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Afforestation effects on SOC in former cropland: oak and spruce chronosequences resampled after 13 years
Author(s) -
Bárcena Teresa G.,
Gundersen Per,
Vesterdal Lars
Publication year - 2014
Publication title -
global change biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.146
H-Index - 255
eISSN - 1365-2486
pISSN - 1354-1013
DOI - 10.1111/gcb.12608
Subject(s) - chronosequence , subsoil , soil carbon , topsoil , environmental science , afforestation , basal area , carbon sequestration , forestry , soil science , agroforestry , ecology , soil water , geography , biology , carbon dioxide
Chronosequences are commonly used to assess soil organic carbon ( SOC ) sequestration after land‐use change, but SOC dynamics predicted by this space‐for‐time substitution approach have rarely been validated by resampling. We conducted a combined chronosequence/resampling study in a former cropland area (Vestskoven) afforested with oak ( Quercus robur ) and Norway spruce ( Picea abies ) over the past 40 years. The aims of this study were (i) to compare present and previous chronosequence trends in forest floor and top mineral soil (0–25 cm) C stocks; (ii) to compare chronosequence estimates with current rates of C stock change based on resampling at the stand level; (iii) to estimate SOC changes in the subsoil (25–50 cm); and (iv) to assess the influence of two tree species on SOC dynamics. The two chronosequence trajectories for forest floor C stocks revealed consistently higher rates of C sequestration in spruce than oak. The chronosequence trajectory was validated by resampling and current rates of forest floor C sequestration decreased with stand age. Chronosequence trends in topsoil SOC in 2011 did not differ significantly from those reported in 1998, however, there was a shift from a negative rate (1998: −0.3 Mg C ha −1 yr −1 ) to no change in 2011. In contrast SOC stocks in the subsoil increased with stand age, however, not significantly ( P = 0.1), suggesting different C dynamics in and below the former plough layer. Current rates of C change estimated by repeated sampling decreased with stand age in forest floors but increased in the topsoil. The contrasting temporal change in forest floor and mineral soil C sequestration rates indicate a shift in C source‐sink strength after approximately 40 years. We conclude that afforestation of former cropland within the temperate region may induce soil C loss during the first decades followed by a recovery phase of yet unknown duration.