Factors Affecting Reestablishment of an Endangered Annual Plant at a California Salt Marsh

Abstract

We asked whether the reproductive capacity of the endangered Cordylanthus maritimus ssp. maritimus (salt marsh bird's-beak) at Sweetwater Marsh (San Diego Bay, California) was sufficient to provide a self-sustaining population, as required by a mitigation agreement under the Endangered Species Act. After seeds were sown for three consecutive years (1990)(1991)(1992) to an upper intertidal marsh where the historical population was last seen in 1987, the number of plants censused rose from ഠ5000 in 1992 to ഠ14 000 in 1995.The transplanted population initiated fewer seed capsules per flower (mean 0.2-0.4 capsules in 1992-1994) than the donor population (up to 0.9 capsules in 1991). Pollen supplementation (hand-pollination) treatments increased the number of capsules by 89% in 1992, and by 52% in 1993. Abundance of pollinators appeared to be less important than the relative abundance of particular genera (i.e., Anthidium and Bombus). However, in areas where pollen supply was sufficient, nitrogen availability seemed to limit capsule set.Plant growth rates of the transplanted population compared favorably with those of the donor population (mean height 12-13 cm). At Sweetwater Marsh, larger plants produced more flowers, and aboveground dry mass of plants correlated strongly with inorganic nitrogen in the soil, which was Ͼ71% sand. Nitrogen fertilization treatments increased plant size, foliar nitrogen content, and mean seed mass.Even though the population produced Ͼ1.5 ϫ 10 6 seeds from 1992 to 1994, it is not clear that C. m. maritimus will be able to sustain itself at Sweetwater Marsh. The number of plants in 1994 was Ͻ3% of the estimated seed production in 1992-1994. Opportunities for seed germination and seedling establishment may be more limiting than reproductive capacity. The most difficult challenge to habitat managers may be maintaining ecological relationships that are dependent on external factors, i.e., pollinators, nutrient inflows, and canopy disturbances (from debris or mammals) that create the necessary openings for seedling recruitment.

A broader ecological context to habitat fragmentation: Why matrix habitat is more important than we thought

“…For instance, reduced pollinator communities due to urbanization of the surrounding landscape were suspected to cause significant seed set reduction in a reintroduced population of an endangered salt marsh plant in California, where hand pollination of Cordylanthus maritimus ssp. maritimus increased seed capsule set by 89% in 1992 and 52% in 1993 (Parsons & Zedler 1997; note these hand pollinations could only be conducted at one site). Such substantial effects on reproduction would quite likely have strong impacts on population health, but they may even impact the evolutionary trajectories of plant populations.…”

Directing Spatial Patterns of Recruitment During an Experimental Urban Woodland Reclamation

“…Simply boosting dispersal could therefore prove insufficient to accelerate woodland succession, without taking steps to identify potential safe site limitations (Harper 1977), to test their relative effects and to ameliorate the most influential limiting factors. In some cases, the plants chosen for reclamation may improve site properties, such as nutrient mineralization (Bradshaw and Chadwick 1980), while in others site preparation requirements may include manipulating the substrate to ensure abundant safe sites (Parsons andZedler 1997, Urbanska 1997).…”

Genetic Variation and the Reproduction of Cordylanthus maritimus ssp. maritimus to Sweetwater Marsh, California

“…maritimus is an annual, facultatively hemiparasitic species of coastal salt marshes (Vanderwier & Newman 1984). It is bee-pollinated, selfcompatible, and weakly autogamous (Lincoln 1985;Parsons & Zedler 1997). Seeds are viable for more than one year, and dispersal occurs by water.…”