Intensive management of short rotation hybrid poplar (HP) plantations on agriculture land has demonstrated good early yields and promise as an alternative crop for farmers selling fibre to the forest industry. However, multiple rotations of HP may impact the future productivity of plantations through nutrient removals. The objectives, therefore, of this study were to determine the nutrient stores and fluxes for two HP plantations with differing site quality, fertilizer applications and past land management practices and to construct a 20-year nutrient budget to examine impacts of harvesting short rotation HP on long-term productivity.<p>Heights and biomass were measured by harvesting above- and below-ground and separating biomass into tree components; measurement of atmospheric deposition, mineral weathering, litterfall, litter decomposition, and leaching for HP plantations on an Alfalfa (HPA) and Pasture (HPP) sites in 2004-05. The budget was developed by averaging fluxes over 2 years and scaling up to a 20-year rotation. <p>Unfertilized treatments in the HPA plantation showed greater tree growth than all other treatments. Fertilized and unfertilized treatments had greater biomass production and nutrient pools than treatments at the HPP plantation. The fertilizer treatments did not affect on biomass production and nutrient accumulation.<p>Nutrient additions to the HPA were greater than the HPP plantations for leaf litterfall and leaching. Nutrient resorption from senescing leaves was greater at the HPP plantation suggesting that nutrient pools were smaller and that trees responded by keeping nutrients in the biomass. Fertilization at both plantations increased nutrient flow for inputs and outputs in 2004-05. Water leachate and leaf litterfall showed increased nutrient contents in fertilized treatments at both plantations.<p>A high fertility plantation that used fertilizer and practiced whole-tree harvesting exported more nutrients (and fibre) than a plantation with marginal site quality practicing stem-only harvesting. Time to replenish nutrients from atmospheric deposition and mineral weathering would range from 6 to 50 years for Ca and N, respectively, suggesting that subsequent plantations would require fertilizers to replenish soil nutrient reserves.<p>While HP plantations in Saskatchewan can produce high yields, they require large nutrient inputs and are inefficient (sequester a large amount) in nutrient use. High site quality is important to obtain high yields but conservational techniques, such as stem-only harvesting, are important in maintaining site quality over the long-term.

Intensive management of short rotation hybrid poplar (HP) plantations on agriculture land has demonstrated good early yields and promise as an alternative crop for farmers selling fibre to the forest industry. However, multiple rotations of HP may impact the future productivity of plantations through nutrient removals. The objectives, therefore, of this study were to determine the nutrient stores and fluxes for two HP plantations with differing site quality, fertilizer applications and past land management practices and to construct a 20-year nutrient budget to examine impacts of harvesting short rotation HP on long-term productivity.<p>Heights and biomass were measured by harvesting above- and below-ground and separating biomass into tree components; measurement of atmospheric deposition, mineral weathering, litterfall, litter decomposition, and leaching for HP plantations on an Alfalfa (HPA) and Pasture (HPP) sites in 2004-05. The budget was developed by averaging fluxes over 2 years and scaling up to a 20-year rotation. <p>Unfertilized treatments in the HPA plantation showed greater tree growth than all other treatments. Fertilized and unfertilized treatments had greater biomass production and nutrient pools than treatments at the HPP plantation. The fertilizer treatments did not affect on biomass production and nutrient accumulation.<p>Nutrient additions to the HPA were greater than the HPP plantations for leaf litterfall and leaching. Nutrient resorption from senescing leaves was greater at the HPP plantation suggesting that nutrient pools were smaller and that trees responded by keeping nutrients in the biomass. Fertilization at both plantations increased nutrient flow for inputs and outputs in 2004-05. Water leachate and leaf litterfall showed increased nutrient contents in fertilized treatments at both plantations.<p>A high fertility plantation that used fertilizer and practiced whole-tree harvesting exported more nutrients (and fibre) than a plantation with marginal site quality practicing stem-only harvesting. Time to replenish nutrients from atmospheric deposition and mineral weathering would range from 6 to 50 years for Ca and N, respectively, suggesting that subsequent plantations would require fertilizers to replenish soil nutrient reserves.<p>While HP plantations in Saskatchewan can produce high yields, they require large nutrient inputs and are inefficient (sequester a large amount) in nutrient use. High site quality is important to obtain high yields but conservational techniques, such as stem-only harvesting, are important in maintaining site quality over the long-term.

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In the continental United States, mean surface air temperature is expected to increase by up to 5°C within 100 years. With hotter temperatures, leaf budbreak is expected to occur earlier in forests, and leaf area is expected to increase in locations where temperature is limiting. The response of plant photosynthesis to hotter temperatures is less certain; plant productivity could increase or decrease. Past studies have found intraspecific variation in the responses of forest tree productivity, phenology, canopy leaf area, and leaf isoprene emission to warming, which all influence carbon uptake and yield for agricultural tree species; it is therefore important to understand not only how hot climates affect carbon uptake and biomass production between different tree species, but also in different genotypes of the same species. We conducted a common garden study at the Biosphere 2 research center near Oracle, AZ, USA. We created a hybrid poplar plantation of 168 trees, which were planted as cuttings in January 2013. The trees used in this study are comprised of 5 distinct genotypes of Populus deltoides × trichocarpa from a range of average annual air temperatures. We measured photosynthetic capacity, leaf phenological timing, canopy leaf area and aboveground woody biomass in 2014 growing season, and leaf isoprene emission in the 2015 growing season. We observed a strong effect of genotype on aboveground woody biomass increment, implying strong local adaptation to the home range and limited phenotypic plasticity in terms of physiological and biometric responses to high temperature environments. Our study suggests that genotypes from hotter home ranges are able to maintain photosynthetic capacity and canopy leaf area late into the growing season, despite high temperatures, and thus produce more aboveground woody biomass. This study may have implications for agricultural management—as temperatures warm where managers currently grow hybrid poplar for agricultural or other purposes, the genotypes from those home ranges would likely have reduced yield; managers could investigate the use of genotypes from home ranges with higher average temperatures to replace the vulnerable local varieties.

The increasing input costs for traditional agriculture has led land owners and producers in search of alternative opportunities to increase on-farm income. Replacing agricultural crops with short rotation woody species such as hybrid poplar trees is a form of agroforestry. The objectives of this project were to evaluate: 1) a suitable planting stock for hybrid poplar, 2) the effect of nitrogen (N) fertilizer application and pruning on hybrid poplar growth and, 3) the response of four hybrid poplar clones to fertilizer application and their suitability in the boreal transition ecoregion of Saskatchewan. <p>Two trials were established near Meadow Lake, Saskatchewan where three stock types (cuttings, root cuttings and rooted plugs) of Walker poplar were planted into former alfalfa and pasture fields. Trees were pruned each spring to remove multiple leaders and fertilized in year 2 with 100 kg N ha-1. The presence of roots on rooted cutting and plug stock types was beneficial in terms of hybrid poplar growth and survival. Trees grown from planting stock without roots had survival rates between 32-37% whereas, the survival of trees with roots at the time of planting ranged from 62-81% after two years of growth. Trees that were planted as a rooted stock were 3.5 to 4.2 times greater in height and 4.0 to 5.6 times greater in root collar diameter than trees planted as an un-rooted stock type. The application of fertilizer N decreased tree volumes by 31% at the Alfalfa site and had no effect on tree growth at the Pasture site. The total amount of fertilizer N recovered by the hybrid poplar trees ranged from 1-3% at the Alfalfa site and 3-5% at the Pasture site. <p>The second study involved planting four clones of hybrid poplar (Hill, Katepwa, Walker and WP-69) at the same two sites and applying fertilizer at rates of 0, 150 and 300 kg N ha-1 the first two years. Following the second growing season, Katepwa and WP-69 clones had the highest tree volumes of 750 and 1147 cm3 of the four clones evaluated. The Walker clone had the poorest survival rates (52-56%) compared to the other three clones (> 90% survival). Foliar N levels were not correlated with tree height at the Alfalfa (p=0.1326) or the Pasture (p=0.1063) sites. The relationship between foliar P concentration and tree height was more pronounced during July at the Alfalfa site with an r2 value of 0.7102. The N:P ratios for foliar tissue decreased with increasing fertilizer N application during August at the Alfalfa site. Foliar N:P ratios were the same among fertilizer and clone treatments at the Pasture site in August. <p>Results from this study suggest that rooted stock types increase the successful establishment of hybrid poplar plantations. However, application of N fertilizer may not increase growth of trees if soil N is adequate. Other soil nutrients need to be measured prior to fertilization to determine what nutrients may be limiting plant growth.

Site quality, or the ability of land to grow trees, is an important component for identifying the most appropriate locations for establishing plantations of fast growing tree species to meet societys demands for timber and other environmental benefits. The goal of this thesis project was to predict site quality for poplars using soil and site information in Saskatchewan, Alberta and Quebec and to examine the effect of site quality on competition control in hybrid poplar plantations in Saskatchewan.<p>The first study examined factors affecting trembling aspen productivity in the boreal shield ecozone of Quebec on till and fluvial parent materials using general map data and measured soil and site information. Relationships with productivity were stronger using measured soil and site variables for individual parent materials (R2>0.6) than using general map data only (R2<0.25). Including biological variables, such as overstory species composition, had a major impact on site quality with conifer dominance negatively impacting the growth of trembling aspen.<p>The second study examined the factors affecting trembling aspen productivity in the boreal transition ecoregion of Saskatchewan on three different soil parent materials: fluvial, lacustrine and till. Relationships with productivity were stronger using soil and site variables for individual parent materials (R2 0.48-0.58) than using agricultural capability classes or other soil properties for all plots combined (R2<0.2). For fluvial and lacustrine sites, increasing clay content and nutrient availability (e.g. pH and total N) were positively related to productivity while tree productivity was negatively related to poor drainage for till sites. <p>The third study examined the factors affecting site quality for a single hybrid poplar clone in industrial plantations in Alberta at both the local scale (between plantations) and the microsite scale (within plantations). At the local scale, foliar P and Cu concentrations, soil water availability and drainage, and Ca and Mn in the C horizon were related to hybrid poplar productivity. There were also curved relationships with productivity and soil texture in the B horizon and pH of the A horizon, indicating an optimal range for poplar growth. At the microsite scale, soil texture was the best predictor of productivity with different relationships at each site depending on where the sites were in relation to the optimal soil texture.<p>The final study examined the response of hybrid poplar plantations in Saskatchewan to interspecific competition control on a range of site productivities. Competition control greatly increased tree growth with the greatest benefit being on the best quality sites. Both water and nutrients were highly competed for between trees and weeds. In the weed-free plots, tree growth was positively related to the amount of silt and clay in the soil and foliar P concentrations. This series of studies has demonstrated that it should be possible to predict poplar productivity reasonably well using only soil and site information within limited areas across Canada. However, the important drivers of productivity varied between the regions studied and between site groupings, such as by parent material, within local areas. This information can now be used to help land managers make better decisions regarding the establishment and management of plantations of fast growing tree species, notably hybrid poplar plantations.

The increasing input costs for traditional agriculture has led land owners and producers in search of alternative opportunities to increase on-farm income. Replacing agricultural crops with short rotation woody species such as hybrid poplar trees is a form of agroforestry. The objectives of this project were to evaluate: 1) a suitable planting stock for hybrid poplar, 2) the effect of nitrogen (N) fertilizer application and pruning on hybrid poplar growth and, 3) the response of four hybrid poplar clones to fertilizer application and their suitability in the boreal transition ecoregion of Saskatchewan. <p>Two trials were established near Meadow Lake, Saskatchewan where three stock types (cuttings, root cuttings and rooted plugs) of Walker poplar were planted into former alfalfa and pasture fields. Trees were pruned each spring to remove multiple leaders and fertilized in year 2 with 100 kg N ha-1. The presence of roots on rooted cutting and plug stock types was beneficial in terms of hybrid poplar growth and survival. Trees grown from planting stock without roots had survival rates between 32-37% whereas, the survival of trees with roots at the time of planting ranged from 62-81% after two years of growth. Trees that were planted as a rooted stock were 3.5 to 4.2 times greater in height and 4.0 to 5.6 times greater in root collar diameter than trees planted as an un-rooted stock type. The application of fertilizer N decreased tree volumes by 31% at the Alfalfa site and had no effect on tree growth at the Pasture site. The total amount of fertilizer N recovered by the hybrid poplar trees ranged from 1-3% at the Alfalfa site and 3-5% at the Pasture site. <p>The second study involved planting four clones of hybrid poplar (Hill, Katepwa, Walker and WP-69) at the same two sites and applying fertilizer at rates of 0, 150 and 300 kg N ha-1 the first two years. Following the second growing season, Katepwa and WP-69 clones had the highest tree volumes of 750 and 1147 cm3 of the four clones evaluated. The Walker clone had the poorest survival rates (52-56%) compared to the other three clones (> 90% survival). Foliar N levels were not correlated with tree height at the Alfalfa (p=0.1326) or the Pasture (p=0.1063) sites. The relationship between foliar P concentration and tree height was more pronounced during July at the Alfalfa site with an r2 value of 0.7102. The N:P ratios for foliar tissue decreased with increasing fertilizer N application during August at the Alfalfa site. Foliar N:P ratios were the same among fertilizer and clone treatments at the Pasture site in August. <p>Results from this study suggest that rooted stock types increase the successful establishment of hybrid poplar plantations. However, application of N fertilizer may not increase growth of trees if soil N is adequate. Other soil nutrients need to be measured prior to fertilization to determine what nutrients may be limiting plant growth.

Site quality, or the ability of land to grow trees, is an important component for identifying the most appropriate locations for establishing plantations of fast growing tree species to meet societys demands for timber and other environmental benefits. The goal of this thesis project was to predict site quality for poplars using soil and site information in Saskatchewan, Alberta and Quebec and to examine the effect of site quality on competition control in hybrid poplar plantations in Saskatchewan.<p>The first study examined factors affecting trembling aspen productivity in the boreal shield ecozone of Quebec on till and fluvial parent materials using general map data and measured soil and site information. Relationships with productivity were stronger using measured soil and site variables for individual parent materials (R2>0.6) than using general map data only (R2<0.25). Including biological variables, such as overstory species composition, had a major impact on site quality with conifer dominance negatively impacting the growth of trembling aspen.<p>The second study examined the factors affecting trembling aspen productivity in the boreal transition ecoregion of Saskatchewan on three different soil parent materials: fluvial, lacustrine and till. Relationships with productivity were stronger using soil and site variables for individual parent materials (R2 0.48-0.58) than using agricultural capability classes or other soil properties for all plots combined (R2<0.2). For fluvial and lacustrine sites, increasing clay content and nutrient availability (e.g. pH and total N) were positively related to productivity while tree productivity was negatively related to poor drainage for till sites. <p>The third study examined the factors affecting site quality for a single hybrid poplar clone in industrial plantations in Alberta at both the local scale (between plantations) and the microsite scale (within plantations). At the local scale, foliar P and Cu concentrations, soil water availability and drainage, and Ca and Mn in the C horizon were related to hybrid poplar productivity. There were also curved relationships with productivity and soil texture in the B horizon and pH of the A horizon, indicating an optimal range for poplar growth. At the microsite scale, soil texture was the best predictor of productivity with different relationships at each site depending on where the sites were in relation to the optimal soil texture.<p>The final study examined the response of hybrid poplar plantations in Saskatchewan to interspecific competition control on a range of site productivities. Competition control greatly increased tree growth with the greatest benefit being on the best quality sites. Both water and nutrients were highly competed for between trees and weeds. In the weed-free plots, tree growth was positively related to the amount of silt and clay in the soil and foliar P concentrations. This series of studies has demonstrated that it should be possible to predict poplar productivity reasonably well using only soil and site information within limited areas across Canada. However, the important drivers of productivity varied between the regions studied and between site groupings, such as by parent material, within local areas. This information can now be used to help land managers make better decisions regarding the establishment and management of plantations of fast growing tree species, notably hybrid poplar plantations.

Trichloroethylene (TCE) was widely used as an industrial solvent and degreasing agent for most of the twentieth century. It is now a widespread groundwater contaminant. Phytoremediation may be a cost-effective cleanup method for TCEii contaminated soils and groundwater. Studies of environmental TCE fate are complicated by its volatility. The literature repons both significant and insignificant plant uptake of TCE. Conflicting findings may be due to differences in exposure level, conditions, and duration of the studies, or to experimental artifacts from laboratory systems. This research quantified plant uptake and volatilization of TCE using a unique laboratory system. Hybrid poplar trees were exposed to 1 or 10 ppm TCE over a 43-d period. [14C]TCE was added to four high-flow, aerated, hydroponic plant growth chamber systems designed to provide high mass recoveries, an optimal plant environment and complete separation between foliar and root uptake. Transpiration stream concentration factors (TSCFs) for TCE, calculated from total [14C]TCE in shoot tissues plus phytovolatilized 14C, were 0.11 for two 1 ppm treatments and 0.15 for a 10 ppm treatment with roughly 25% attributed to phytovolatilization. Though extending study duration from 26 to 43 d resulted in accumulation of more mass of 14C in plant tissues, it had no effect on TSCF. These TSCF values are much lower than other published experimental values and values predicted by a theoretical relationship between TSCF and octanol-water partition coefficient. The TCE metabolites trichloroethanol (TCEt), trichloroacetic acid (TCAA), and dichloroacetic acid (DCAA)were identified in plant tissues of the 10-mg/L treatment. Hybrid poplar uptake ofTCAA and TCEt was quantified using a simpler aerated hydroponic system. TSCF values were calculated based on extractable parent compound in shoot tiss ues. TSCF for TCEt was < 0.01. Presence of TCAA in hydroponic solution and in leaf and root tissues indicated transformation of TCEt to TCAA. TSCF for TCAA was < 0.03 and decreased with increasing exposure concentration. TSCF also decreased under oxygen-limited root-zone conditions. Presence of DCAA in leaf and root tissues indicated transformation ofTCAA to DCAA. Transformation of parent compound, coupled with low extractability, may contribute to low TSCFs.

Short rotation woody crops (SRWC) eastern cottonwood (Populus deltoides) and hybrid poplar plantations were established in 2021 in Pontotoc and Oktibbeha counties of Mississippi to study the biomass potential of SRWC for biofuel production. We used a novel backpack LiDAR system to measure forest metrics and harvested sample trees to build aboveground biomass (AGB) and leaf area index (LAI) equations. The results showed that LiDAR-derived variables accurately estimated aboveground biomass (R2 =0.81 and 29.22 % RMSE). However, the LAI estimation results showed that the LiDAR metrics moderately explained field measurements of LAI (R2 =0.31 and 18.05% RMSE) for individual-trees and poorly explained plot-level LAI measured with the LAI-2200C (R2 =0.11 and 66% RMSE). The backpack LiDAR system can be valuable for forest managers and researchers, enabling non-destructive AGB and LAI estimation. However, further research is required to overcome its limitations and achieve precise measurements of AGB and LAI.