ABSTRACT. Management actions to protect endangered species and conserve ecosystem function may not always be in precise alignment. Efforts to recover the California Ridgway's Rail (Rallus obsoletus obsoletus; hereafter, California rail), a federally and statelisted species, and restoration of tidal marsh ecosystems in the San Francisco Bay estuary provide a prime example of habitat restoration that has conflicted with species conservation. On the brink of extinction from habitat loss and degradation, and non-native predators in the 1990s, California rail populations responded positively to introduction of a non-native plant, Atlantic cordgrass (Spartina alterniflora). California rail populations were in substantial decline when the non-native Spartina was initially introduced as part of efforts to recover tidal marshes. Subsequent hybridization with the native Pacific cordgrass (Spartina foliosa) boosted California rail populations by providing greater cover and increased habitat area. The hybrid cordgrass (S. alterniflora × S. foliosa) readily invaded tidal mudflats and channels, and both crowded out native tidal marsh plants and increased sediment accretion in the marsh plain. This resulted in modification of tidal marsh geomorphology, hydrology, productivity, and species composition. Our results show that denser California rail populations occur in invasive Spartina than in native Spartina in San Francisco Bay. Herbicide treatment between 2005 and 2012 removed invasive Spartina from open intertidal mud and preserved foraging habitat for shorebirds. However, removal of invasive Spartina caused substantial decreases in California rail populations. Unknown facets of California rail ecology, undesirable interim stages of tidal marsh restoration, and competing management objectives among stakeholders resulted in management planning for endangered species or ecosystem restoration that favored one goal over the other. We have examined this perceived conflict and propose strategies for moderating harmful effects of restoration while meeting the needs of both endangered species and the imperiled native marsh ecosystem.
Urbanization and anthropogenic development have fundamentally altered ecosystem dynamics on a global scale. Conservation and management of comparatively less modified landscapes adjacent to highly modified landscapes requires careful consideration of interactions between landscape types. Restoration or conservation of habitat within a developed matrix is generally thought to have beneficial effects on landscape-level ecological processes. We propose an ecological spillover framework to critically assess how restoring or conserving species populations within anthropogenically modified landscapes may affect adjacent wildland populations. Within the framework, the spillover process is divided into seven interconnected 'nodes', which identify points at which potential cause-effect relationships may exist between urban and wildland populations. The framework is useful for a wide range of project-specific ecological relationships, and can help scientists and managers identify knowledge gaps and weigh risk in conservation decision-making. We queried the conservation literature to identify research focused on the impacts of urban species populations on regional wildland populations. Our search revealed seven ecological processes that have the potential to be affected by urban to wildland spillover and we found relatively few studies that explicitly analyze spillover effects from urban to wildland areas. Organisms living in urban areas within restored or remnant habitats located in an urban matrix, or within the built environment have largely unknown effects on landscape-level ecological processes. We conclude with a discussion on the critical gaps in research linking these habitats to larger landscape-level ecological understanding, and provide recommendations for research priorities that might illuminate this important aspect of 21st century conservation planning.
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