PARENT SESSION
Poster Session # 7: Restoration, Resource Management, and Conservation.

Monday, August 4 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.

Heat tolerance of grass seeds in desert grasslands and their vulnerability to prescribed burning.

Ortiz-Barney, Elena^*,1, Stromberg, Juliet¹, ¹ Arizona State University, Tempe, AZ

ABSTRACT- Over the last 100 years, large areas of desert grassland in the US Southwest have shifted to shrublands. Land managers are experimenting with the use of prescribed burning to restore these areas to grasslands. A previous study of ours indicated that there is potential for regeneration of the herbaceous community from the soil seed bank. However, within the soil seed bank, the majority of seeds were found in the litter layer rather than the soil. Due to their location, the available seeds will likely be exposed to lethal temperatures during a fire. In this study, we measured maximum fire temperatures during prescribed burns at two field sites and at two depths (soil surface and 2-3 cm below surface). During prescribed burning, maximum fire temperatures were extremely variable. However, the maximum temperature on the surface of the soil was higher than below the surface. Most temperature values recorded on the soil surface ranged between 50° and 350°C whereas, sub-surface most temperature values were between 50° and 100°C. We also tested the heat tolerance of seven southwestern range grasses by placing dry seed in an oven for 2 minutes at a range of temperatures (50° to 300°C). Of the grass seeds that germinated under laboratory conditions, none germinated after being exposed to temperatures above 100°C. These results indicate that prescribed burning may damage viable seed reserves on the surface of the soil, although the patchy nature of the burns may allow for local survivorship.

Key words: seeds, heat tolerance, desert grassland, prescribed burning