Effects of sulphur dioxide and ozone on lichen colonization of conifers in the Liphook forest fumigation project

In the Liphook Forest Fumigation Project the conifers Picea abies (L.) Karst., P. sitchensis (Bong.) Carr. and Pinus sylvestris L, were grown from the seedling stage and subjected, by open-air fumigation, to three regimes of SO, (ambient, 4 ppb (parts in 10(9) by volume); low, 12 ppb; high, 20 ppb) and two regimes of O-3 (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. and Lecanora conizaeoides Nyl. 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 for P. abies and were scarcest on P. sylvestris which had the most acidic bark. E. prunastri was the rarest of the three lichens and only colonized plots exposed to ambient SO2 (4 ppb). Diminutive thalli of H. physodes were relatively numerous in the ambient SO2 plots, much scarcer in those receiving low SO2 (12 ppb) and rare in those with high SO2 (20 ppb). Coverage by L. conizaeoides was very low in the ambient SO2 plots but appreciable in the low and high SO2 treatment plots. The results indicate a directly beneficial effect of SO2 on L. conizaeoides colonization rather than an indirect benefit through competitor release. The O-3 treatment (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.