Digital Soil Mapping in a Hypermaritime Forested Watershed: British Coumbia.

To support ecological and hydrological research in the ca. 7000 hectares of the watersheds feeding into Kwakshua Channel on Calvert and Hecate islands, a digital soil mapping program was undertaken in spring 2015.  This complex soil landscape consists of a mosaic of dense and open forests, along with sloping bogs and organic soils interspersed with rocky outcrops. Evidence for lateral fluxes of materials through shallow, sloping soils, as well as widespread occurrence of cemented horizons was observed during the field sampling.  Using existing terrestrial ecosystem mapping (TEM) as a guide, field data collection was carried out at 194 points, collecting basic information on soil and site characteristics (depth to bedrock, organic horizon thickness, material type, and soil classification).  A spatial database of 50 attributes was prepared for all observation points. We used training data collected during field sampling, as well as other sources of information such as a high-resolution digital elevation model (DEM), terrestrial ecosystem mapping, and digital aerial photography to carry out spatial modeling of ecosystem classes and soil attributes with random forest. Predictions were then coalesced into summaries of organic and mineral soil thickness for each of seven sub-basins in the study area. Organic horizon thickness ranged from 0 to more than 200 cm, with about 60% of the points having more than 25 cm of organic material at the surface. Mineral soil materials, including morainal, colluvial and fluvial material, dominated the surface layers at 10% of the points, while bedrock outcrops covered 5% of the area.