PARENT SESSION
Oral Session # 52: Fire Ecology III: Grasslands; Scrub.
Presiding: J Grace
Wednesday, August 6. 1:30 PM to 5:00 PM, SITCC Meeting Room 102.
Above and belowground fire-related temperatures in a cheatgrass (Bromus tectorum L.) infested Sierra Nevada yellow pine forest: Effects on cheatgrass seeds and native plants.
McGinnis, Thomas*,1, Keeley, Jon1, Brooks, Matthew2, Sanford, Robert3, Belnap, Jayne4, 1 U.S. Geological Survey-Biological Resources Discipline, Three Rivers, CA2 U.S. Geological Survey-Biological Resources Discipline, Henderson, NV3 University of Denver, Denver, CO4 U.S. Geological Survey-Biological Resources Discipline, Moab, UT
ABSTRACT- The unforeseen influx of cheatgrass following prescription burning in the old growth yellow pine forest of Kings Canyon National Park, California, emphasizes the need for more research on fire ecology. In 420 5x5 m treatment plots we have measured how fire may alter cheatgrass and native plant populations. This paper focuses on the range of temperatures that occur above and belowground in plots with different fuel loads and burning seasons, and how these relate to plant survival and recruitment. Late fall burns in 2001, with light fuel loads and high relative humidity, did not cause noticeable mortality in established perennial natives or in cheatgrass seeds. Soil temperatures at 5 cm belowground in the late fall burn reached a mean peak temperature of only 18°C, rising 5°C due to fire (+5°C). To simulate a longer fire return interval, additional fine fuels (5 cm-deep pine needles) were added in summer and fall 2002 burn-plots resulting in significantly higher above and belowground heating. At 2 cm belowground, needle-addition plots reached a mean peak temperature of 242°C (+98°C) in the summer and 155°C (+138°C) in the fall, while untreated plots reached 75°C (+40°C) and 69°C (+46°C), respectively. Emulating conditions in the field, we subjected cheatgrass seeds to several heat, cold and moisture treatments, then incubated them to determine mortality. Some dry seeds survived brief 120°C heating while wet seeds survived 100°C. From our lab results we predict that most, but not all of the seeds in needle-addition field plots should have been destroyed, while a significant number of seeds would have survived in the unaltered plots. Preliminary field observations in February 2003 agree with the predictions. We will discuss our final results from the spring 2003 growing-season.
Key words: cheatgrass, germination, Bromus tectorum , fire