Paul Sanborn

The Klondike goldfields and Pleistocene environments of Beringia

The Klondike goldfi elds of Yukon, Canada, contain a key record of Pleistocene Beringia, the region of Alaska, Siberia, and Yukon that remained largely unglaciated during the late Cenozoic. A concentration of mining exposures, with relict permafrost that is locally more than 700,000 years old, provides exceptional preservation of paleoenvironmental archives and a new perspective on the nature of paleoenvironments during the Pleistocene. A critical feature is the stratigraphic association of distal tephra beds with these paleoenvironmental archives, which facilitates their regional correlation and, in many cases, provides independent ages for the paleoenvironmental assemblages. Paleoenvironmental analyses of fossil arctic ground-squirrel middens and buried vegetation indicate the presence of cryoxerophilous (“steppe-tundra”) vegetation growing on well-drained substrates with deep active layers (seasonal thaw depths) during cold intervals of the Pleistocene. Studies of full-glacial paleosols and cryostratigraphic relations of associated ground ice indicate the importance of active loess deposition and surface vegetation cover in maintaining the functionally distinct mammoth-steppe biome, which supported grazing mega-fauna populations, including mammoth, horse,

Soil and sedimentary charcoal evidence for Holocene forest fires in an inland temperate rainforest, east-central British Columbia, Canada

Accelerator radiocarbon dating of 147 charcoal samples recovered from colluvial and alluvial fan deposits at 29 sites was used to reconstruct the Holocene fire history of an inland temperate rainforest watershed in east-central British Columbia (BC), Canada. Radiocarbon dates ranged from 182 to 9558 cal. yr BP, with prominent peaks in the probability distribution of calibrated dates at e. 7100, 3900, 2300, 1600 and 250-1000 cal. yr BP. The inferred median fire return interval (FRI) was 800-1200 cal. yr, depending on the extent of inbuilt age errors resulting from charring of wood pre-dating actual fire ages. This FRI is likely an overestimate, as less severe events may not have created sufficient erosion and slope instability to preserve a record of charcoal in buried soils and slope deposits. Median time since fire was 467 cal. yr based on ages of the uppermost charcoal found at each site, but the severity of heart-rots in the dominant redcedars (Thuja plicata Donn ex D. Don) prevented independent confirmation of stand ages by dendrochronology. Sites with multiple charcoal-containing layers having similar radiocarbon ages can be explained with reference to contemporary post-fire mass-wasting processes. Peaks in fire-related sedimentation probability coincided broadly with periods of higher fire frequency c. 600-1000, 1300-2400 and 3500-4500 cal. yr BP inferred from sedimentary charcoal records at subalpine sites in southwestern BC. Correspondence with fire records from more distant sites in northwestern North America was less clear.

Podzolic soils of Canada: Genesis, distribution, and classification

Sanborn, P., Lamontagne, L. and Hendershot, W. 2011. Podzolic soils of Canada : Genesis, distribution, and classification. Can. J. Soil Sci. 91: 843-880. Podzolic soils occupy 14.3% of the Canadian landmass, and occur in two widely separated areas, eastern Canada (northern Ontario, Quebec, Maritimes) and British Columbia, usually under coniferous forest and on non-calcareous parent materials. Broad climatic control of Podzol distribution and properties is evident at the national scale, with higher organic matter concentrations (Ferro-Humic Podzols) in wetter climates, in contrast to Humo-Ferric Podzols predominating in drier boreal forest regions. Humic Podzols are least abundant and are restricted to the wettest landscape positions. International and Canadian research suggests that a more diverse range of processes is involved in podzolization than was envisioned in the 1960s, and proposed mechanisms must account for observed patterns of organic matter distribution and a diverse array of inorganic amorphous constituents in profiles. Taxonomic concepts of Podzolic soils in the Canadian System of Soil Classification have remained consistent since the late 1970s, and the higher-level criteria defining the order and its great groups have proved to be meaningful in new applications, such as delineating soil carbon stocks across Canadian landscapes. Canadian contributions to pedological research on Podzols declined dramatically after 1990, coincident with shifting research priorities in soil science and diminished activity in soil survey.

Topographically controlled grassland soils in the Boreal Cordillera ecozone, northwestern Canada

Properties and ecological relationships of grassland soils were examined at three widely separated sites (Stikine River Valley, British Columbia, and Carmacks and Kluane Lake, Yukon) in the Boreal Cordillera ecozone of northwestern Canada. At these latitudes (58 to 62°N), grasslands are largely restricted to south-facing aspects, and usually occur as islands within the boreal forest. The grayish and yellowish brown, base-rich, Ah horizons had a thickness-weighted mean organic carbon concentration of 19.5 g kg-1. Ah horizons exhibited a range of microstructures similar to that documented in grassland soils in the southern Cordillera and Great Plains, ranging from spongy to massive in the young loess-derived Kluane Lake pedon to well-developed crumb microstructure in the finer-textured Stikine pedon. These pedons met the morphological and chemical criteria, and likely the soil climate requirements, for the Dark Brown and Brown great groups of the Chernozemic order of the Canadian System of Soil Classificati...

Effectiveness of five soil reclamation and reforestation techniques on oil and gas well sites in northeastern British Columbia

McConkey, T., Bulmer, C. and Sanborn, P. 2012. Effectiveness of five soil reclamation and reforestation techniques on oil and gas well sites in northeastern British Columbia. Can. J. Soil Sci. 92: 165-177. Techniques developed for forestry landing reclamation were applied to five oil and gas well sites in northeastern British Columbia to ameliorate soil and facilitate reforestation. Treatments implemented in fall 2003 and spring 2004 were tillage, wood chip mulch, tillage+wood chip mulch, tillage+incorporated wood chips, brush mats and a control. Lodgepole pine (Pinus contorta var. latifolia) and white spruce (Picea glauca) seedlings were planted. Soil and vegetation were assessed (bulk density, soil mechanical resistance, water content, air filled porosity, water retention, least limiting water range, nutrient availability, seedling survival and growth) throughout 2004 and 2005 growing seasons. Tillage improved soil physical condition, reducing soil mechanical resistance and bulk density; treatments did not affect soil chemical properties. Treatments did not significantly affect species survival; after 6 yr, spruce height and root collar diameter improved with tillage but treatments did not affect pine. Brush mats led to increased spruce growth. Regression relationships between tree performance and soil condition were significant, but generally did not explain large variability. More elaborate soil physical condition measures were no better than bulk density for predicting seedling performance, but relative bulk density and least limiting water range may be useful for evaluating soil productivity.

Genesis of upland soils, Lewes Plateau, central Yukon. Part 2: Soils formed in weathered granitic bedrock

Dampier, L., Sanborn, P., Smith, S., Bond, J. and Clague, J. J. 2011. Genesis of upland soils, Lewes Plateau, central Yukon. Part 2: Soils formed in weathered granitic bedrock. Can. J. Soil Sci. 91: 579-594. Polygenetic soils have formed on weathered granitic bedrock at high elevation (>1200 m asl) beyond the penultimate glacial limit on the Lewes Plateau in central Yukon Territory. Solum thickness in four Brunisols that were examined exceeds the depths of excavated pits (85-110 cm), but data indicate limited chemical weathering. Clay mineralogy is dominated by vermiculite and kaolinite. Smectite and chlorite are present in horizons derived, respectively, from residuum and colluvium. Sola are strongly cryoturbated, in spite of the lack of permafrost at these sites today. Three scenarios are proposed to explain these soils: preservation of relict soil features beneath cold-based ice, prolonged interglacial soil formation following erosion of till deposited by warm-based ice, and ice-free conditions throughout the Quaternary, with soil evolution shaped by multiple glacial-interglacial cycles.

Genesis of upland soils, Lewes Plateau, central Yukon. Part 1: Soils formed on Pleistocene glacial deposits

Dampier, L., Sanborn, P., Smith, S., Bond, J. and Clague, J. J. 2011. Genesis of upland soils, Lewes Plateau, central Yukon. Part 1: soils formed on Pleistocene glacial deposits. Can. J. Soil Sci. 91: 563-578. We describe and interpret nine upland (>1000 m asl) Dystric Brunisols and one Humo-Ferric Podzol formed on till of the McConnell [Marine Isotope Stage (MIS) 2] and penultimate (MIS 4 or 6) glaciations on the Lewes Plateau of central Yukon Territory. Unlike soils formed on correlative glacial deposits at lower elevation in the nearby Tintina Trench, the soils on the Lewes Plateau display only weak age-related differences. Penultimate and McConnell soils have solum thicknesses of 50-75 cm and <50 cm, respectively, but other morphological and chemical properties do not differ between the two age groups. Smectite is present in the McConnell soils; it was previously reported only in soils formed on Early Pleistocene glacial deposits in central Yukon and was interpreted to reflect weathering and soil formation during warm interglaciations. Paleoclimatic interpretations of clay mineralogy in central Yukon may be confounded by differences in parent material provenance and should be reassessed. This study shows that field soil characteristics alone are insufficient to differentiate McConnell and penultimate glacial deposits in upland landscape positions on the Lewes Plateau.

Genesis of Turbic Cryosols on north-facing slopes in a dissected, unglaciated landscape, west-central Yukon Territory

The characteristics and landscape distribution of Histic Dystric Turbic Cryosols were examined on a steep (>30%) northerly slope in the unglaciated Klondike Plateau, near Dawson City, Yukon Territory. Based on texture, major element geochemistry, and clay mineralogy, the mineral parent materials were crudely stratified, with a silty material of likely aeolian origin overlying sandy gravelly colluvium. Discontinuous organic matter-enriched horizons occurred 50 cm or more below the active layer, and contained abundant partially decomposed plant detritus. Eight accelerator radiocarbon dates, ranging from 350 ± 40 to 3680 ± 40 14C years BP, suggested that incorporation of organic materials within and below the active layer was geologically recent, and had likely occurred by a combination of cryoturbation and slope processes. The widespread and rapid initiation of mass movements on slopes containing permafrost that followed forest fires in 2004 on the Klondike Plateau may be an analogue for the processes that ...

Spatial and temporal modelling of aboveground carbon stocks using Landsat TM and ETM+ for a subboreal forest

Forest carbon (C) stocks and sequestration have become an important management consideration for countries with large forested regions. A series of Landsat Thematic Mapper (TM) images was obtained for the Aleza Lake Research Forest (ALRF) in subboreal British Columbia. Plot-based aboveground biomass and woody debris C stocks measured in 2003 and 2004 were related through regression analysis to TM and spatially explicit forest cover information. Two empirical models were developed, namely a biomass C regression model (BCRM) and a woody debris C regression model (WDCRM), with r2 values of 0.67 and 0.64, respectively. Uncertainties in C stock estimates were determined using a Monte Carlo uncertainty analysis. In 2003, the total C stocks in biomass and woody debris over the 6034 ha area were 588 ± 7 and 77 ± 2 kt, respectively. During the time period from 1992 to 2003, forest harvesting operations accounted for a loss of 39.9 ± 2.6 kt C, and remaining areas accounted for a gain of 31.3 ± 10.3 kt C. Therefore, there was a small and nonsignificant loss of 8.7 ± 10.6 kt C over this 11 year interval for the ALRF, implying that aboveground carbon stock losses associated with clearcuts were offset by carbon stock gains achieved through forest growth.