PARENT SESSION
Poster Session # 11: Disturbance Ecology.

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

The immediate effect of fire on the soil seed bank of pinyon-juniper woodlands.

Allen, Elizabeth^*,1, Nowak, Robert¹, ¹ University of Nevada-Reno, Reno, Nevada

ABSTRACT- Fire is a common agent of disturbance that can vegetatively denude an area. Once a site is denuded, the soil seed bank is a major source for new plant recruitment and therefore important to understand. I am studying the immediate effect of fire on the seed bank in the P-J woodlands of central Nevada. My study site is comprised of three medium density P-J plots that contain three microsites: under-tree, under-shrub and interspace. On May 11, 2002 a prescribed burn was applied to the plots. I obtained pre-burn soil samples a week before the fire and post-burn soil samples one week after the fire. Because different microsites have differing abilities to trap seeds, I obtained 10 samples from each of the three microsites. I also took the soil samples at different depths: litter (under-tree only), 0-1cm, 1-5 cm and 5-10 cm. These soil samples were placed in flats in a greenhouse and induced to germinate. Surprisingly, the data have shown that the number of seedlings emerging from the post-burn samples increased by 67%. I had hypothesized that there would be a loss of viable seeds in the soil for two reasons. First, heat from the fire would have deleterious effects on the seed bank. Second, in May there would be no new influx of seeds to the soil, and the number of viable seeds in the seed bank should have decreased between the pre- and post-burn samples due to natural germination at the site. The under-tree microsite is driving the increase, especially the 0-1 cm layer where the number of seedlings increased 4.5 times. The two most common species within this microsite and at this depth are the native annual mustard Descurainia pinnata and quaking aspen, Populus tremuloides. Various mechanisms to account for the increase in seed germination are discussed.

Key words: Pinyon-Juniper Woodland, soil seed bank, Fire