CHANGES IN GEOTHERMAL VEGETATION AT MYVATN, ICELAND, AND COMPARISONS TO OTHER GEOTHERMAL AREAS

Absztrakt

We sampled 207 plots from 15 transects at the Myvatn geothermal area in Iceland in 1985, one year after the September 1984 eruption of Krafla, and again in 1987, and compared the species and community structure to that of other sites we had visited in Japan and New Zealand. We found 5 lichen, 47 bryophyte, and 28 tracheophyte species at Myvatn. Overall Shannon diversity (H’) was high at 4.34, with Brillouin (information-theory-based) species diversity (H’) being very similar at 4.32. The greatest diversity occurred at > 25–35°C surface temperature and the least at > 60°C. Zones are defined mostly by temperature and humidity, with Cyanobacteria closest to the vents in the hottest zones, followed by bryophytes, then lichens, then tracheophytes. Bryum argenteum, Ceratodon purpureus, and Fossombronia sp. 1 (probably immature F. foveolata) occupied the highest temperatures near the vents in 1985. Lichens tended to avoid hot soils with high humidity. Soil chemistry most likely plays a role, but with so many variables and many values at unquantifiable levels, we considered it premature to determine their individual effects. By 1987, Bryum argenteum, a near-vent species, had almost totally disappeared, along with the steam emissions where they had thrived. The geothermal areas in cold climates could serve as refugia for more temperate species that may have existed prior to the Ice Age, or they may simply be suitable habitats for northern extensions of the species. This study gives us a glimpse of potential vegetational changes resulting from climate changes as demonstrated in three regions of the world.