Passive open-top devices have been proposed as a method to experimentally increase temperature in high-latitude ecosystems. There is, however, little documentation on the efficacy of these devices. This paper examines the performance of four open-top chambers for altering temperature at six sites in the Arctic and Antarctica. Most of the heating effect was due to daytime warming above ambient; occasional night-time cooling below ambient, especially of air temperatures, depressed mean daily temperature. The mean daily temperatures at four arctic sites were generally increased by 1.2-1.8°C; but occasionally, temperature depressions also occurred. Under optimal conditions at the antarctic site (dry soils, no vegetation, high radiation) mean daily soil temperatures were increased by ⍣2.2°C (-10 cm) to ⍣5.2°C (0 cm). Protection from wind may play a more important role than temperature per se in providing a favourable environment for plant growth within opentop devices. Wind speed had a generally negative impact on mean daily temperature. Daily global radiation was both positively and negatively related to chamber temperature response. The effect of chambers on snow accumulation was variable with the Alexandra Fjord site showing an increased accumulation in chambers but no difference in the date of snowmelt, while at Latnjajaure in a deep snowfall site, snowmelt occurred 1-2 weeks earlier in chambers, potentially increasing the growing season. Selection of a passive temperature-enhancing system requires balancing the temperature enhancement desired against potential unwanted ecological effects such as chamber overheating and altered light, moisture, and wind. In general, the more closed the temperature-enhancing system, the higher is the temperature enhancement, but the larger are the unwanted ecological effects. Open-top chambers alter temperature significantly and minimize most unwanted ecological effects; as a consequence, these chambers are a useful tool for studying the response of high-latitude ecosystems to warming.

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Three plant communities studied at a high arctic oasis on Ellesmere Island responded to nutrient addition. Response to nitrogen was greatest in the driest community and weaker in the more mesic and wet-mesic communities. Nutrient addition resulted in (i) increased inflorescence densities of dicotyledonous and certain graminoid species; (ii) increased tiller densities of wet sedge species; and (iii) increased net production of graminoids and forbs at high rates of application, and in some dwarf shrubs at lower rates. These results parallel those of studies at lower latitudes in the Arctic, and support the hypothesis that arctic ecosystems are typically oligotrophic.

Cyanobacteria and eukaryotic algae were investigated during three seasons in 18 plots established across Sverdrup Pass valley of central Ellesmere Island, 79°N, Canada. The sites differed in altitude, substratum, and other characteristics. A high species diversity totalled 136 taxa. Cyanobacteria accounted for 52 and eukaryotic algae 84 species. In both groups, numerous species did not correspond to any taxa described. However, high diversity did not always coincide with high algal abundance or biomass. On older and stable landscapes, visible crusts developed, containing mostly cyanobacteria, fungi, and other microbial components. Considerable variation in algal diversity and abundance was found among the sites. Also the southern, granitic portion of the pass was richer in green algae compared to its northern, dolomitic portion where motile cyanobacteria were more prominent. These micro-autotrophs occupied the soil profile to a depth of 7 cm. Their highest density was not at the surface but at 3–4 cm depth. One plot was contaminated by windblown copper-rich dust from a nearby outcrop and soil here was poorest in content of photosynthetic pigments, suggesting a local heavy-metal toxicity.