PARENT SESSION
Oral Session #88: Wetland Ecology.
Presiding: K. Ewel
Thursday, August 8. 1:00 PM to 3:45 PM. Gila Meeting Room, TCC.
Distribution and vegetation of wax myrtle (Myrica cerifera) thickets in a Louisiana freshwater floating marsh.
BATTAGLIA, LORETTA*,1, DENSLOW, JULIE1,2, HARGIS, THOMAS3, 1 Louisiana State University, Baton Rouge, Louisiana2 USDA Forest Service, Hilo, Hawaii3 Coastal Monitoring, Inc., Lafayette, Louisiana
ABSTRACT- The actinorhizal shrub Myrica cerifera invades freshwater floating marshes (flotant) along the coast of Louisiana. One of the few woody invaders of floating marsh, M. cerifera can form thickets with shaded understories and high nitrogen levels in the organic floating mat that anchors its roots. Previous studies using historic aerial photographs suggest a cyclic pattern of expansion followed by decline that may be attributed to inundation of the mat. Using an established 500 x 250-meter grid, we surveyed vegetation in the marsh and forest-marsh ecotone at Jean Lafitte National Park to determine the distribution of M. cerifera and its relationships with other species. Cover and basal diameters of woody species were measured in eight supplemental thicket plots. A total of 67 species was found, and M. cerifera was present in 70% of the 214 grid plots. Ordination of these plots showed a range of assemblages including oligohaline (Spartina patens) marsh, freshwater herbaceous (Panicum hemitomon and Sagittaria lancifolia) marsh, freshwater scrub-shrub (M. cerifera), and patches of remnant forest (Taxodium distichum). Thickets of M. cerifera, frequently interspersed with freshwater herbaceous species, were restricted mostly to interior flotant between oligohaline marsh fringing Lake Salvador and the edge of the bordering swamp. The shrub was also found in low abundance in isolated non-floating forest patches. Compared to plots with sparse canopies, thickets differed in composition and had lower vascular species richness and higher bryophyte cover. Thickets contained several herbaceous species that were not found elsewhere in the marsh. The exotic tree Sapium sebiferum, common along the spoilbanks of nearby canals, was found almost exclusively in patches of M. cerifera. Our study suggests that establishment of M. cerifera may alter local patterns of species composition and facilitate invasion of S. sebiferum.
KEY WORDS: marsh, invasive species, Myrica cerifera, Sapium sebiferum