The effects of anthropogenic nutrient addition and species combination on the growth and competitive abilities of four widespread foliose lichens was investigated using two replicated factorial nutrient addition experiments conducted in conjunction with field studies. The first was carried out on thallus fragments of P. caperata (Pc), P. saxatilis (Ps) and X. parietina (Xp) transplanted onto a saxicolous substrate (roofing slate). Thallus growth rates were dependent on lichen species (F=12.76; P<0.001) and application frequency (F=59.31; P<0.001) with low (xl) to medium (x2 & x4) applications significantly increasing growth (increase in final thallus diameter), compared with control treatments (no nutrients). At higher (x8 & xl6) applications a significant reduction in growth occurred compared with controls. Competition (number of thallus overlaps) was also dependent on both lichen species (F=5.62; P < 0.001) and application frequency (F=5.16; P < 0.001). All three species exhibited symmetrical competition under experimentally elevated nutrient conditions. In the second transplant experiment using P. caperata and P. reddenda (Pr), growth rates were again dependent on lichen species (F=8.31; P < 0.001) and application frequency (F=l 12.17; f <0.001). Both species exhibited symmetrical competition under experimentally elevated nutrient conditions. In the second transplant experiment using P. caperata and P. reddenda (Pr), growth rates were again dependent on lichen species (F=8.31; P<0.001) and application frequency (F=l 12.17; f <0.001). Both species exhibited symmetrical competition under experimentally elevated nutrient conditions. Field studies suggest asymmetrical competition occurs between P. caperata & X. parietina (Pc->Xp) where no experimentally elevated nutrient conditions exist. However, competition between P. caperata & P. saxatilis and P. saxatilis & X. parietina remains symmetrical (Pc<->Ps; Ps<->Xp). On beech, under conditions of no experimentally elevated nutrients, competition between P. reddenda and P. caperata was symmetrical (Pr->Pc). Furthermore there is evidence to suggest niche separation occurs between these two species and that this becomes less important under conditions of nutrient enhancement. These results suggest elevated nutrient levels alter growth rate and competition which affect lichen community structure.