Print PageClimate in dryland ecosystems throughout the southwestern United States is rapidly changing and the Fourth Intergovernmental Panel on Climate Change report projects that temperatures within the Colorado Plateau could rise by 4–6oC by 2100, with an overall decrease in precipitation and a shift to pulsing summer rainfall. The goal of this study was to assess the consequences of projected climate change for plant communities in these dryland ecosystems.
In a large field experiment near Moab, Utah, we manipulated temperature and precipitation to examine the combined effects of pulsing summer precipitation and warming on two native grasses, a native shrub, and the invasive annual grass Bromus tectorum (cheatgrass). The fully factorial field experiment consisted of five replicate 5m2 plots, located on shallow sand/silt soils, and randomly assigned in the following treatments: (1) increased warming, with two levels + 2°C and + 4°C, (2) increased warming (+ 2°C and + 4°C) and summer pulsing precipitation, (3) summer pulsing precipitation, and (4) control. An additional set of plots were established at a nearby site with coarser sandy soils and five replicates of 5m2 plots were randomly assigned in the following treatments: (1) increased warming + 2°C and (2) control. We measured plant phenological development, physiological performance, cover, and allometrically estimated biomass and reproductive output.
Results/Conclusions
Preliminary results indicate that phenology shifted in response to warming, with plants in warmed plots greening up earlier and reaching phenological phases more rapidly than plants in control plots. Accelerated phenology in cheatgrass were associated with increased cheatgrass cover, higher biomass, and increased seed production and these increases were progressively larger in +4°C plots than in +2°C plots. A follow-up greenhouse study revealed that cheatgrass seeds from warmed plots had higher germination rates than seeds from control plots. We observed no changes in the cover of native plants, but saw differences in the biomass of native grasses between warmed and control plots. We also observed signs of increased photosynthetic efficiency, as measured by dark-adapted quantum yield, for plants in warmed plots early in the growing season. While the data here represent two years of an on-going experiment, these results suggest that changes to climate projected for the Colorado Plateau will likely affect plant phenology, physiological performance, and especially the performance of the invasive annual Bromus tectorum.
