PARENT SESSION
Contributed Oral Session 29: Climate Dynamics: Arid Land Responses to Variability in Rainfall
Monday, August 8, 1:30 PM - 5:00 PM, Meeting Room 520 A, Level 5, Palais des congrès de Montréal

Three year's data on the effects of interannual variation in temperature and precipitation on grassland production and community structure.

Sherry, Rebecca^*,1, Luo, Yiqi¹, Wallace, Linda, Arnone, Jay², Verburg, Paul², Johnson, Dale², Schimel, D, ¹ University of Oklahoma, Norman, OK² Desert Research Institute, Reno, NV

ABSTRACT- A three-year study in tallgrass prairie was designed to ascertain whether or not the variation in temperature and precipitation in one year can have ecosystem feedback effects in subsequent years. Twenty tall-grass prairie plots were monitored during a pre-treatment year, a treatment year, and a post-treatment year. During the treatment year, temperature was raised 4°C in ten heated plots and natural precipitation was doubled in five of the heated and five of the unheated plots. Production and community structure were measured three times a year in April, at the end of August or the beginning of September (at peak biomass), and late November or early December. The treatment year coincided with a drought. During the treatment year total biomass declined compared to the previous year and rebounded the following year. Heat and extra-water effects on growth significantly increased total biomass in April of the treatment year; a similar, but non-significant, pattern was found for peak biomass. In late November/early December, a soil water deficit had developed in the heated plots; they had less biomass and a greater proportion of C4 plant biomass than unheated plots. In the post-treatment year, previously heated plots had significantly less biomass in April and also tended to have less biomass at peak biomass, but there were no post-treatment effects of the treatments on total biomass in the late November/early December. Relative cover of graminoids, particularly C4 species, increased during the treatment year. During April, heated plots had proportionally greater cover of C4 graminoids and less C3 graminoid cover than unheated plots. No differences between treatments in community structure were detected at peak biomass. In late November/early December, heated plots had greater cover of C4 species while C3 species had more cover in unheated plots. In the post-treatment year, no differences in community structure remained between the treatments but the cover of C4 plants during late summer continued to rise, possibly a carry-over effect from the previous dry year. In sum, variation in temperature and precipitation in one year can affect biomass and community structure the following year, through delayed soil moisture recharge following high temperatures and drought.

Key words: Interannual variation, temperature, precipitation, primary production