“Free air” ozone canopy fumigation in an old-growth mixed forest: Concept and Observations in Beech. - Nunn,A..J..; Reiter,I..M..; Häberle,K..H..; Werner,H..; Langebartels.,C..; Sandermann,H..; Heerdt,C..; Fabian,P..; Matyssek,R.. (Phyton, 2002)