Climate manipulation
Three climate treatments have been applied to 3x3m plots:
1. Temperature has been elevated from November to April each year, beginning in November 1993. Each heated plot contains two 1000 W, 240-V AC heating cables secured to the soil surface in parallel runs spaced 50mmapart. Soil surface temperature of heated plots is maintained at 3°C above ambient by thermocouples in heated and control plots linked to a PC-based control system.
2. Rainfall has been intercepted above the vegetation throughout July and August since the summer of 1994 by means of automatically operating, semitransparent shelters that slide across the plots at the onset of rain and retreat to an off-plot position when rain ceases. Plots of intercepted summer rainfall have significantly reduced summer soil moisture levels compared with control plots, particularly within the interior 2 x 2 m subject to vegetation monitoring. In 2004, a decision was made to shift the drought treatment to alternate years (thus suspending simulated droughts in 2004 and 2006).
3. Since 1994, additional water has been added on a monthly basis to the plots during the months of June to September (inclusive), to maintain an input at least 20% above the long-term (1972–1982) Buxton average for each month.
In addition to treatments 1, 2, and 3, two combinations, (1&2) and (1&3),have been maintained. All five treatments, together with untreated controls, are included in a fully randomized block, replicated 5 times.
