Ten 3×10 m plots are located on an east to southeast facing glacial moraine, with their long dimension parallel to the hill slope. Control and experimental plots alternate and are separated by a 3 m gap to ensure that control plots are not affected by the warming experiment. Electric heaters are suspended 2.5 m above experimental plots from steel cables attached to steel towers at the corners of the plots. The electric heaters provide uniform heating (22 watts per square meter) to simulate warming predicted due to doubled atmospheric carbon dioxide levels. Heaters have been turned on, day and night, year-round since 1990.

Based on slope, vegetative cover, and soil properties, each plot is divided into upper (U), middle (M), and lower (L) zones. Zones U and M are relatively dry and sparsely vegetated; zone U is much less steep than zone M, which has an average slope of 15 degrees. Zone L is relatively flat and lush; its soils tend to be moist because surface water collects in this part of the landscape.

Next Step – Look at the Data.