A large number of recent European studies report a significant forest soil acidification over the past 50 years. Soil acidification is a major cause of loss of soil buffering capacity and biodiversity. Soil acidification can be caused by several processes, of which atmospheric pollution is been considered to be very important. However, also tree species choice can be an important driver. The overall objective of this study is therefore to evaluate the effect of tree species induced soil acidification on litter and herb layer dynamics along a natural gradient of soil buffering capacity. Our study consists of three major parts. In a first observational part,  the magnitude and velocity of the effect of soil acidification on soil properties, litter layer, earthworm community and herbal biodiversity will be quantified. Secondly,  we aim to define threshold values for soil acidity of some forest herbs by means of a controlled pot experiment. Thirdly, we will test by means of a field experiment whether forest soils can recover from soil acidification.