peak solar influx plays an important role in the ecological energy budget (Pé wé , 1975; Van Cleve et al., 1992). This paper is the first to provide chemical, physical, and morphological properties of the soils in the boreal region of Alaska and To quantify soil development under contrasting slopeto demonstrate the dominant effect of landscape attributes in soil influenced energy regimes in a boreal setting, individual formation. This study was conducted to characterize soils and landsoil profiles must be characterized as catena sequences scape relationships in the boreal forest of Alaska. Sites representing on slopes of similar topography but different aspects. major landform positions and vegetation communities were selected The empirical data can be used to build a model of for study. Well-drained, shallow to moderately deep Inceptisols occur topographically influenced subsoil variability in boreal on the drier and warmer south aspect slopes with thin (5-9 cm) organic horizons and loamy textures. Poorly drained Gelisols form on wet regions strongly affected by fire and may also help preand cold north aspect slopes and valley floors with thick (18-52 cm) dict changes brought about by prescribed burning. organic horizons and permafrost within 45 to 60 cm of the surface. The Caribou-Poker Creek Research Watershed (CPC On the latter, mineral horizons are reduced. Soils on the ridgetop RW), located 50 km northwest of Fairbanks, Alaska show features of relic, nonsorted circle (a type of pattern grounds) (Fig. 1), is within the discontinuous permafrost zone that indicate a previous periglacial environment. The mineral soil on that extends across central Alaska eastward into northbackslopes is shallow to moderately deep due to gelifluction and slope movement but deep toward toeslopes. Charcoal particles, commonly central Canada. The watershed is representative of found within the soil profiles, attest to frequent fire events in the past. non-glaciated upland headwater stream basins found Fire has the greatest impact on soil properties on south aspect slopes throughout interior Alaska. Forest communities in the because the organic horizons are thin and dry, and easily destroyed by watershed are representative of the boreal forest zone fire. The underlying mineral horizons often develop hydrophobicity in Alaska. Forest fire is a dominant ecological factor in resulted from moderately and severe burn. Slope, aspect, and slope this region (Kasischke and Stocks, 2000) and there has gradient are major controlling factors for the contrasting soil types along the catena sequences in the watershed.

Fifty‐two soils under black spruce [Picea mariana (Mill.) Britton et al.]‐dominated forest communities were examined and assessed for their organic C (OC) stores in relation to soil characteristics. Study sites were located on a variety of parent materials, landscape positions, and drainage conditions. Results indicate that soils at most sites were weakly developed, commonly with organic (O) horizons ranging from 3 to 39 cm (≥100 cm occasionally). Organic C stores tended to increase as drainage changed from somewhat excessive and well to very poorly drained (average to 1 m: 12.6–50.9 kg OC m−2, respectively). The lowest OC store for an individual site was 7.1 kg OC m−2 in a well‐drained soil on an outwash plain and the highest was 109 kg C m−2 in a very poorly drained soil. Surface organic horizons contained 13 to 100% of the total pedon OC stores. In Gelisols, permafrost sequestered an average of 9, 19, and 39% of SOC stores for the somewhat poorly, poorly, and very poorly drained soils, respectively. The presence of permafrost in poorly drained sites increased average OC stores from 27.8 to 50.1 kg OC m−2 over those without permafrost. Soil bulk density, cation exchange capacity, and extractable acidity assessed in relation to OC stores of genetic horizons illustrate the significant impact of OC on soil properties. In previous ecological studies in Alaska, OC was determined for only the surface horizons; our data suggest that such shallow sampling may underestimate total OC stores by an average of 26% and up to 68%.

Fire has been the dominant disturbance in boreal America since the Pleistocene, resulting in a spatial mosaic in which the most fire occurs in the continental northwest. Spatial variation in snowshoe hare (Lepus americanus) density reflects the fire mosaic. Because fire initiates secondary forest succession, a fire mosaic creates variation in the abundance of early successional plants that snowshoe hares eat in winter, leading to geographic variation in hare density. We hypothesize that fire is the template for a geographic mosaic of natural selection: where fire is greatest and hares are most abundant, hare browsing has most strongly selected juvenile-phase woody plants for defense. We tested the hypothesis at multiple spatial scales using Alaska birch (Betula neoalaskana) and white birch (Betula papyrifera). We also examined five alternative hypotheses for geographic variation in antibrowsing defense. The fire-hare-defense hypothesis was supported at transcontinental, regional, and local scales; alternative hypotheses were rejected. Our results link transcontinental variation in species interactions to an abiotic environmental driver, fire. Intakes of defense toxins by Alaskan hares exceed those by Wisconsin hares, suggesting that the proposed selection mosaic may coincide with a geographic mosaic of coevolution.

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The general ecology of an undescribed indigenous earthworm species in the Megascolecidae, found in the organic horizons of Podzolic soils under mixed stands of Tsugaheterophylla, Abiesamabilis, Thujaplicata, and Pseudotsugamenziesii, is described. The earthworm is a member of the genus Arctiostrotus. Over a range of sites, population numbers of earthworms were correlated to rooting concentration in and immediately below the mor humus. By micromorphological examination, earthworm casts were found to account for up to 60% by volume of the constituent solids of the organic horizons. The abundance of both fine roots and fungal hyphae in the worm casts suggested high nutrient availability. Analysis of fresh faecal material showed a marked increase in most important nutrients (N, P, K, Mg, Fe, Na) relative to levels in noningested litter. Observations indicate that this earthworm species, whose population density may reach 200 m−2, has a major role in the decomposer subsystem of these ecosystems.