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 SO₂ (ambient, 4 ppb (parts in 10⁹ by 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. and Lecanora canizaeoides 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 hark. 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 ppbl. 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 directly beneficial effect of SO₂ on L. conizaeoides colonization rather than an indirect benefit through competitor release. The O₃ 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.