Document: CHA-3-65-38

The effects of dispersal and competition on the population dynamics of two dominant California coastal sage scrub species; California buckwheat and White sage.

CHALEKIAN, J.S.* and D.H.DEUTSCHMAN

San Diego State University, San Diego, CA 92182 ¹

Abstract:
Southern California is one of the most floristically diverse regions in the world. However, recent data suggests native plant populations are being reduced by both habitat destruction and the competitive effects of invasive annuals. Our study focused on 1) modeling the dispersal kernels of two dominant California coastal sage scrub species (California buckwheat and White sage), and 2) determining what factors most affect their probabilities of establishment. Dispersal kernels were quantified using a seed trap experiment and modeled using non-linear regression. Seed traps were anchored into the ground, beginning at the canopy perimeter of a fruiting adult. Traps extended to a distance of 3 meters, at 1-meter intervals in all cardinal direction. The number of seeds was found to decay exponentially with distance, but decay rates differed dramatically between the two species. At a distance of 2 meters from the source, the number of buckwheat seeds decayed by a mean of 96%, where the number of sage seeds only decayed by a mean of 60%. To understand factors that most affect establishment, sites containing established juveniles were located and compared to adjacent non-established sites for fine scale variation in local surroundings. Variables measured were percent cover weeds, seed density, gopher disturbance, and soil penetrability. Logistic regression models indicated both proportion of weeds and seed density significantly affected the probability of establishment of buckwheat. However, the probability of establishment for sage was only affected by proportion of weeds. The combined results suggest both species are negatively affected by the presence of invasive annuals; however due to the difference in dispersal kernels, species specific population dynamics may vary dramatically at the local scale. These local scale dynamics may provide useful information for future management decisions.

Keywords: Coastal Sage Scrub, California Buckwheat, White sage, Dispersal kernel, Establishment, Non-linear regression, Logistic regression, Competiton

This abstract is being presented at: 3:30 PM in session:
Oral Session #68: Dispersal of Seeds and Fruits.