Phragmites Grass
Phragmites australis
REPLACEMENT OF
NATIVE NORTH AMERICAN PHRAGMITES AUSTRALIS BY
INTRODUCED INVASIVE GENOTYPES
From: Bernd Blossey [bb22@cornell.edu]
Background
Until recently, botanists, ecologists, and wetland managers were debating whether an important invasive plant, (Phragmites australis (Cav.) Trin. ex Steud.), or common reed, was introduced or native to North America. Peat core analyses suggest that P. australis has been an uncommon member of mixed tidal wetland plant communities in North America for at least 3000 years (Niering et al. 1977, Orson et al. 1987). In the 19th but particularly in the late 20th century, P. australis began invading fresh and brackish wetlands in North America greatly expanding its range and abundance. Mixed wetland plant communities are replaced by near monocultures of P. australis, resulting in changed ecosystem processes and associated detrimental impacts on native wildlife (Marks et al. 1994, Meyerson et al. 2000). The population explosion of P. australis is often thought of being facilitated by changes in land use patterns and hydrologic regimes, increased disturbances, urbanization and eutrophication (Marks et al. 1994). However, the very same factors are thought to cause declines of P. australis n Europe (van der Putten 1997). Alternatively, it has been suggested that the invasiveness of is attributable to introduction of more aggressive European genotypes (Metzler and Rosza 1987, Tucker 1990, Besitka 1996) but until recently little information was available to support this hypothesis. Regardless of the status of P. australis as native or introduced, control attempts are widespread and the search for potential biological control agents has begun in North America and Europe (Tewksbury et al. 2002).
Discovery of native and introduced genotypes using genetic markers
Research by Kristin Saltonstall at Yale University (Saltonstall 2002) has now confirmed the present-day existence of native North American haplotypes (lineages) and of introduced European haplotypes. A total of 27 haplotypes were identified of which 11 (A-H, S, Z, AA) are native to North America (Saltonstall 2002). Within the North American populations, a continuum of geographic substructuring exists for the native haplotypes. Types AA, F, Z and S are known historically from the Northeast; types E, G, and H are found throughout the Midwest; and types A-D are found in the South and Intermountain West only. Two haplotypes show worldwide distribution (I and M) with M as the most common type in North America, Europe, and Asia. Type I is found along the Gulf Coast and also occurs in South America and Asia. (For more details see Saltonstall 2002.)
Comparing the genetic structuring of present-day populations with those available in herbarium specimens collected prior to 1910 reveals significant changes in haplotype frequencies in North America. While the herbarium samples show a widespread distribution of native haplotypes across North America, modern populations show a striking range expansion of the M haplotype (Saltonstall 2002). Type M has entirely replaced native types in New England and expanded to the southeast where no historic P. australis populations were known to occur. Type M (which is most closely related to other European types) has spread to the West and is also becoming prevalent in the Midwest. It is likely that the introduction of type M material has occurred sometimes in the early part of the 19th century, probably at several Atlantic coast ports. Over the last 150 years, among-population variation in North America has declined significantly and today the genetic structure of North American populations resembles that of Europe (Saltonstall 2002).
Discovery of morphological differences between native and introduced genotypes
With the recent discovery of the presence of native and non-native populations of Phragmites in North America we also discovered easy to use morphological characters potentially distinguishing native and introduced genotypes. Preliminary observations of populations in New York, Wisconsin, Virginia, Arizona, and Louisiana as well as examination of numerous her-barium specimens indicate that such morphological differences may exist. Please note that these traits are based on examination of few native clones and need further confirmation. We also need to increase the sample size to assess whether the morphological differences between native and introduced genotypes are consistent across populations and lineages. More details and pictures are provided at: www.invasiveplants.net.
In general, native populations appear to have a lower stem density, thinner more flexible stems, and produce a reddish- purple color on their stems and ligules in spring and summer that is not present in non-native populations. When checking for these differences note that the side of the stems exposed to the sun will show the brightest coloration. The reddish color fades somewhat into a chestnut brown in the fall but was still very obvious in October in Virginia; in the winter the red stems turn light brown and somewhat gray. The ligules of native genotypes are bright purple while ligules of introduced genotypes appear green or slightly yellow. Stems of native genotypes are smooth and shiny as if polished, particularly in the winter, while stems of introduced genotypes are tan and dull, rough and ribbed (ridges visible with the naked eye once the leaf sheath has been removed). These differences are easy to recognize by running your fingers up and down them stems. (Please note that a leaf sheath wraps around the stem almost entirely. It is important to remove the leaf sheath when checking for stem morphology or texture.) In instances where native and introduced clones grow in close vicinity of each other, differences in stem toughness become obvious on windy days. Introduced genotypes remain sturdy and erect and move little while native genotypes easily bend and swing in the wind. Stems of introduced genotypes are almost perfectly straight while stems of native genotypes often grow crooked. In the fall and winter, differences in the density of the inflorescence are also obvious; introduced genotypes appear to have a much denser and larger inflorescence. Observations in New York and Virginia also suggest that native genotypes senesce earlier than introduced genotypes (this is a common phenomenon in introduced species which often show extended growing periods). In addition, an unidentified fungus attacks native genotypes with dark spots often clustered around internodes while introduced genotypes do not show this attack. However, introduced genotypes are frequently attacked by a number of generalist fungi (Tewskbury et al. 2002). However, this attack (visible as large, variable blackish areas) is restricted to leaf sheaths.
We need your help
Our observations are based on few native clones and we need to confirm these morphological differences by examining different genotypes in the field and by growing them under standardized conditions in a common garden. We are currently developing a standardized data record sheet (available by the end of March at www.invasiveplants.net). We are unable to visit sites across North America ourselves and depend on your help to refine our ability to use easily visible field characteristics to identify native and introduced genotypes. We are particularly interested in:
1. Locations of native genotypes across North America. It appears that most native populations in the East have vanished or have been overrun by introduced genotypes. For genotype-specific management it will be important to record the presence of native genotypes.
2. Information about presence/absence of field characteristics as outlined above or of any other additional traits that may help discriminate among native and introduced genotypes.
3. Seed collections from native and introduced genotypes from as many different regions as possible. This will allow us to establish germination trials to better understand the differences in competitive ability of native and introduced clones.
4. Rhizome collections from as many native and introduced genotypes as possible. We need approximately 1-2 pounds of rhizome material to establish a common garden.
5. Stem collections (in the dormant season) to assess differences in insect herbivores attacking native and introduced genotypes. We have preliminary evidence from stands in New York that the insect communities in introduced and native genotypes differ significantly. We are currently developing standardized sampling protocols. These protocols will be posted on the web and we hope that many of you will be able to contribute to this important work. For immediate questions, to obtain instructions for collections or advice please contact bb22@cornell.edu.
The work outlined above is a collaboration of the Biological Control of Non-Indigenous Plant Species Program at Cornell University, Kristin Saltonstall at Yale University, and the University of Rhode Island. For further information or updates please visit: www.invasiveplants.net.
References:
Besitka, M.A.R. 1996. An ecological and historical study of Phragmites australis along the Atlantic Coast. M.Sc. thesis. Drexel University, Philadelphia, PA.
Marks, M., Lapin, B., and Randall, J. 1994. Phragmites australis (P. communis): Threats, management, and monitoring. Natural Areas Journal 14: 285-294.
Metzler, K., and R. Rosza, R. 1987. Additional notes on the tidal wetlands of the Connecticut River. Newsletter of the Connecticut Botanical Society 15: 1-6.
Meyerson, L. A., K. Saltonstall, L. Windham, E. Kiviat, & S. Findlay. 2000. A comparison of Phragmites australis in freshwater and brackish marsh environments in North America. Wetlands Ecology and Management 8: 89-103.
Niering, W. A., R. S. Warren, and C. Weymuth. 1977. Our dynamic tidal marshes: Vegetation changes as revealed by peat analysis. Connecticut Arboretum Bulletin # 22.
Orson, R. A., R.S. Warren, & W.A. Niering. 1987. Development of a tidal marsh in a New England river valley. Estuaries 10: 20-27.
Saltonstall, K. 2002. Kryptic invasion by non-native genotypes of the common reed, Phragmites australis, into North America. Proceedings of the National Academy of Sciences of the United States of America 99: 2445-2449.
Tewksbury, L. T., R.A. Casagrande, B. Blossey, M. Schwarzlaender, & P. Haefliger. 2002. Potential for biological control of Phragmites australis in North America. Biological Control 23: 191-212.
Tucker, G. C. 1990. The genera of Arundinoidae (Gramineae) in the southeastern United States. J. Arnold Arboretum 71: 14- 171.
Van der Putten, W. 1997. Die-back of Phragmites australis in European wetlands: an overview of the European research program on reed die-back and progression (1993-1994). Aquatic Botany 59: 263-275.
Author's address:
Bernd Blossey
Department of Natural Resources
Fernow Hall, Cornell University
Ithaca, NY 14853
USA email
bb22@cornell.edu
Web:
www.invasiveplants.net
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