ISLANDS OF LIFE AT 6000 M ALTITUDE - THE ENVIRONMENT OF THE HIGHEST AUTOTROPHIC COMMUNITIES ON EARTH (SOCOMPA VOLCANO, ANDES)

A November-December 1984 expedition to the Socompa Volcano in the Andes (24-degrees-25'S) rediscovered and described six complex autotrophic communities on geothermal warmspots near the summit at 5750 to 6060 m. These complex communities are unique in terms of their isolation, altitude, and biota, and are considered highly fragile. Environmental parameters were measured and standardized germination trials were used as bioassays of microclimate. Observations were performed on two successive ascents at a 7-d interval, with a total of 8 d recorded. The communities were composed mainly of mosses and liverworts, but included also algae, fungi, and lichens. In all, 36 taxa of bryophytes and lichens have been recognized in less than 400 m2 of vegetation. The communities formed dense patches of up to 200 m2 on warm soils (22 to 31-degrees-C at -10 cm depth) around steam vents and at cave entrances emitting vapor (9-37-degrees-C). Insects, a bird (Sicalis olivaceus), and a rodent (Phyllotis darwini rupestris) were also present. Air temperatures during the visit fluctuated between -12.1 and +9.0-degrees-C, with a daily mean of -5.5-degrees-C and a relative humidity mean of 78%. Diurnal temperature amplitude near the surface outside warmspots was up to 31-degrees-C at +2 cm and 56-degrees-C at 0 cm. The mean vapor pressure deficit at +60 cm was 1.1 mbar with an absolute maximum of 5.5 mbar. Pan-evaporation registered over 3.5 mm d-1, but soils were moist below the surface gravel and moist up to the surface at warmspots. This characterizes a cold environment with high surface temperature amplitudes and moderate to high moisture. Hundreds of kilometers separate these patches from any possible source of diaspores, at least for most of their components.