Phytogeography and Ecology of Epiphytic Lichens at the Southern Rim of the Clay Belt (N-Ontario, Canada)

Abstract

releves of epiphytic lichen vegetation from the Elk Lake area (N-Ontario, Can- ada) were submitted to classtfication and ordination. Eight community types were recognized. The main ecological factors underlying the compositional variation of the releves is pH. Each com- munity type is characterized by species with different distribution patterns in North America. Dif- ferences in the phytogeographical affinities of the community types are related to differences in ecological conditions. A comparison with data from an analogous study performed by the author in the Carnic Alps (Italy), shows that there is a high degree offloristic and structural convergence between communities of the two sites. Several species are common to the lichen floras of Europe and North America. According to Ahti (1964), 85% of the macrolichens of Northern On- tario also occur in Europe, and the floristic simi- larity between the two continents increases from South to North. A comparison between epigaeic lichen synusiae from the Yukon Territory and from Europe (Nimis 1981) revealed strong floristic sim- ilarities between communities occurring under sim- ilar ecological conditions. A thorough discussion of the lichen flora and vegetation in the boreal zone is provided by Ahti (1977). As far as epiphytic lichen vegetation is concerned, according to Ahti (1977) the overall picture is quite fragmentary and the gen- eral phytogeographical features are not precisely known at all.