Chemical analyses
Total C and N-concentrations of soils (topsoil: 4 samples; subsoil: 1 composite sample from minimum 3 rings per site) and leaves (composite sample from ~30-50 leaves from minimum 7 trees per site) were measured in solid samples (soils: 7 mg, leaves: 5 mg) by Dumas combustion (1040 °C) on an elemental analyser (Eurovector CN analyser, Redevalle, Italy) after thorough homogenization in a ball-mill. Total P content was determined using a FIAstar 5000 flow injection analyser (FOSS, Hillerød, Denmark) on 25 mg samples, after total dissolution in H2SO4 with Se. Condensed tannin content was determined in 100 mg leaf material extracted in 5 ml methanol using the vanillin method with catechin as standard, and a Hitachi U 2010 spectrophotometer (Hitachi, Tokyo, Japan).