Adaptive management of perennial pepperweed for endangered specias and tidal marsh recovery

Authors: Grewell, Brenda; Futrell, Caryn; FORBERT, MICHAEL - West Coast Wildlands; Skaer Thomason, Meghan

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 2/17/2016
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Perennial pepperweed has invaded a wide range of habitat types in the far west. In the San Francisco Estuary, dense infestations have impacted sensitive tidal wetlands and compromised endangered species recovery efforts. An adaptive management effort to reduce perennial pepperweed was initiated by California State Parks at Southampton Bay Wetland Natural Preserve, Benicia. We evaluated management at two spatial scales using large-scale GIS-based assessments of target weed and endangered plant populations, in addition to a habitat-scale field experiment. Our objectives were to 1) assess the marsh-wide distribution and abundance of perennial pepperweed and endangered plant populations by microhabitat types to establish conservation zones and treatment approaches, and 2) evaluate efficacy of foliar-applied glyphosate treatments to perennial pepperweed in three tidal inundation zones and two microhabitat types for four years. Results were used to inform annual management decisions, and to maximize success of weed control while avoiding non-target impacts to endangered plants and ground-nesting marsh birds. In the experiment, weed response measures included live above ground biomass, stem density, % cover, and total non-structural carbohydrate concentration of below ground storage organs. All measured responses were significantly reduced by glyphosate treatments, though the magnitude of treatment effectiveness varied by year and microenvironment. Variation in treatment effectiveness was greatest in mid-marsh inundation zones near slough edges, prompting greater applicator attention to these areas. Marsh-wide, ground-based GPS mapping documented an 84% decrease in perennial pepperweed, with extant stands reduced to trace cover levels and only minor untreated areas remaining at higher cover. During the project, the total occupied area of the endangered plant population increased by over 200%. These results demonstrate that careful, science-based adaptive management can be successful for herbicide suppression of invasive weeds in highly sensitive endangered species habitat. The project now serves as a model for responsible weed management and endangered species recovery.