We investigated the potential for an invasive sea lavender, Limonium ramosissimum subsp. provinciale (Algerian sea lavender; LIRA) to spread in San Francisco Estuary (SFE) tidal marshes by testing how two determinants of tidal marsh plant distribution, salinity and inundation, affect LIRA dispersal, germination, growth, and reproduction. Simulating dispersal in 0, 15, and 30 parts per thousand (ppt) salinity water, we found seeds remained afloat similarly regardless of salinity, and seed viability after floatation was high (88%); however, seeds in 0 ppt aquaria germinated after just 4 d, suggesting shorter dispersal distances in fresh than in brackish or saline water. Next, we compared LIRA and native halophyte seed germination in 0, 15, 30, and 45 ppt water. Percentage of germination was similar between species after 3 wk, but LIRA germinated faster in fresh water than all native species (90% vs. 5% germination after 4 d), suggesting a possible establishment advantage for LIRA at low salinities. Finally, we grew LIRA under crossed salinity and inundation levels in a tidal simulator for a growing season. LIRA growth and seed production increased when either salinity or inundation was reduced. We conclude that spread could be greatest among salt marshes due to high potential for seed dispersal in saline water, yet spread within marshes may be greatest in relatively lower salinity conditions where growth and reproduction are maximized.
Nomenclature: Algerian sea lavender, Limonium ramosissimum (Poir.) Maire subsp. provinciale (Pignatti) Pignatti.
Management Implications: Information regarding the potential for newly introduced nonnative species to invade wildland ecosystems is needed for resource managers to prioritize responses to multiple simultaneous plant invasions. Management decisions, such as which species or populations to prioritize for eradication or seed suppression, are aided by research that addresses how variation in environmental conditions affects a species' spread. This is true in tidal marshes of the San Francisco Estuary (SFE) where several invasive plants have been identified as priorities for management action because of their rapid spread and impacts, and where new nonnative species continue to establish, many with unknown potential for widespread invasion. This research provides timely information regarding how the spread of an invasive plant recently found in the SFE, Algerian sea lavender, is affected by two key environmental factors that vary within and among tidal salt marshes: salinity and inundation. Investigating the effects of these variables on key life history stages of Algerian sea lavender (dispersal, germination, growth and reproduction) permitted characterization of conditions where Algerian sea lavender propagule pressure will be greatest, and may serve as a model for predicting spread of other nonnative plants across a complex environmental gradient.