The objective of this study was to compare the accumulation over time of organic carbon (C) in soil and vegetation of abandoned agricultural lands left to natural vegetation succession or afforested with planted white spruce (Picea glauca (Moench) Voss) in Abitibi (Canada). The agricultural areas of this region originated from the clearing of forested lands in the late 19th -early 20th centuries. The aim was to determine whether afforestation of such lands is a relevant tool for C sequestration and climate change mitigation.
Field and laboratory measures for tree, shrub and herbaceous strata, woody debris and soil down to a 50 cm depth were carried out on abandoned agricultural lands that were either left to natural succession or planted, to determine total C stocks. The experimental design was a chronosequence covering 50 years, with sites representing various stages following agriculture abandonment and plantation.
There was no significant difference in the amount of C stored by lands that were either planted or left to natural succession over a 50-year time period. Both types of lands were found to be net C sinks. Abandoned lands left to natural succession stored 1.3 times more C in the soil compared with afforested lands, while the latter stored twice as much C in aboveground biomass.
These results put into perspective the use of afforestation to increase land C sinks and suggest that natural succession might also play a role in land management practices in the context of climate change mitigation.