@article{FranzenReuterStapper2004,
  author    = {Isabelle Franzen-Reuter and N. J. Stapper},
  title     = {Mapping aerial hypertrophication with epiphytic lichens as biomonitors in North Rhine-Westphalia (NRW, Germany)},
  journal   = {English Nature Research Reports. Lichens in a changing pollution environment},
  volume    = {525},
  pages     = {31 -- 36},
  year      = {2004},
}