Tree biomass does not correlate with soil carbon stocks in forest-tundra ecotones along a 1100 km latitudinal gradient in Norway

Due to climate warming, forests are expanding to higher elevations and
latitudes at the expense of tundra vegetation. While the subsequent
increase in aboveground biomass is well-documented, there is much
speculation regarding the effects on soil organic carbon (SOC) stocks. To
provide insight into the consequences of tree encroachment into treeless
tundra, we sampled SOC stocks across 36 forest-tundra ecotones along a
1100 km latitudinal gradient in Norway. Our results show that SOC stocks
vary greatly within, as well as among treeline ecotones, and that SOC
stocks do not correlate with tree biomass and tree species. SOC stocks do
increase with temperature, and vary with slope steepness, slope aspect,
and soil parent material. Applying a ‘space-for-time substitution’
perspective, our findings suggest that tree encroachment into tundra is
unlikely to have immediate consequences for SOC stocks.