1. Laboratory of Plant Ecology and Forest Botany, Forestry and Technology Centre of Catalonia, E‐25280 Solsona, Spain
2. Department of Botany, Faculty of Biological Sciences, University of South Bohemia, and Institute of Entomology, Czech Academy of Sciences, CZ‐370 05 Ceské Budejovice, Czech Republic; E‐mail
3. Agronomical Engineering School, University ofLleida, E‐25198 Lleida, Spain; E‐mail