Predicted Effects

As a result of the attention paid to the effects of global warming on various groups of organisms and various ecosystems, some lichenologists have addressed the question of what effects global warming might have or have had on lichens.

Nash and Olafsen [4] predict that global warming in arctic areas may have a positive effect on lichens with cyanobacteria as photobiont, because the conditions for nitrogen fixation will improve. They reasoned that under field conditions of optimal water hydration, lichen photosynthesis is primarily light-limited and nitrogen fixation is temperature-limited in both Peltigera canina and Stereocaulon tomentosum at Anaktuvuk Pass, Alaska. Thus, they continued, 'where duration of optimal hydration conditions remains unchanged from the present-day climate, the anticipated temperature increases in the Arctic may enhance nitrogen fixation in these lichens more than carbon gain. Because nitrogen frequently limits productivity in Arctic ecosystems, the results are potentially important to the many Arctic and subarctic ecosystems in which such lichens are abundant'. The expected effect will be a spread of these species at the cost of other lichens and/or plants. So far, this has not been unequivocally observed; rather the contrary: lichens have recently decreased in arctic regions, probably due to the increase in phanerogams [5].

Insarov and Schroeter [6] and Insarov and Insarova [7] predict that lichens might, like other groups of organisms, show a response to global warming. As lichens are generally swift colonisers that disperse well, not only negative changes (extinctions) might be observed but also new invasions of more warmth-loving species in areas where they have not occurred before. In order to detect such changes, they installed some base-line monitoring transects across steep climatic gradients, but so far, no results have been reported.

Ellis and co-workers [3,8] predict the response, in terms of changed distribution on the British Isles, of groups of lichens with different current distribution patterns and known ecological preferences, based on the current distribution and on several different climate scenarios. Although numerous historic data are also available, no unequivocal correlation between global warming and past changes in the lichen flora of the British Isles has been shown.

Zotz and Baader [9] describe the different projected scenarios as regards lichens and bryophytes in the different biomes in the world.

Finally, as a result of widespread melting of glaciers, new habitats for (especially) stone-inhabiting lichen are being formed. However, only the pioneer species can be expected to benefit from this.

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