Background/Question/Methods Until recently, experimental studies of climate change focused on temperature or precipitation, but rarely both. Additionally, warming studies almost universally focused on the effects of a single step increase in temperature. It is not known whether most ecosystem and community variables respond unimodally, linearly or otherwise to temperature increases, or how these responses would be affected by accompanying changes in precipitation. The Boston-Area Climate Experiment (BACE) was constructed to address these issues. The BACE imposes a factorial combination of precipitation and temperature manipulations on old-field plots. Unlike most previous experiments, the BACE features four levels of warming, enabling tests of the hypotheses that species- and ecosystem-level responses to warming are nonlinear, and that the character of these responses depends strongly on precipitation. The experiment uses infrared heaters to achieve warming, with feedback control from infrared radiometers. Rainout shelters remove half of the incoming precipitation from the drought treatment and this water is immediately sprinkled on the wet treatment. Here, we report the environmental changes achieved to date by the experimental manipulations in the BACE.

Results/Conclusions Precipitation and warming treatments both affected soil moisture, with markedly drier soils in drought plots and less dramatic soil drying in warmer plots. While canopy warming consistently reached targets at night, warming achieved in the daytime varied with environmental conditions. During the growing season, soil temperatures were consistently warmer in the warmed plots, and warming penetrated to at least 10 cm depth. In the winter, heaters melted snow off the warmest plots, leading to intervals in which the warmed plots had cooler soils than the unwarmed plots, presumably because the snow insulated the soil. These islands of uncovered ground also appeared to preferentially attract some herbivores. We discuss the benefits and drawbacks of the technologies used at the BACE, and the potential consequences of the observed treatment effects for the “realism” of biogeochemical and plant community measurements.