Soils developed on four parent materials (glaciolacustrine clay, clay loam till, coarse fluvial, and loamy eolian) in west-central Alberta were examined to determine residual effects of logging and use of site-preparation equipment upon soil bulk density. These studies were conducted on sites that were logged during the previous 24 years. Compaction was evident on all soils except those of the Summit association, which were dominantly Brunisolic Gray Luvisols developed on cobbly fluvial deposits of Tertiary age. Compaction was greatest on soils of the Marlboro association, which were dominantly Brunisolic Gray Luvisols developed on clay loam till. Soil bulk density values on the clear-cuts had recovered to those of the controls at comparable depth at ages ranging from 0 (Summit) to 17–21 years (Marlboro). Lodgepole pine and white spruce seedlings were grown on the four soils compacted in the laboratory to three bulk densities approximating the following field conditions: (1) those observed or expected immediately following logging and site preparation; (2) those observed 5–10 years after logging and site preparation; and (3) undisturbed control. In most cases, significant reduction in nine expressions of seedling growth (maximum root depth, maximum root depth in soil core, total weight, shoot weight, root weight, stem diameter, shoot height, seedling survival, and shoot weight: root weight ratio) was observed with increased bulk density.
Changes in climatic conditions may influence both forest biomass accumulation rates and natural disturbance regimes. While changes in biomass accumulation of forests under various climatic conditions have been described by yield equations, large uncertainties exist with regard to disturbance regimes. Under the doubling carbon dioxide scenario, global warming impacts have been predicted from simulation results of the first generation of coupled global climate model (CGCMI). The calculated fine fuel moisture code (FFMC) distribution from the simulation results showed a one-point increase compared with the distribution under current climate conditions. The impact of predicted changes in FFMC distributions on fire disturbance patterns, forest volume, and landscape structure was investigated by using the spatially explicit model for landscape dynamics (SEM-LAND). The simulation results showed increases in fire disturbance frequency and decreases in forest volume. The simulations also showed decreases in landscape fragmentation and landscape diversity, whereas total availability of core habitat for wildlife increased.
Effects of soil compaction and chipped aspen residue on aspen regeneration and soil nutrients. Can. J. Soil Sci. 78: 85-92. The effects of soil compaction and depth of chipped aspen residue on aspen regeneration, plant community development, decomposition, and nutrient cycling were tested on an Orthic Gray Luvisol in the Lower Foothills of Alberta. Twenty-seven 100-m × 15-m plots were established in 1992. Three depths of chipped aspen residue (0, 1-5 cm and >10 cm) and three levels of compaction (no compaction, 6 and 16 skidder passes) were applied following whole-tree harvesting in 1993. Sixteen skidder passes and chip residue depths >10 cm resulted in reduced plant cover and aspen sucker densities for at least 2 yr following treatment. Nutrient concentrations of the chip residue and surface organic horizon (LFH) were similar for the three compaction treatments. The initial total nitrogen (N) concentration of the chipped aspen residue was 3.6 g kg -1 . Ammonium (NH 4 + -N) concentrations in the LFH of the chip residue treatments, particularly at the >10-cm residue depth, were lower compared with the no-residue treatment. However, adequate N apparently was available to the aspen suckers and understory vegetation as the NH 4 + -N concentration remained higher than in the LFH before harvesting. Compaction and woody residue applications had only short-term (3 yr) effects on soil properties, plant community development and aspen suckering at this site when clear-cut harvesting was done in the fall with low soil moisture content.
The forests of the Wapiti map area, Alberta, were studied to ascertain relationships among forest growth, plant community distribution, and environmental factors within the western boreal and subalpine forests. Quantitative data on tree productivity, vegetation, and soils were collected from 137 plots. The 16 described forest community types (CTs) of predominantly fire origin were dominated by lodgepole pine (Pinuscontorta Dougl. var. latifolia Engelm.), white spruce (Piceaglauca (Moench) Voss), black spruce (Piceamariana (Mill.)B.S.P.), or aspen (Populustremuloides Michx.), were floristically simple (111 vascular plants), had tree productivity ranging from 0.4 m3 ha−1 year−1 in the Piceamariana/Ledumgroenlandicum/Rubuschamaemorus type to 5.0 m3 ha−1 year−1 in the Populusbalsamifera/Rosaacicularis/Thalictrumvenulosum type, and occurred on soils representing Luvisolic, Brunisolic, Gleysolic, Regosolic, Podzolic, and Organic orders. Two major successional trends are apparent in the upland boreal forest: lodgepole pine and aspen to the Piceaglauca/Rubuspubescens – Maianthemumcanadense type on moist sites at low elevations and lodgepole pine and black spruce forest to the Picea spp. – Abieslasiocarpa/Hylocomiumsplendens type on moist to well-drained sites at higher elevations. The Pinuscontorta/Menziesiaglabella/Rubuspedatus CT succeeds to the Piceaengelmanii – Abieslasiocarpa/Menziesiaglabella CT in closed canopy subalpine forests.
Tundra vegetation was analyzed on the basis of 64 sampled and 12 described stands representing a wide variety of plant community types immediately east of the Mackenzie Delta, Northwest Territories. Five main types (Tall Shrub – Herb, Medium Shrub (alder), Low Shrub – Heath, Herb – Low Shrub – Heath, and Herb) and 11 subgroups were distinguished and classified on the basis of floristic similarity using a two-dimensional ordination and by physiognomy. A total of 70 species were sampled or observed in the stands. Floristically, the Sedge–Cottongrass–Heath type was the most diverse and the Wet-Sedge Polygon – Herb type, the least diverse. The areal extent of each major community type was determined using aerial photography for Richards Island, Caribou Hills, Eskimo Lakes, Tuktoyaktuk, and Atkinson Point study areas.
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