Document: TRA-3-36-11

Seed banks of Iliamna longisepala (Malvaceae), a rare, fire dependent plant from Washington State.

FUENTES, T.L.* and J.C.STROMBERG

Arizona State University, Tempe, AZ, U.S.A. ¹

Abstract:
A rare herbaceous perennial, Iliamna longisepala (Torr.) Wiggins is endemic to north-central Washington state. During the 1980's, most populations were small and consisted of reproductively mature individuals. Seedling recruitment after large fires in 1988 and 1994 suggests that fire scarification stimulates germination of seeds in persistent soil seed banks. We assessed the size and distribution of these seed banks at 12 sites, four from each of three fire histories (unburned since 1960, burned in 1988/89, or burned in 1994). We collected 105 soil cores (2.54cm x 10cm deep) per site. Total soil surface area sampled was 532 cm²/site. After dry sieving, samples were examined under a dissecting scope, and all I. longisepala seeds were removed. Seed densities ranged from 0-959 seeds/m², with most seeds (81%) concentrated in the top 5cm of soil. Neither I. longisepala plant density nor fire history significantly affected seed density (Kruskal-Wallis test, p>0.10). However, the seeds appeared to clump around existing plants; seed density was significantly higher within 1m of established plants (Mann-Whitney U test, p<0.001). Seed density was also higher down slope from plants, but not significantly higher (Mann-Whitney, p>0.05). The patchy spatial pattern of I. longisepala plants at each site seemed to strongly influence the patchy distribution of seeds in the soil. To maximize seedling recruitment, prescribed fire plans should focus on areas containing existing plants and areas down slope from them.

Keywords: seed bank, Iliamna, fire, scarification

This abstract is being presented at: 3:30 PM in session:
REPRODUCTIVE ECOLOGY