Effects of sulphur dioxide and ozone on lichen colonization of conifers in the Liphook Forest Fumigation Project

summary In the Liphook Forest Fumigation Project the conifersPicea abies(L.)Karst.,P, sitchensis(Bong‐) Carr. andPinus sylvestrisL. were grown from the seedling stage and subjected, by open‐air fumigation, to three regimes of SO2(ambient, 4 ppb (parts in 109by volume); low, 12 ppb; high, 20 ppb) and two regimes of O3(ambient, 25 ppb; high, 30 ppb) in factorial combination, between 1987 and 1990. We determined the abundance of three lichens,Evernia prunastri(L.) Ach.,Hypogymnia physodes(L.) Nyl. andLecanora canizaeoidesNyl. ex Crombie, which colonized the trunks and branches of the saplings, at the end of the experiment between May‐July 1991. All three species showed a marked preference forP. abiesand were scarcest onP, sylvestriswhich had the most acidic hark.E. prunastriwas the rarest of the three lichens and only colonized plots exposed to ambient SO2(4 ppb). Diminutive thalli ofH. physodeswere relatively numerous in the ambient SO2, plots, much scarcer in those receiving low SO2(12 ppb) and rare in those with high SO2(20 ppbl. Coverage byL. conizaeoideswasverylow in the ambient SO2, plots but appreciable in the low and high SO2treatment plots. The results indicate directly beneficial effect of SO2onL. conizaeoidescolonization rather than an indirect benefit through competitor release. The O3treatment (1.3 times ambient during Spring‐Autumn) did not influence the abundance of the lichens. All three lichen species appeared to be more sensitive (positive and negative effects) to SO2, than mapping studies have suggested. Possible reasons for the high SO2‐sensitivity of the lichens are discussed. These include the high acidity of conifer bark and the fact that growth from diaspores and development of immature thalli is involved rather than survival of established populations.