TY - Generic T1 - Bark pH and susceptibility to toxic air pollutants as independent causes of changes in epiphytic lichen composition in space and time Y1 - 2001 A1 - van Herk, C. M. KW - agriculture KW - england KW - netherlands KW - pollution KW - quercus-petraea KW - vegetation JF - Lichenologist VL - 33 ER -