Landscape-level assessment of native and non-native Phragmites australis within marine and mainland source watersheds and evaluation of island/marsh restoration efforts on Virginia's Eastern Shore

Background/Question/Methods

Over the past two decades, the distribution of the invasive wetland grass, Phragmites australis has rapidly spread into coastal habitats throughout the Northeast and mid-Atlantic regions, including the Delmarva Peninsula. A distinct, non-native Phragmites genotype has been aggressively invading and dominating coastal wetland communities.  However, native Phragmites stands are as susceptible to preemption and local extirpation from non-native Phragmites as are other indigenous coastal wetland species. In addition, Phragmites invasion has complicated coastal restoration and reclamation projects.  To assess Phragmites invasion characteristics, 80 patches were selected within 8 marine watersheds and their adjacent mainland source watersheds along the seaside of the Eastern Shore of Virginia. 

Results/Conclusions Phragmites patch size ranged from approximately 15 m² to > 25,000 m².  All sampled Phragmites patches were classified as non-native, based on plant morphological characteristics examined in the field and in the laboratory.  Percent cover was variable, but almost half of the patches had 75 to 100 % Phragmites cover. Most native species were reduced or eliminated. Revegetation efforts on two marsh islands formerly dominated by Phragmites were monitored in 1998, 2000 and 2005.  Species richness of naturally colonizing herbaceous plants has declined by 50% over the past 8 years.  However, species richness of planted trees and shrubs has remained the same.  Although the frequency of sampled shrubs has decreased, the surviving planted woody species are exhibiting vigorous growth ranging in size from 1.5 to over 3 m in height.  Fruit production was observed on approximately half of the Morella species shrubs and 35 % of all trees and shrubs contained bird nests, indicating that passerine birds are using these sites for reproduction.  After 8 years of revegetation, Phragmites is still the most abundant species on these restored sites.  However, plant species diversity and structural diversity have increased and should increase the diversity of wildlife within these sites. Determination of native vs. non-native Phragmites coupled with evaluating restoration attempts of Phragmites impacted coastal habitats is critical from a management perspective especially in planning and evaluating the efficacy of current Phragmites control methodologies and future habitat rehabilitation efforts.