This was conducted to examine the potential responses of a tallgrass prairie in the US Great Plains to global warming under two land use scenarios. Infrared heaters were used to simulate climatic warming and clipping was used to mimic mowing for hay or grazing. Warming treatment significantly increased daily mean and minimum, but not maximum, air temperatures, resulting in a reduced diurnal air temperature range. Infrared heaters substantially increased daily maximum, mean, and minimum soil temperatures. Clipping increased daily maximum and mean soil temperatures, but decreased daily minimum soil temperature. Both warming and clipping reduced soil moisture.

Experimental warming in the tallgrass prairie significantly increased green aboveground biomass (AGB) in early spring and late autumn when temperatures were low, but had a negative direct effect on peak AGB in summer when temperatures were high. Warming increased net N mineralization in the first year but reduced it in the second year. Elevated temperature did not affect peak AGB in 2000, but significantly increased the peak AGB 13% and 27% without and with clipping in 2001.

Warming increased stems, percent cover, dry mass per ragweed stem, aboveground biomass (AGB), and the ratio of ragweed AGB to total AGB of an allergenic species, western ragweed (Ambrosia psilostachya DC.). Clipping increased ragweed stems by 75% and 36% in the control and warmed plots, respectively. Warming also increased total pollen production per unit area and pollen diameter. The results from our experiment suggest that global warming could aggravate allergic hazards and thereby jeopardize public health.