Forest management impact on soil organic carbon: A paired-plot study in primeval and managed European beech forests

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Forest soils have been recognized as important reservoirs of older stable carbon (C) in the biosphere and thus play a key role in the global C cycle. While much research has addressed the consequences of forest conversion and forest use on soil organic carbon (SOC) stocks, some controversies remain as to whether primary forest soils store significantly more SOC than soils in managed forests. Here, we explore the effect of forest management on SOC stocks in European beech (Fagus sylvatica) forests through a paired-plot study in nearby primeval and managed forests in the western Carpathians, testing the hypotheses that primeval forests store significantly more SOC especially in the topsoil and that larger biomass and deadwood amounts are important drivers. The three primeval forests stored on average 15 % more SOC (∼1.8 kg C m−2) in the organic layers and mineral soil to 50 cm depth than the managed forests prior to harvest (difference marginally significant at p = 0.09). Contrary to expectation, the difference was significant in the subsoil (30–50 cm depth) but not in the topsoil. Consequently, the primeval forests had a greater proportion of their SOC pool located in the subsoil than the managed forests. Despite considerably larger wood biomass and deadwood amounts in the primeval forests, SOC pools were neither related to biomass nor deadwood mass. PCA and correlation analyses revealed a prominent negative effect of the availability of Ca, Mg, K and P on SOC stocks, suggesting that clear-cutting has slightly (but significantly) increased nutrient supply in the managed forests, likely stimulating soil biological activity and reducing SOC storage in comparison to the primeval forests. We conclude that the primeval forest reference is important for assessing forest management effects on SOC storage, and that a long history of management likely has significantly reduced the SOC stocks of Central European beech forests.