Research Summary

Effects of human trampling and cattle grazing on salt marsh assemblages in Elkhorn Slough, California

The effects of human trampling on Salicornia virginica assemblages in Elkhorn Slough, California were experimentally tested at two sites using 9 levels of trampling intensity and frequency over 6 months, then allowing plots to recover for 1 year. Responses to cattle grazing also were examined. Human trampling at all levels decreased S. virginica height and flower production. Percent cover of S. virginica remained high (~90%) in intermediate and lightly trampled plots, but bare ground dominated in heavily trampled areas. Once trampling ceased, open space was first colonized by non-native upland plants or algae, and later, S. virginica. After 1 year of recovery, trampled S. virginica in heavily trampled areas was shorter than untrampled controls, bare patches remained in some plots, and there were significant differences between invertebrates present in heavily trampled areas and controls.

Actively grazed cattle pasture was characterized by high percentages of bare ground and Distichlis, while ungrazed marsh was comprised of over 90% S. virginica. However, plants grazed by low densities of cattle responded quickly to the removal of livestock. After 15 months of recovery, Distichlis and bare ground declined, and S. virginica increased.

Overall, trampling and grazing can decrease S. virginica abundance, lead to changes in community structure, promote invasions by introduced species, and contribute to loss of marsh habitat.