OPEN-TOP DESIGNS FOR MANIPULATING FIELD TEMPERATURE IN HIGH-LATITUDE ECOSYSTEMS

Passive open-top devices have been proposed as a method to experimenta lly increase temperature in high-latitude ecosystems. There is, howeve r, little documentation on the efficacy of these devices. This paper e xamines the performance of four open-top chambers for altering tempera ture at six sites in the Arctic and Antarctica. Most of the heating ef fect was due to daytime warming above ambient; occasional night-time c ooling below ambient, especially of air temperatures, depressed mean d aily temperature. The mean daily temperatures at four arctic sites wer e generally increased by 1.2-1.8 degrees C; but occasionally, temperat ure depressions also occurred. Under optimal conditions at the antarct ic site (dry soils, no vegetation, high radiation) mean daily soil tem peratures were increased by +2.2 degrees C (-10 cm) to +5.2 degrees C (0 cm). Protection from wind may Flay a more important role than tempe rature per se in providing a favourable environment for plant growth w ithin open-top 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 cha mbers 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, snowm elt occurred 1-2 weeks earlier in chambers, potentially increasing the growing season. Selection of a passive temperature-enhancing system r equires balancing the temperature enhancement desired against potentia l 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 te mperature significantly and minimize most unwanted ecological effects; as a consequence, these chambers are a useful tool for studying the r esponse of high-latitude ecosystems to warming.