A simple empirical model of salt marsh plant spatial distributions with respect to a tidal channel network

Previous work has shown that the distribution of plant species in a salt marsh near Petaluma, CA, is strongly influenced by the location and size of tidal 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 order (a surrogate for channel cross-sectional area.) Plant species distributions predicted with this channel influence function compared favorably to known distributions in Petaluma Marsh. Using this function and probabilities estimated from transect vegetation data, we simulated the two-dimensional pattern of species abundance across the entire site. Comparisons of predictions with independently generated field maps showed comparable patterns of cover for most species. The results indicate that the distribution of vegetation in Petaluma Marsh, both major zones of marsh dominants and patches of minor species, can be described by a single, empirical factor: cumulative distance from tidal channels of different size.