Geochemical Versus Climatic Controls on Soil Organic Carbon
Description
We measured SOC and geochemical properties in surface (0 – 10 cm) mineral soil at 198 forested sites across the Boreal Plains, Boreal Shield, and Taiga Shield ecozones in central Canada. We expanded the analysis to include soils from temperate forests in the Mixedwood Plains ecozone of southeastern Canada as well as published data from natural shrublands and grassland.
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We sampled upland forest soils at 198 sites spanning Boreal (n = 183) and Taiga (n = 15) ecoregions in northern Saskatchewan, central Canada (Figure 1). Ecoregions are characterized by distinctive regional ecological factors, including climate, physiography, vegetation, soil, water, and fauna. To achieve appropriate geographical coverage, soils were sampled from at least three ecodistricts within each ecozone, however, site selection was also influenced by accessibility (primarily by road in the south, and fixed-wing aircraft in the north). An ecodistrict is a subdivision of an ecoregion and is characterized by distinctive assemblages of relief, landforms, geology, soil, vegetation, water bodies and fauna. At each site, a single pit was excavated, horizon depths were measured, and composite soil samples from multiple faces of the pit were collected by horizon from the rooting zone and subsoil (Whitfield & Watmough, 2012). Samples were stored in coolers for transport to the laboratory. Here our analysis focuses only on the uppermost mineral soil horizon (0 – 10 cm) for each site. Long-term annual air temperature and precipitation for forested sites in the Boreal region were available from Environment Canada’s gridded (GEM) climate normals. The analysis was extended beyond Saskatchewan using available datasets for Mixedwood sites in Ontario, Canada (Ontario Forest Biomonitoring Network) (Koseva et al., 2010) and shrub and grassland sites in Chile and the Antarctic peninsula (Doetterl et al., 2015). Long-term modelled terrestrial NPP data (2001–2023) for all sites were extracted (package: ‘modisfast’) (Taconet & Moiroux, 2024) from the National Aeronautics and Space Administration’s Moderate Resolution Imaging Spectroradiometer dataset (Running et al., 2015) through spatial data analysis of sample point coordinates (latitude and longitude values). In select cases (e.g., for sites near the shore of larger lakes), terrestrial NPP data were not available.
Institutions
- University of Saskatchewan
- Trent University