Name:
Phragmites australis Tidal Herbaceous Alliance
Reference:
Southeastern Ecology Working Gro...
Description:
This alliance includes both natural and invasive fresh to brackish tidal marsh communities dominated by (often essentially monospecific) Phragmites australis. Although Phragmites australis rhizomes have been noted in salt marsh sediments exceeding 3000 years in age and it is thus a native component of salt marshes in some areas of North America, the growth habit of the species in its native condition was likely to have been significantly different than the dense monotypic, invasive stands documented in this alliance. Evidence suggests that a new, more invasive genotype of Phragmites australis was introduced to the U. S. from the Old World. This new genotype, along with a continued increase in and variety of disturbances, may explain the heightened invasiveness of this species. Evidence suggests that along the Gulf Coast of Louisiana and Texas, the genotype found in invasive communities differs from the genotype found in natural, stable communities. Although invasive and natural communities of Phragmites australis are difficult to differentiate, this can be accomplished by considering the degree of disturbance at a site and observing a given stand over time to determine the degree of invasiveness. Based on observations of this nature by individuals familiar with the coastal marshes of Louisiana and Texas, apparently stable, natural communities dominated by Phragmites australis are present. However, the dominance of Phragmites australis in many tidal wetlands today often indicates human-induced disturbance, either through direct habitat manipulation or through passive introduction of reproductive material to naturally disturbed substrates. In many areas of the southeastern United States, it is well documented that Phragmites is recently introduced and spreading rapidly in tidal and non-tidal situations. In invasive communities, associated species are highly variable, depending on the vegetation that has been invaded. Spreading in large colonies, Phragmites may eventually dominate disturbed areas at coverage up to 100%. More typically, though, scattered individuals of other species may occur, such as sparse Morella cerifera (= Myrica cerifera) shrubs, Kosteletzkya virginica, Calystegia sepium, Boehmeria cylindrica, Typha angustifolia, Apocynum cannabinum, Rosa palustris, Polygonum sp., and Mikania scandens. Vines of Toxicodendron radicans are also frequent, but typically occur at low cover. In areas where Phragmites australis is highly invasive, if Phragmites australis is a significant component of the vegetation but the vegetation retains sufficient species composition to retain its identity, the site is considered an unhealthy or degraded example of that vegetation type. In these same areas, if Phragmites australis cover is so high that native species have been excluded and the original community is no longer recognizable, then the occurrence falls within an invasive association within the Phragmites australis Tidal Herbaceous Alliance (A.1477). In natural communities, associated species may include Sagittaria platyphylla, Spartina alterniflora, Schoenoplectus americanus (= Scirpus americanus), Vigna luteola, Typha spp., and others.
Accession Code:
VB.CC.21901.PHRAGMITESAUSTR
Plot-observations of this Community Concept:
0
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