PARENT SESSION
Oral Session # 96: Disturbance Ecology: Wind and Water.
Presiding: L Battaglia
Friday, August 8. 8:30 AM to 12:00 PM, SITCC Meeting Room 202.

Role of disturbance and seed density on seedbank formation and population dynamics in Helianthus annuus.

Moody-Weis, Jennifer ^*,1, Alexander, Helen ¹, ¹ University of Kansas, Lawrence, Kansas

ABSTRACT- The role of seedbanks in determining plant population abundance, structure, and dynamics is beginning to be realized. However, we know little about what factors influence seedbank formation. In annual, weedy species, it is clear that soil disturbance plays a major role in determining the fate of seeds in the soil. Helianthus annuus is a weedy species that is native to the Great Plains, is commonly found in disturbed habitat, and forms persistent seedbanks. The goal of this study is to determine how different disturbance regimes and seed densities influence the formation of seedbanks and, in turn the role of the seedbank in the population dynamics of H. annuus. Specifically I am addressing the following questions:1.) How does the timing of disturbance relative to seed dispersal influence the formation of a persistent seedbank? 2.) Does the density of seeds dispersed influence seed bank formation? 3.) Are populations limited by the presence of safe-sites (i.e. disturbance) or by the availability of seeds (i.e. seed density)? In 2001, I set up 210 experimental populations, representing 21 treatments of different combinations of seed density, pre-dispersal disturbance, and post-dispersal disturbance. Data were collected on the numbers of seedlings that emerged, the number of plants surviving to reproduction and the reproductive output per population. Soil samples from each population were collected and sieved to estimate the number of seeds remaining in the soil. In 2002, more seedlings germinated in plots that had a large disturbance compared to those with no disturbance or a small disturbance. Also, higher seed density lead to higher seedling emergence. In most cases, the differences in seedling density appear to carry over into number of flowering plants and the number of flowers produced. In fall of 2002, all plots were disturbed, which should create ideal germination conditions. Data will again be collected in 2003. Germination and seed sieving results from both 2002 and 2003 will allow me to evaluate the mechanisms that lead to variation in seedbank formation. This study is important as it experimentally examines the role of disturbance in seed bank dynamics.

Key words: soil distrubance, seed bank, Helianthus annuus , population biology