Restoration and management of Ludwigia hexapetala-invaded wetlands of the Laguna in the face of climate change.

Publication Type  Conference Presentation
Authors  Brenda J. Grewell; Caryn J. Futrell
Affiliations  USDA-ARS Exotic & Invasive Weeds Research Unit, Dept of Plant Sciences MS-4, University of California, Davis, California 95616
Year  2009
Key Words  Ludwigia hexapetala; invasion ecology; aquatic weed; integrated weed management; nutrient cycling; wetland restoration; seed bank

The successful invasion of the Laguna de Santa Rosa by Ludwigia hexapetala (Uruguayan primrose-willow) has challenged watershed goals for restoration of desirable biological communities and ecosystem processes. The abundance of aquatic weeds is regulated by light, hydrology, temperature, nutrients, and biological interactions that may all vary with climate. In South America, L. hexapetala withstands highly fluctuating environmental conditions of a flood-pulse river system. As an exotic weed, L. hexapetala thrives in a broader range of climatic conditions than those experienced in its native range. Management of L. hexapetala requires knowledge of its tolerance to a range of conditions beyond those locally observed. We experimentally evaluated the growth, nutrient allocation and cycling dynamics of L. hexapetala in the Laguna and Russian River. While these factors varied across observed gradients, this weed is well adapted to both high and low resource environments and to variable hydrologic conditions. Our evaluation of integrated methods for control of L. hexapetala in canals and wetlands show promise, yet research suggests that as atmospheric CO2 levels rise, weeds will be harder to control and efficacy of herbicides will be reduced. Seed banks contribute to wetland community maintenance and to succession following disturbances imposed by weed control actions. Knowledge of how recruitment mechanisms change with environment is essential for weed management. We compared differences in standing vegetation and seed banks among invaded and non-invaded sites within the Laguna, using a seedling emergence assay to determine the reinvasion potential of L. hexapetala, to reveal cryptic taxa, and to test emergence response to inundation regime and sedimentation. Over 12 months, 69 taxa germinated from seed banks including L. hexapetala and several other undesirable weeds. Results signal the need for persistent management to deplete weed seed banks, and for the implementation of comprehensive weed management strategies to meet restoration goals.


Brenda Grewell is a research ecologist with the USDA-Agricultural Research Service’s Exotic & Invasive Weed Research Unit at the University of California, Davis. The focus of her program is to understand mechanisms controlling the dynamics of aquatic and riparian plant communities and promoting the invasion of exotic species to identify key factors that must be overcome for successful integrated weed management and restoration. Dr. Grewell holds a Ph.D. in Ecology from the University of California, Davis. As a Fulbright Fellow in the Czech Republic, she studied the ecological variation of invasive purple loosestrife in its native European range. She has a broad background in wetland ecology and conservation biology, and has been investigating relationships between water management, aquatic/wetland plant ecology, and ecological restoration for more than 20 years. Her current focus primarily is on the ecology of invasive water primrose-willows (Ludwigia sp.) from South America that are aggressively invading rivers, canals, rice fields, and sensitive wetland habitats of Pacific west coast states.

Conference Name  2009 State of the Laguna Conference and Science Symposium
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