Author to contact: E.W. Sanderson

Institution: University of California, Davis

Mailing Address: Department of Land, Air and Water Resources, University of California, Davis, Davis, CA 95616

Phone number: 916-752-5092

FAX number: 916-752-5262

E-mail Address: ewsanderson@ucdavis.edu

Presenter: E.W. Sanderson

Preference: Oral

1st Choice: 35 (wetland ecology), 2nd Choice: 12 (vegetation analysis)

SANDERSON, ERIC W.*, THEODORE C. FOIN, SUSAN L. USTIN. and STEVEN D. CULBERSON. University of California, Davis, Davis, CA 95616. Tidal channel influence describes the zonation and distribution of plant species in Petaluma Marsh, CA.

We hypothesized that the distribution of plant species in a salt marsh near Petaluma, CA, is strongly influenced by the location and size of tidal channels. Channel networks at interior and marginal sites were mapped using global positioning and geographic information systems. Plant species abundances were measured with distance from channels. Cluster analysis of the vegetation data revealed eight clusters of plant species which were consistent at each site. These clusters varied in frequency with distance from channel and with channel order and origin (i.e. natural or constructed "mosquito ditch" channels). We developed a simple mathematical model to measure the "channel influence" at each point as a cumulative function based on inverse squared distance to channel, length of potentially influential channel, and channel size. Using this function and probabilities estimated from the vegetation data, we simulated species abundances at the two sites. Comparisons of predictions with validation data sets were made to evaluate the accuracy of the model. The results show that vegetation distributions in the salt marsh, both major zones of marsh dominants and patches of minor species, can be described by a single factor: cumulative distance from tidal channels of different size.