Gene M. Silberhorn

Vegetative community structure of a tidal freshwater swamp in Virginia

The vegetative community structure of a tidal freshwater swamp in Virginia was analyzed during August and September of 1979. The ecosystem combined the characteristics of both a wet forest and a marshland, some areas being fully one or the other. The dominant trees of the swamp were clearlyFraxinuspennsylvanica andNyssasylvatica. These two species, together withCarpinuscaroliniana andAcerrubrum, the most important subordinates, comprised 96% of the trees sampled. The herbaceous understory vegetation was similar in composition to that of neighboring marshes, yet with fewer dominant species and individuals. Characteristic of the marshes, the structure of the ground cover varied from month to month as some species initiated new growth while others began to senesce. Consequently there were shifts in the relative importance of the herbs from August to September, even among the more common species, such as:Carexstricta,Polygonumarifolium,Saururuscernuus,Leersiaoryzoides,Impatienscapensis, andPeltandravirginica. The most abundant herb,Aneilemakeisak, far outranked the other species in importance during both months of sampling. Several species of shrubs and vines were also present in the swamp, but they comprised only a minor portion of the vegetative community.

Production of reproductive shoots, vegetative shoots, and seeds in populations ofRuppia maritima L. from the Chesapeake Bay, Virginia

The production of reproductive shoots, vegetative shoots, and seeds was characterized forRuppia maritima populations in the Virginia portion of Chesapeake Bay in 1988 and 1989. The study locations included two previously unvegetated sites recently colonized byR. maritima in the Rappahannock River and an established site and an irregularly flooded marsh panne site, both in the York River. A corer was used to collect plant material, which was then separated into reproductive shoots, vegetative shoots, and seeds. Sampling took place at approximately 2-week intervals from the time of first observation of flowering shoots until reproductive senescence. Reproductive shoot and seed production were high for all sites, particularly the previously unvegetated sites. The percent of reproductive shoots ranged from less than one percent to 52 percent. One previously unvegetated site produced 23,390 seeds m−2 in 1988, the highest level of seed production measured during this study. Dramatic decreases in production from 1988 to 1989 at two of the study locations, the salt panne and one previously unvegetated site, are attributable to the effects of drought and cownose ray (Rhinoptera bonasus) activity, respectively. High levels of seed production, frequently above 20,000 seeds m−2, and their eventual dispersal may account for the rapid colonization in certain areas of Chesapeake Bay byR. maritima.