Aspen ( Populus tremula), rowan (Sorbus auquparia) and sallow (Salix caprea) are deciduous tree species of low economic value for forestry and contribute to biodiversity of boreal forests. The species are rare in managed forest landscapes, and severely browsed by moose. Their recruitment needs to increase to meet requirements of sustainable forestry to factors that affect occurrence need to be indentified. Paper I is an exploratory study on distribution of these species in relation to natural and cultural factors. In paper II moose browsing on saplings, in young forests and the influence of the landscape at three spatial scales: stand (8.6 ± 0.8 SE ha), winter home range of moose (10 km2) and annual home range of moose (25 km2). Presence of these rare species was depending on a multitude of factors acting at different spatial scales. The most important variables were soil quality, successional stage, and ownership at the stand scale and area of deciduous forest at the landscape scale. Moreover, saplings occurred at low densities in young forests (paper II) and most interestingly, saplings occurred most in middle-aged forests (20-80 years) and less than expected in younger forests (<20y) (Paper I). Browsing intensity on the different species corresponded with moose food preference and annual home range scale was most relevant for understanding browsing. Browsing on rowan was highest where the volume of deciduous food and overall young forest area were low. Browsing on birch increased when pine volume and mean patch size of young forest increased, whereas browsing on aspen was negatively related to the same variables. Thus, my results strengthen the idea that food selection is a scale-dependent process and that trade-offs between food and cover may exist for moose. Moreover, I conclude that the presence of deciduous species was a result mainly of soil quality, forest management intensity, landscape context and that the distribution of food for moose at landscape scales similar to or larger than their home range may be useful for predicting browsing on the stand scale. I propose that deciduous forests may be valuable predictors of regeneration potential in the forested landscape, and that understory deciduous sapling in middle-aged forests may be important to promote restoration and conservation actions.

Natural regeneration is used to restock trembling aspen (Populus tremuloides Michx.) cutblocks and factors controlling regeneration are areas of interest and concern to the forest industry. Harvest operations in Manitoba require that coarse woody debris, or slash, be left and distributed in cutblocks. The objective of this study was to investigate the effects of slash loading on soil temperatures and aspen regeneration, and implications for harvest operations in the Duck Mountain area. Early sucker growth, initiation, and soil temperatures were surveyed in six winter and six summer cutblocks under different levels of slash loadings. A growth chamber study, using field temperature data as a guideline, examined the effects of diurnal temperature variation on sucker initiation and production. In winter and summer cutblocks, mean depths to sucker initiation from the parent root were 4.6 + 2.4 cm and 3.4 + 2.1 cm, respectively, and initiation of suckers occurred mainly from parental roots located in the LFH layer. Daily mean soil temperatures during the growing season were significantly lower under higher levels of slash (difference of 3.6 oC during May). Higher amounts of slash also significantly shortened the length of the growing season (89 fewer days above 0 oC in one season) and decreased the number of suckers produced (150 000 ha1 decreased to 14 000 ha-1), sucker volume (decreased by 256 cm3m-2) and leaf area index (decreased by 0.9). There was no difference in sucker production between any diurnal temperature treatments in the growth chamber study. Shallow depth to sucker initiation has important implications for harvest operations using heavy machinery especially those occurring during the summer season. Moderate levels of slash in summer cutblocks, and heavy levels of slash in winter cutblocks limit sucker growth. Although slash decreases diurnal temperature amplitudes, this may not be the reason for the decrease in sucker production associated with increased levels of slash. Both soil temperature and early sucker growth are strongly affected by slash loading; by monitoring harvest operations and the distribution of slash within cutblocks, the negative effect of heavy machine traffic and heavy piles of slash can be reduced and ensure successful forest regeneration.

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.

Natural regeneration is used to restock trembling aspen (Populus tremuloides Michx.) cutblocks and factors controlling regeneration are areas of interest and concern to the forest industry. Harvest operations in Manitoba require that coarse woody debris, or slash, be left and distributed in cutblocks. The objective of this study was to investigate the effects of slash loading on soil temperatures and aspen regeneration, and implications for harvest operations in the Duck Mountain area. Early sucker growth, initiation, and soil temperatures were surveyed in six winter and six summer cutblocks under different levels of slash loadings. A growth chamber study, using field temperature data as a guideline, examined the effects of diurnal temperature variation on sucker initiation and production. In winter and summer cutblocks, mean depths to sucker initiation from the parent root were 4.6 + 2.4 cm and 3.4 + 2.1 cm, respectively, and initiation of suckers occurred mainly from parental roots located in the LFH layer. Daily mean soil temperatures during the growing season were significantly lower under higher levels of slash (difference of 3.6 oC during May). Higher amounts of slash also significantly shortened the length of the growing season (89 fewer days above 0 oC in one season) and decreased the number of suckers produced (150 000 ha1 decreased to 14 000 ha-1), sucker volume (decreased by 256 cm3m-2) and leaf area index (decreased by 0.9). There was no difference in sucker production between any diurnal temperature treatments in the growth chamber study. Shallow depth to sucker initiation has important implications for harvest operations using heavy machinery especially those occurring during the summer season. Moderate levels of slash in summer cutblocks, and heavy levels of slash in winter cutblocks limit sucker growth. Although slash decreases diurnal temperature amplitudes, this may not be the reason for the decrease in sucker production associated with increased levels of slash. Both soil temperature and early sucker growth are strongly affected by slash loading; by monitoring harvest operations and the distribution of slash within cutblocks, the negative effect of heavy machine traffic and heavy piles of slash can be reduced and ensure successful forest regeneration.

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.

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Thesis (Ph. D.)--Institute of Paper Chemistry, 1952. / Includes bibliographical references (p. 117-119).