EFFECTS OF EXPERIMENTAL TEMPERATURE ELEVATION ON HIGH-ARCTIC SOIL MICROARTHROPOD POPULATIONS

An experiment was conducted to measure the effects of summer warming o n the total population densities of soil-dwelling microarthropods in t he high Arctic and to compare these results with those from natural be tween-year and between-site variations. Small polythene tents were use d to elevate summer temperatures over 3 years on polar semi-desert and tundra heath in West Spitsbergen, Svalbard, Norway. Soil cores were t aken at regular intervals from tented and untented (control) plots and heat extracted for mites (Acarina: Oribatida) and springtails (Collem bola). Species present were similar at both sites, but at the start of the experiment total springtail populations were greater at the polar semi-desert whilst oribatid mite densities were equal at both sites. No significant effect of temperature elevation on oribatid mite popula tions emerged, even after 3 years. By contrast, springtail numbers wer e significantly lower on tented versus control plots at the polar semi -desert at the end of year 3, but not so at the tundra heath. Collembo la numbers declined at both sites during the warm dry mid-summers of 1 992/1993 and this was most marked at the better drained polar semi-des ert site. Over the equivalent period total oribatid mite populations, while relatively more stable, increased significantly at the polar sem i-desert as a result of an increase in the number of juveniles. Result s are interpreted in the context of the ecophysiological adaptations o f oribatid mites and springtails to soil temperature and moisture. The resulting survival characteristics are considered in relation to the temperature and moisture characteristics of the two sites. The experim ent demonstrated that year to year variation in climate, interacting w ith physical differences between sites, produced an equal or greater e ffect on microarthropod numbers at any one site than the 8-10% increas e in ''heat availability'' (day degrees above zero) resulting from the summer tent treatment. The limitations of the use of tents to elevate soil temperatures are discussed. Comparisons are made with microarthr opod population data from other polar and alpine sites.