Effects of abiotic factors on the life span of the invasive cordgrass Spartina densiflora and the native Spartina maritima at low salt marshes

摘要

We analyzed variations in the life span of the invasive cordgrass Spartina densiflora at low marshes of SW Iberian Peninsula, and identified the abiotic factors limiting the plant in the absence of competition. With these objectives, clump survivorship, flowering, and growth of S. densiflora were studied in two natural populations at different low marsh elevations during more than three years, and at a transplant experiment in comparison with the native Spartina maritima. The life spans of both cordgrasses changed depending on small variations of a few centimeters in elevation. S. maritima, which tolerates better than S. densiflora the stressful abiotic environment of lower marshes, showed a significant lower distribution limit for its perennial habit, with survivorship longer than three years (from 1997 to 2000), than the neophyte (+1.57 m SHZ vs. +2.00 m SHZ). S. densiflora clumps flowered before dying at mostly all elevations, showing low relative growth rates. In contrast, clumps of S. maritima, with non-viable seeds, only flowered when they were three years old at higher elevations in the low marsh. Our results have applications for salt marshes bioengineering projects and to prevent S. densiflora from invading European marshes since our data improve the knowledge of its colonization mechanisms through salt marsh zonation and so identify those portions of restored and native marshes most susceptible to invasion due to the establishment of perennial populations.