Background Information

Perennial pepperweed, Lepidium latifolium, is a highly invasive perennial herb that can thrive in a wide range of habitats including riparian areas, wetlands, marshes, and floodplains (Bossard et at. 2000; Young et al. 1995). Once established this plant creates large monospecific stands that displace native plants and animals and can alter soil composition by concentrating salts at the surface (Young, Turner et al. 1995; Renz and DiTomaso 1998). Due to its highly invasive nature it is on the A-list of the California Invasive Plant Council’s (CALIPC) list of Exotic Pest Plants of Greatest Ecological Concern in California, and on the California Department of Food and Agriculture’s B list of noxious weeds. This plant is a priority for control efforts not only because of its highly invasive nature and the threat it poses to native habitats but also because potential for its control is considered high.

In the Cosumnes River Preserve, Lepidium has emerged as the invasive plant of most concern in its restoration projects. The Cosumnes River Preserve (CRP) serves as a model of habitat conservation and floodplain restoration in the Central Valley. Scientists in the Cosumnes Research Group I and II (CRG) (CALFED grants #1999-NO6, #2000-FO8, #2001-NO1) and on CRP staff are studying changes in hydrology, vegetation, and aquatic and terrestrial biota that are occurring in response to natural and man-made breaches to levees along the Cosumnes River within preserve boundaries. The Nature Conservancy, on behalf of all of the partner land managers in this Preserve (including the Bureau of Land Management, Department of Fish and Game, U.S. Fish and Wildlife Service, Duck’s Unlimited, Sacramento County, and a number of local farmers and ranchers) is planning an aggressive program of Lepidium control. However, the available science for choosing the best control strategy is limited, despite the importance of the plant throughout the Delta region and on many other restoration sites. As a result, this project of research and adaptive management, builds on two CALFED and Packard Foundation-funded Cosumnes Research Group (CRG) projects. Research and monitoring at these passive and active restoration areas in the Cosumnes River Preserve is providing valuable data that can be used to inform future restoration activities in the CBDA region. The purpose of this project is to continue the established partnership between the Cosumnes River Preserve (CRP) and the UC Davis Information Center for the Environment (ICE), complementing ongoing Cosumnes research by performing an intensive study of the most rapidly expanding invasive plant in the Cosumnes study area, Lepidium latifolium. This project will be conducted solely on property of the Cosumnes River Preserve, and does not include a public participation component.

Primary Project Goal

This research will develop strategies and an adaptive management framework for the control of Lepidium latifolium at the Cosumnes River Preserve. The approach for this project closely follows the Adaptive Management of Invasive Species (CALFED workshop, Davis, July 2003), and represents a pilot-species, pilot-region application of a general framework to experimentally develop control strategies for terrestrial invasives that can be used to inform future restoration activities in the CALFED region.

Study Objectives

This project will address several scientific needs of the ERP via targeted research and pilot projects regarding adaptive management and monitoring of weed control efforts in general and Lepidium specifically. Inventory and continued monitoring of existing Lepidium populations at the Cosumnes River Preserve will provide the background data necessary to statistically analyze population change as adaptive management projects proceed (Objective 1). Targeted research on control of Lepidium will use a scientific hypothesis-testing approach to refine our conceptual model and guide adaptive management actions (Objective 2). This research is explicitly designed to add to existing knowledge about relationships between management techniques and ecosystem structure and function by testing current hypotheses concerning weed control and ecosystem restoration. Results will then be used in an adaptive management framework to guide full-scale implementation of Lepidium management at the Preserve, as well as being incorporated into a framework for meta-analysis of related projects in the CALFED region (Objective 3).