The influence of changes in forest management over the past 200 years on present soil organic carbon stocks

Abstract

Forest ecosystems in Europe have been affected by human activities for many centuries. Here we investigate, if current forest soil organic carbon stocks are influenced not only by present ecological conditions and land use, but also by land management in the past. Based on the forest management history of the Hainich-Dün region a total of 130 inventory plots were selected in age-class forest and selectively cut forests under present management practice. The age-class forest originated from (1) former coppice-with-standards, (2) former selectively cut forests and (3) afforestation. The selectively cut forest contains “early regulated” forest where selective cutting has been practised for centuries, and forest, which was managed as coppice-with-standards through the 18th and the 19th centuries. We hypothesise that past management influences present soil organic carbon stocks. Density fractionation of soils in three physical fractions (HF: heavy fraction, o-LF: occluded light fraction, f-LF: free light fraction) was carried out to increase the probability of detecting long-lasting effects of management history. No detectable differences in soil organic carbon (SOC) stocks, as measured in kgm−2 ground area, of the mineral soil and the heavy fractions, were found between present and historical forest management types (average total organic carbon (OC) stocks of mineral soil: 9.7±2.3kgm−2; average OC stocks of the organic layer: 0.5±0.3kgm−2; average total inorganic carbon (IC) stocks of mineral soil: 5.0±3.7kgm−2). The variation of samples was overlapping. There was no consistent trend with management history. The upper mineral soil (0–30cm) contained about 74% of total SOC, with f-LF contributing 24% in 0–10cm and 20% in 10–30cm, and o-LF 9% in 0–10cm and 6% in 10–30cm. The HF contained 85% (0–10cm) and 86% (10–30cm) of SOC stocks in the bulk soil. There was a significant decrease of total SOC stocks in the 0–10 and 10–30cm depth increment with increasing abundance of beech. Mean 14C concentrations in the HF were 102.0 pMC in 0–10cm, and 93.4 pMC in 10–30cm, corresponding to a mean 14C age of around 100years and 550years, respectively. Modelling C-dynamics based on the present measurements reveals that disturbances depleting 50% of soil C-stocks would equilibrate after 80years. Thus, there is no memory effect of 19th century forest management. We conclude that past and present management has no detectable effect on present SOC.