The Forest Watershed and Riparian Disturbance (FORWARD) initiative integrates aquatic and soil science, hydrology, and forestry into models that link water quality, water quantity, and disturbance indicators with management of watersheds on the Boreal Plain of western Canada. The impacts of varying patterns and intensities of fire and logging are being evaluated for 16 streams in the Swan Hills, Alberta, with the intention to extend the approach to the eastern portion of the Boreal Plain and into the Boreal Shield. The study uses two comparative approaches: treatment versus reference stream and before versus after disturbance. Models generated will be applied to designated multi-user watersheds in selected forest areas. In addition to yielding transferable technology for forest product industries, the FORWARD study tests hypotheses related to effects of watershed disturbance on soils, hydrology, and water quality on the phosphorus-rich and fire-prone Boreal Forest in western Canada. Key words: watershed disturbance, surface waters, soils, hydrology, modelling, forest management.

Relationships between cation exchange capacity (CEC), clay and organic carbon contents and soil pH were analyzed by way of multiple regressions for upland soils in eastern Canada (mostly Ontario, with additional data for New Brunswick). This was done by vegetation type in an attempt to explain some of the otherwise unexplained CEC variations. Data were taken from about 2000 soil horizons (organic L, F, and H horizons as well as A, B, and C mineral soil horizons) under broadleaves (mostly maples, beech, birch or aspen as dominant species), conifers (mostly fir, spruces and/or pines), and grass vegetation. For the organic forest floor horizons (or L, F, and H horizons), both organic carbon content (%) and pH were highly significant for predicting CEC, i.e.,CEC (L, F, and H of broadleaves) = −38 + 0.71 × org. C (%) + 10.3 × pH (R2 = 0.69), andCEC (L, F and H of conifers) = −31 + 0.34 × org. C (%) + 12.1 × pH (R2 = 0.58).For the mineral soil, clay and organic carbon contents (%) and pH were highly significant for predicting CEC. Soils with forest vegetation were found to have lower contributions of organic matter to CEC than grassland soils, i.e.,CEC (forest soils) = −7.0 + 0.29 × clay (%) + 0.82 × org. C (%) + 1.4 × pH (R2 = 0.72),CEC (wooded grasslands) = −6.0 + 0.31 × clay (%) + 1.31 × org. C (%) + 1.0 pH (R2 = 0.74), andCEC (grasslands) = −8.3 + 0.24 × clay (%) + 2.14 × org. C (%) + 1.3 × pH (R2 = 0.79).Relationships that were developed from Ontario data for specific vegetational types (maple sites, strongly podzolized conifer sites, grasslands/croplands) were tested by comparing CEC predictions with reported values for similar sites in New Brunswick and Quebec. The predictions were consistent with the general trends for maple sites and grasslands/croplands, but CEC values were strongly overpredicted for Podzolic subsoils on conifer sites.Literature information of the CEC dependency on in situ pH is sparse. Existing information that is based on buffering grassland/cropland soil samples from pH 2.5 to 8 appears to mimic this dependency quite well. Key words: Cation exchange capacity, clay, organic carbon, soil pH, forests, grasslands

No abstract

(NHaOAc, were.determined for forest soil samples as follows: (1) before drying, and (2) at several time intervals after air-drvine (1, 5, 1l and 14 wk)' Values for CEC were obtained for the same samples by determining (1) the sum of cations (Aili,'Cu1i , Mg'* ,5*, Nu*' Fe3*' and Mn2*) in the extracts [denoted CEC(Dcations)NH,or" and CEClDcations)pso6l], and (2) the amount of ammonium retained by the soil samples against water-w1shi"g fa"".ii8a"c'ec(NHooAc) ano cgCir.IFrocl)]. The soils used in this investigation were taken from four New Brunswick upland'fbrest sites (two sular maple sites, one mixed wood site, and one spruce site)' It was found that (l) extractable Mg, K, Na, and Mn levels were gen"erally not affected by drying, storing,_and type of extractant; (2) For personal use only.

Mixedwood forests of white spruce ( Picea glauca (Moench) Voss) and trembling aspen ( Populus tremuloides Michx.) may possess ecological advantages over monospecific white spruce stands. Belowground competition may be reduced through vertically stratified roots; facilitation of growth may occur in upper soil layers through nutrient-rich trembling aspen litterfall. These effects may incentivize white spruce to preferentially exploit upper soil layers in mixedwood stands, resulting in wider root systems. This research contrasted white spruce fine root (diameter <2 mm) distributions in organic layers of white spruce and mixedwood stands. Research occurred at the Fallingsnow Ecosystem Project site in northwestern Ontario. Eighteen plots represented mixedwood and pure white spruce stands. Trees were mapped; foliage and root samples were collected. Roots were separated by species and scanned to determine length. Simple sequence repeat DNA profiles were determined for all white spruce trees and for 45 white spruce root fragments per plot. Root and tree DNA profiles were matched; corresponding distances were calculated. Most (80%) root fragments were within 3.2 m of tree stems. Root prevalence decreased rapidly with distance. Organic layer pH was significantly less acidic in mixedwood plots, but only in one block. A subtle significant trend towards wider root distributions occurred in mixedwood stands.