[1] Katholieke Univ Leuven, Dept Earth & Environm Sci, Div Bioecon, Celestijnenlaan 200E, B-3001 Heverlee, Belgium
[2] Het Bolhuis, Asdonkstr 49, B-3294 Molenstede Diest, Belgium
[3] Katholieke Univ Leuven, Dept Earth & Environm Sci, Div Forest Nat & Landscape, Celestijnenlaan 200E, B-3001 Heverlee, Belgium