Abiotic limitation of non-native plants in the high salt marsh transition zone.
Native plants in the upland to high-marsh transition zone of southern California salt marshes are mostly perennials and therefore experience the abiotic stress of low soil moisture and high soil salinity throughout much of the year. However, many annual non-native plants reproduce during the brief period of reduced salinity and increased moisture during winter rainfall. We investigated the seasonal and spatial variation in vegetation and soil properties of the transition zone using an observational study. Next, we explored the potential for managing non-native plants using a field experiment with varying timing, quantity, and frequency of salt addition treatments. The observational study showed that the distribution of non-native plants is related to changes in soil salinity and soil moisture that accompany changes in elevation, although there are variations among species. In the field experiment, salt was effective at reducing non-native plant cover, but the timing of treatment was important. Although additional work is needed to refine the salt treatments, this work supports the idea that altering abiotic conditions can effectively reduce the presence of non-native species in the upland to high-marsh transition zone.