PARENT SESSION
Oral Session # 77: Plant Ecology VI: Temperature and Water Stress.
Presiding: C Ford
Thursday, August 7. 1:30 PM to 5:00 PM, SITCC Meeting Room 102.
Phenological differences among winter annuals in warmed plots in tallgrass prairie.
Sherry, Rebecca*,1, Wallace, Linda1, Luo, Yiqi1, Zehrbach, Nancy1, 1 University of Oklahoma, Norman, OK
ABSTRACT- The phenology of winter annuals in warmed and unwarmed plots in tallgrass prairie in central Oklahoma were followed for a 9-month period (October to July). Twenty 1.22m by 2.44m plots with a surrounding 0.3m buffer were observed monthly from October 2002 to February 2003, and weekly beginning in March 2003. Half of the plots had two 1500 watt Kalgo infrared heaters hanging in the center of the plots 1.4m above the ground. The remaining ten plots have dummy heaters in the same position. The first two centimeters of soil in heated plots was 4 oC warmer than soil in unheated plots during February 2003. Heating began in mid-February 2003. Japanese brome, Bromus japonicus, germinated by the beginning of October 2002 and is the dominate winter annual in all plots. Two suites of annual forbs were followed. The first set of forbs included small bluets (Hedyotis crassifloria), ridgeseed spurge (Euphorbia glyptosperma), and henbit (Lamium sp.). Hedyotis germinated in early November, while Euphorbia and Lamium germinated in late November. Hedyotis was the first plant to bloom at the site, in late February. A second suite of species, dominated by Rumex sp., germinated in January and consisted primarily of rosette forming annuals. These rosette-forming annuals were much less numerous than the first suite of forbs. Clipping of the plots for biomass measurements in the fall of 2002 may have been deleterious to perennial, non-rosette forming forbs but may have benefited winter annuals by eliminating the canopy of standing dead tallgrass. The relative influence of day-length and temperature on the phenology of winter annuals will be discussed.
Key words: Oklahoma, interannual climate variation, tallgrass prairie, phenology