Stevens CJ, Smart SM, Henrys PA, Maskell LC, Crowe A, Simkin J, Cheffings CM, Whitfield C, Gowing DJG, Rowe EC, et al. Terricolous lichens as indicators of nitrogen deposition: Evidence from national records. Ecological Indicators. 2012  ;20:196-203.

Stevens CJ, Smart SM, Henrys P, Maskell LC, Walker KJ, Preston CD, Crowe A, Rowe E, Gowing DJ, Emmett BA. Collation of evidence of nitrogen impacts on vegetation in relation to UK biodiversity objectives. JNCC; 2011.