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Abstract

Forest management and associated litter inputs and decomposition rates are thought to affect the carbon
storage in mineral soils. Here, we studied the effects of forest management on soil organic carbon (OC)
stocks in density fractions of Ah-horizons in soils that developed on loess. We used 82 beech (Fagus sylvatica
L.) dominated forest plots in Thuringia, Germany that differed in their management (unmanaged
forest, forests under age-class management and forests under selection cutting forest). After density fractionation
of the mineral soil with a 1.6 g cm3 polytungstate solution we determined OC concentrations
and stocks as well as CN-ratios in the free (f-LF) light fraction, the occluded (o-LF) light fraction and in the
mineral associated organic matter (MOM) fraction. In our study, Ah-horizons of beech forests stored on
average 2.6 ± 0.2 kg m2 (38.7 ± 1.3 kg m3) OC. The results showed that 37% of the bulk soil OC was
stored in the light fractions. We could show that OC stocks in the light fraction were significantly affected
by the amount of C stored in organic layers (p = 0.011). The OC stocks in the organic layers, in turn, were
higher in unmanaged forests and in forests under selection cutting. This suggests a sensitivity of unprotected
OC in the f-LF of beech forests against forest management. In contrast to the f-LF, the OC stocks in
the MOM fraction are mainly controlled by pedogenic properties such as clay and iron oxide content.
Even after several decades of forest management and with large sample size, an effect of forest management
on the stable MOM fraction could not be detected