Spatial Patterning of Soil Carbon Storage Across Boreal Landscapes

The boreal forest covers 14% of the earth's vegetated surface but contains about 27% of the world's vegetation carbon and between 25% and 30% of the world's soil carbon. Unique features of this biome include cold climates, large areas of relatively flat topography, discontinuous permafrost, large and severe fire events, and the accumulation of peat.These characteristics are important in controlling energy and carbon cycling and either influence or are influenced by regional climate and hydrological regimes. Total carbon accumulation within an ecosystem reflects the balance between net primary production (NPP), decomposition, and nonrespiratory losses (dissolved carbon export, fire, and land-use changes). In this chapter, we use soil carbon storage as a long-term estimate of net ecosystem productivity (NEP; the balance between NPP and decomposition) and nonrespiratory losses that integrates annual variability in the ecosystem processes contributing to carbon balance. Our overall hypothesis is that a combination of regional and local physiography creates spatial heterogeneity in hydrology and soil temperatures. Hydrology and thermal regimes, in turn, influence distributions of fire, permafrost, peatlands, and vegetation and ultimately control long-term carbon storage in many boreal climatic zones. Soil carbon storage varies tremendously between boreal stand types or features and is particularly large in poorly drained peatland and permafrost ecosystems. Landscape composition, then, is important for scaling carbon storage in boreal regions. However, whether the configuration of upland and lowland ecosystems influences carbon processes has not been adequately explored but likely is important to variations in carbon emissions during fire. Biological controls such as herbivory and insect outbreaks are important to the distribution of plant species and nitrogen availability in forest ecosystems, but their influence on wetland systems or long-term carbon dynamics is not well understood.