Uncertain Effects

Some observed and reported changes in the lichen flora cannot be unequivocally attributed to global warming. There are several reasons for this but the most common one is that comparable historic or background data are wanting. Also climate change is not the only change taking place and some of the changes occurring locally may interact or even counteract. Examples are isolated finds of warmth-loving species in more boreal countries, like Flavoparmelia caperata in Denmark, reported by S0chting [13] and attributed by him to global warming.

Another type of uncertainty is the intermittent and sometimes devastating effects of El Nino on coastal lichens along the Pacific coast of South America and on the Galapagos Islands. These have been documented, for example, by Follmann [14] and attributed directly to El Nino. The question remains

FIGURE 1 The distribution of lichen species with Trentepohlia phycobiont in the Netherlands province of Zeeland, in 1997, 2000, 2003 and 2006. The dot size refers to the number of species per site [12].

□ cold %

□ cool %

□ average %

□ rather warm %

□ warm %

□ very warm %

FIGURE 2 Changes of the epiphytic lichen composition in the Netherlands province of Zeeland in relation to temperature preference. The percentages are derived from species' frequencies per year. The total number of species for which a temperature preference is known is given as 100% [12].

FIGURE 2 Changes of the epiphytic lichen composition in the Netherlands province of Zeeland in relation to temperature preference. The percentages are derived from species' frequencies per year. The total number of species for which a temperature preference is known is given as 100% [12].

whether the intensity of the El Nino effects is changing due to global warming, or not. In any event, lichens appear to have suffered more during the past few decades than ever before.

In some cases the patterns and processes are confused. An example is the reported work by Cezanne and co-workers [15] claiming that changes in lichen were indicators of climate change. However, all the observations were made within a year and the various stations were visited only once; the paper describes the correlation of the lichen vegetation with climatic parameters, but only a spatial pattern is shown. In summary the conclusion made, does not bear up to scientific scrutiny.

0 0

Post a comment