut stumps following gap harvesting; (3) the effects of harvesting treatments on soil microclimate and nutrient availability; and (4) the spatiotemporal pattern of tree growth in unthinned plots. After three post-thinning years, results showed a strong growth response of seven-year-old hybrid poplar trees to thinning (12% increase in diameter and 30% increase in individual stem volume), accompanied by a slight decline in stand productivity. Gap harvesting was not an effective treatment to regenerate the stand from shoots growing from cut stumps because of the high deer browsing. Overall, thinning had marginal effects on soil nutrients and microclimate, compared with gap harvesting, which increased soil temperature, soil moisture, and the availability of several macro and micronutrients. However, harvest effects on soil nutrients were mostly observed during the first postharvest year, with the exception of soil nitrate, which was lowest in the gap treatment during the second postharvest year. Finally, the spatial pattern observed in tree growth between the buffer rows suggests that other more operational thinning patterns (row or corridor thinning) need to be evaluated in linear buffers. [ABSTRACT FROM AUTHOR]

Studies the possibility of growth of herbicide-free plantations of oaks and ashes along a gradient of open to forested mesic environments in southern Québec. Growth of hardwood species in herbicide-free mesic forested environments; Other conditions that affected the growth of different tree types; Effect of deer browsing on different oak and ash species.

Implementing bioenergy buffers on farmland using fast-growing tree species could reduce firewood harvest pressure in woodlots and increase forest connectivity, while improving carbon sequestration, phytoremediation, stream habitats, soil stabilization and hydrological regulation. The objective of the study was to evaluate the natural drying and chemical characteristics of hybrid poplar firewood produced from bioenergy buffers, and to compare these characteristics with those of native species harvested in adjacent woodlots. In Trial A, 110 cm-long unsplit logs (a feedstock for biomass furnaces) were produced to evaluate the effect of log diameter class on firewood quality. In this trial, hybrid poplar firewood characteristics were also compared with Populus tremuloides, Acer rubrum and Fraxinus americana. In Trial B, the effect of hybrid poplar genotype and cover treatment was evaluated on the moisture content of short split logs (40 cm long). Firewood of satisfactory quality was produced on a yearly cycle for short split logs, and on a biannual cycle for long unsplit logs. Covering short split log cords with metal sheeting lowered the final moisture content (from 20.7% to 17.3%) and reduced its variability, while genotype did not significantly affect final moisture content. In Trial A, larger-diameter logs from hybrid poplar had lower element concentrations, but slightly higher moisture content after two years. A two-fold variation in N concentration was observed between diameter classes, suggesting that burning larger poplar logs would minimize atmospheric N pollution. Heating value, carbon and calcium concentrations increased following the seasoning of hybrid poplar firewood. After the first seasoning year outdoors, hybrid poplar had the highest moisture content (33.1%) compared to native species (24.1–29.5%). However, after the second seasoning year in an unheated warehouse, the opposite was observed (14.3% for hybrid poplar vs. 15.0–21.5% for native species). Heating value, carbon and nitrogen concentrations were similar between tree species, while high phosphorus and base cation concentrations characterized hybrid poplar, suggesting higher ash production. Poplar bioenergy buffers could provide a complementary source of firewood for heating in the fall and in the spring, when the heat demand is lower than during cold winter months. [ABSTRACT FROM AUTHOR]

• Hybrid poplars are increasingly planted in multifunctional bioenergy buffers. • Small agroforestry systems are vulnerable to damage caused by deer overabundance. • Fencing increased stand biomass, energy content and C, N and P storage by 13–20%. • The genotype with a rough bark and low branch biomass was less affected by deer. • Larger planting stock types increased overall ecosystem services provision. Populus hybrids are increasingly planted in multifunctional bioenergy buffers bordering crop fields. However, such small agroforestry systems are vulnerable to damage caused by overabundant deer populations. We measured after 8 years the effects of white-tailed deer (Odocoileus virginianus), genotype and planting stock type on tree growth and ecosystem services provision (biomass production; energy, nutrient and carbon storage; and phytoaccumulation of soil nitrate and phosphorus) in 15-m wide buffers located downslopes of hayfields in southern Québec (Canada). Two deer protection treatments (fenced and unfenced), two genotypes (P. deltoides × P. nigra , genotype D×N-3570 and P. maximowiczii × P. balsamifera , genotype M×B-915311) and two stock types (bare-root stocks: ±1.8 m in height and whips: 2.5 m in height) were studied. In unfenced plots, deer heavily browsed poplars (increase in the height of the first branch by 59 cm), repeatedly rubbed tree bark (36% of trees with rubs for genotype D×N-3570, and 59% for genotype M×B-915311), slightly decreased survival (by 2.9%), which reduced tree-level and stand-level productivity. Proportion of trees with rubs, first branch height and survival were correlated (p < 0.001) with woody biomass yields. Fenced poplars increased wood volume, biomass and energetic content by 20–21%, and C, N and P stocks in aboveground biomass by 13–20%. Higher soil phosphorus bioavailability was also found in unfenced plots. Genotype D×N-3570, which allocates less biomass to branches, grows its first branches farther from the ground and rapidly develops a rough and thick bark, was the least affected by deer, despite its high palatability. Genotype M×B-915311, which had higher biomass allocation to branches, a smooth and thin bark, but low palatability, was the most affected by deer. Soils in plots of genotype M×B-915311 had the lowest macronutrients availability, except for nitrate. Biomass feedstock quality (i.e. low nutrient concentrations and high heating value of woody biomass) was highest for genotype M×B-915311. In both fenced and unfenced plots, whips were more productive than bare-root stocks, especially for genotype D×N-3570. Optimizing ecosystem services provision in bioenergy buffers can be achieved by fencing, and by genotype and stock type selection. [ABSTRACT FROM AUTHOR]

Bioenergy buffers planted with fast-growing woody crops such as hybrid poplars (Populus spp.) are increasingly integrated into agricultural land to enhance the provision of ecosystem services. Genotype and planting stock type selection may influence buffer establishment success and soil properties, which may affect buffer functions such as soil nutrient removal, hydrological regulation (i.e. soil dewatering) or local climate regulation (i.e. temperature reduction). This farm-scale study tested the effects of two unrelated hybrid poplar genotypes (P. deltoides × P. nigra, genotype D × N-3570 and P. maximowiczii × P. balsamifera , genotype M × B-915311) and two planting stock types (unrooted whips and bare-root stocks) on biomass growth, soil nutrient availability and soil microclimate in 15 m wide bioenergy buffers located downslope of hayfields in the cold temperate region of southern Québec, Canada. Poplar genotype had an important effect on biomass growth, soil microclimate and the supply rates of several macronutrients and micronutrients, while planting stock type had little effect on these variables. The P. maximowiczii × P. balsamifera genotype produced the highest biomass and had generally lower nutrient availability in the soil, but not for soil NO 3 , which was less available under the P. deltoides × P. nigra genotype. Compared to the hayfield soils, only the P. maximowiczii × P. balsamifera genotype maintained a lower supply rate of available P in the buffer soil. Compared to the hayfield soils, NH 4 supply rates were lower in the buffers for both genotypes, while NO 3 supply rates were similar or higher. Both genotypes had the capacity to maintain cooler soil temperatures and lower moisture content in the soil of the buffer compared to the adjacent hayfields, but this capacity was greater for the P. maximowiczii × P. balsamifera genotype. Because plant-soil interactions are strongly affected by hybrid poplar genetics, genotype selection is an important consideration in the design of multifunctional agricultural buffers. In temperate agroecosystems, future studies should try to identify productive poplar genotypes that would decrease topsoil NO 3 and P availability and reduce soil water content in order to minimize potential N and P losses from buffer soils during runoff events. • Hybrid poplar bioenergy buffers can improve ecosystem services provision on farmland. • Poplar genotype affects biomass growth, soil microclimate and nutrient availability. • Planting stock type had little effect on biomass growth and soil variables. • Buffer soils can have higher nitrate and phosphorus availability vs. hayfield soils. • Buffer soils had lower temperature and moisture content vs. hayfield soils. [ABSTRACT FROM AUTHOR]

This study took place in southern Québec (Canada) where young stands of white ash and grey birch have been underplanted with white pine, red oak, bitternut hickory and black walnut. The establishment success of white pine and red oak was measured with and without tree shelters (to protect from deer). Ecological factors affecting the height growth of the four species were also measured for protected trees. After 6 years, the survival and total height of unprotected oak was 29% and 44.3 cm vs. 80.5% and 138.5 cm for protected oak. White pine was less affected by browsing (survival of 79.5 and 93.5%; height of 138.5 and 217.9 cm for unprotected vs. protected pine). Height of white pine was higher in the grey birch stands, while height of all hardwoods was higher in the white ash stands, which had better soil drainage, higher fertility, and an understory dominated by Rubus species. Total height of all hardwoods was significantly (p < 0.05) correlated with Rubus cover and with soil fertility. Pine and walnut height were strongly correlated (p < 0.001) to shelterwood structure (canopy openness or total basal area). Pine was less sensitive to variations in shelterwood characteristics, while black walnut showed high sensitivity. This study provides evidence that underplanting is suitable for black walnut assisted migration northward and for bitternut hickory restoration, despite soil conditions that were less favorable than in bottomland habitats mainly supporting these species in eastern Canada. Tree shelters offering protection from deer browsing and species-specific site selection are recommended for underplanting in the southern Québec region. [ABSTRACT FROM AUTHOR]

In this study, planting density and site effects on hybrid poplar productivity and stem dimensions were evaluated on the mid-term and longer term (8 and 14 years) in southern Québec (Canada). We also evaluated the effects of planting density and site on biomass accumulation and carbon stocks in different plantation compartments, on biomass partitioning at the stand-level, on soil carbon stocks and on soil nutrient supply rate after 14 years. The experimental design consisted of three replicate poplar stands located along a site fertility gradient. Each stand contained six planting densities (ranging from 494 to 1975 trees/ha) and a single genotype (Populuscanadensis × P. maximowiczii hybrid). Planting density had a large effect on stem dimensions, but a minor effect on stand volume, aboveground woody biomass production, and aboveground biomass carbon stocks. Site selection and tree survival were more important factors affecting these variables. At all sites, and independent of planting density, mean annual volume increments were also higher after 14 vs. 8 years. On fertile sites, strong correlations between area per tree at planting and biomass partitioning, carbon allocation belowground, soil nutrient supply rate and soil carbon stocks were observed. Aboveground, higher competition for light with increasing planting density resulted in an increase in the stem to branch ratio. Belowground, higher competition for soil resources with increasing planting density reduced soil macronutrient availability (except for potassium), which likely stimulated carbon allocation belowground and carbon accumulation in the soil. Over the longer-term, higher density plantations of poplars could provide greater benefits in terms of carbon storage belowground (soil and roots). [ABSTRACT FROM AUTHOR]

This study was conducted in a riparian buffer bordering a 1 km segment of a headwater stream crossing a pasture site located in southern Québec (Canada). Three species were planted (black walnut (Juglans nigra L.), bur oak (Quercus macrocarpa Michx.), and eastern white pine (Pinus strobus L.)) with three vegetation treatments (control, herbicide (one application/year for 3 years), and black plastic mulch)). The main objective was to determine to which extent herbicide and plastic mulch, used with species having different ecological characteristics, affect tree growth and soil nutrient status in riparian buffers. Survival was high (>93%) for all species in all treatments. In the control (no vegetation treatment), growth was similar among species. Black walnut had the strongest growth response to herbicide and plastic mulch, and white pine had the weakest. For all species, growth was similar in the herbicide and the plastic mulch treatments. During the fifth growing season, plastic mulch increased soil nitrate and phosphorus compared to the herbicide treatment. In the plastic mulch treatment, higher soil nitrate supply was observed for species that preferentially uptake ammonium (black walnut and white pine). Soil nutrient supplies were similar between the control and herbicide treatments. Despite the more favorable nutritional conditions it provides, permanent black plastic mulching does not provide higher growth benefits after 5 years than a 3-year herbicide treatment. The high soil nitrate supply observed in mulched black walnut and mulched white pine may indicate a limited capacity for nitrate phytoremediation by these species. [ABSTRACT FROM AUTHOR]