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Two long-term environmental manipulation experiments, using perspex screens to alter aspects of the thermal and radiation climate, have been installed over soil ecosystems at Mars and Ares Oases on southern Alexander Island (c. 72degreesS). These ecosystems are based on autotrophic microbes and meiofaunal groups. Initial results from the Mars Oasis manipulation (commenced in November 1997) identified rapid and large changes in soil nematode communities after only 1 year, with population increases of 2-3 orders of magnitude, although no consistent effects were apparent for tardigrade and rotifer populations. The same soils were resampled during November and December 2000, along with soils from the series of screens deployed at the neighbouring Ares Oasis in January 1995. At Mars Oasis increases in nematode population densities over bare ground controls were again apparent. However, these were much smaller than found in 1998/9 and densities were now comparable to those found in local naturally vegetated ground. Further, while the majority of the increase observed after 1 year was accounted for by the single microbivorous genus, Plectus, after 3 years community complexity had increased to include several omnivorous genera and diversity was also now comparable with local naturally-vegetated ground. Responses to the 5 year manipulation at Ares Oasis were similar in some regards to the first year results at Mars Oasis (also finding a considerable increase in population densities), but did not show the same pattern of increasing complexity seen subsequently at Mars.