VEGETATION EVALUATION
Changes in the composition of marsh vegetation can be an indication that the hydrology of the marsh is changing. Increases in the amount of impervious surface in an urbanizing estuary watershed will cause an increase in freshwater runoff into the estuary. In addition, tidal restrictions such as road crossings on the seaward side of a salt marsh will reduce the amount of salt water carried into the marsh by tidal flows. The combined effects of these two processes include a decrease in the salinity of the salt marsh and the creation of a growing environment that is more favorable to plants that inhabit brackish wetlands (Bryan, 1999).
Among the more opportunistic plant species that can spread into a marsh affected by decreasing salinity levels is an invasive form of Phragmites. Phragmites is a tall (5-15 feet) plant that has a plume-like top and habit of growing in dense, single-species stands. Characteristic of invasive plant species, Phragmites will crowd out native marsh plants and cause a significant change in the plant community. It is especially common in brackish wetlands and is able to quickly colonize areas of bare, wet soil that has been stripped of existing vegetation (Bryan, 1999). Accordingly, it is often seen in roadway ditches and drainage systems.
The threat that decreasing salinity and the associated proliferation of Phragmites poses to Scarborough Marsh has been well-documented in previous studies (Linnell, 1994) (Bryan, 1999). In an effort to continue monitoring the spread of Phragmites in the Libby River Watershed, the Friends determined that it would be appropriate to note the locations of Phragmites that were observed during the course of the watershed survey. Although it is far from being a complete assessment of the distribution of Phragmites in the watershed, it does give an indication of the areas that the plant is invading and can be used as a starting point for future monitoring.
Phragmites was observed in the areas shown in Figure 10 during the course of the survey. Most of the areas are on the inland side of the Black Point Road crossing. The following types of habitat are associated with these areas:
The above list of habitats indicates that the spread of Phragmites is influenced by activities that have disturbed soil and/or vegetation. This is entirely consistent with this plant’s history of exploiting environments where development has altered the landscape.