Long-term effects of historical heathland farming on soil properties of forest ecosystems

Abstract

Much of Europe's landscape has been converted from agricultural land to forest over the last 150 years. Previous land-use activities may have persistent effects on forest ecosystem properties, yet there is scant information on the long-term recovery of forest soils from agriculture. In this study we examined the effects of historical heathland farming on forest soil properties by comparing (i) ancient oak forests with oak stands afforested more than 115 years ago on (ii) former heaths and (iii) formerly cultivated fields in NW Germany. Our results showed that former fields had significantly lower C, N, and P stores and lower C/N- and C/P-ratios in the organic layer than former heaths and ancient oak forests, but revealed more plant-available P, higher total P contents and low C/P-ratios in the A-horizon. We concluded that higher plant-available P and P stores in the A-horizon reflected well the former manuring of fields, while lower C, N, and P stores in the O-horizon were related to the age of the forest floor. Differences between former heaths and ancient forests were less pronounced and characterized by a low base saturation (BS) and high C/N-ratio in the organic layer of ancient forests, attributable to nutrient sequestration in forest biomass and to changes in microbial communities, respectively. In our study, organic layer and A-horizon served as complementary tracers for land-use legacies, since some of the effects of historical heathland farming were only detectable by means of properties of one of the humus horizons. Our findings demonstrate that heathland farming needs to be considered as a “historical site factor” when analysing forest ecosystem processes, since soil legacies resulting from heathland farming may still impact present-day patterns of biodiversity and tree growth in lowland forest ecosystems.