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Conservation: Purple Loosestrife


Purple Loosestrife Lythrum salicaria is an exotic wetland plant that has been introduced from Europe and has since exploded into the wetlands of North America.

Anyone planning management or conservation work should first read these two background manuals:


  • Thompson, D.Q., R.L. Stuckey and E.B. Thompson. 1987. Spread, Impact and Control of Purple Loosestrife (Lythrum salicaria) in North American Wetlands. United States Department of the Interior, Fish and Wildlife Service, Washington, D.C. 55 p. Available from Publications Unit, U.S. Fish and Wildlife Service, Washington, DC 20240

  • Keddy, C.J. 1992. A Universal Manual for Purple Loosestrife Control. Ontario Supported by Ontario Heritage Foundation and Wildlife Habitat Canada. 62 pp. plus appendices. Available from Ontario Federation of Anglers and Hunters, P.O. Box 2800, Peterborough, Ontario, Canada K9J 8L5 ($16.00)

Although managers now have a great deal of concern about this species, rather little is known about its ecology. Over the past fifteen years Paul Keddy's research team has accumulated and published an extensive data base on the ecology of L. salicaria. This work is frequently overlooked because of the habit of doing literature searches using only the name L. salicaria. Most of the ecological data in our work involves many species and will not be found using such superficial search techniques. A partial list of the relevant papers follows:

  • Keddy, P.A., L. H. Fraser and I. C. Wisheu. 1998. The competitive response of 48 wetland plants to 7 canopy-forming species. Journal of Vegetation Science 9: 777-786. (effects of a L. salicaria canopy on establishment of 47 other species)

  • Weiher, E., G.D. P. Clarke and P.A. Keddy. 1998. Community assembly rules, morphological dispersion, and the coexistence of plant species. Oikos 81: 309-322. (an ecomorphological analysis of how L. salicaria fits into existing wetland vegetation)

  • Keddy, P.A., L. Twolan-Strutt and B. Shipley. 1997. Experimental evidence that interspecific competitive asymmetry increases with soil productivity. Oikos 80: 253-256. (effects of fertility on competitive effect of L. salicaria seedlings)

  • Weiher, E., I. C. Wisheu, P.A. Keddy and D.R.J. Moore. 1996. Establishment, persistence, and management implications of experimental wetland plant communities. Wetlands 16: 208-218. (ability of L. salicaria to dominate 24 different experimental wetland communities)

  • Twolan-Strutt, L. and P.A. Keddy. 1996. Above- and below-ground competition intensity in two contrasting wetland plant communities. Ecology 77: 259-270. (response of L. salicaria to competition gradients in wetlands)

  • Weiher, E. and P.A. Keddy. 1995. The assembly of experimental wetland plant communities. Oikos 73: 323-335. (spread of L. salicaria to dominate 24 different experimental wetland communities over five year experiment)

  • Gaudet, C.L. and P.A. Keddy. 1995. Competitive performance and species distribution in shoreline plant communities: a comparative approach. Ecology 76(1): 280-291. (effects of interspecific competition on field distribution of plants including L. salicaria)

  • McJannet, C.L., P.A. Keddy and F.R. Pick. 1995. Nitrogen and phosphorus tissue concentrations in 41 wetland plants: a comparison across habitats and functional groups. Functional Ecology 9: 231-238. (includes L. salicaria)

  • Keddy, P.A., L. Twolan-Strutt and I. C. Wisheu 1994. Competitive effect and response ranking in 20 wetland plants: are they consistent across three environments? Journal of Ecology 82: 635-643. (includes L. salicaria)

  • Boutin, C. and P. A. Keddy. 1993. A functional classification of wetland plants. Journal of Vegetation Science 4: 591-600. (L salicaria as a functional annual or gap coloniser)

  • Wisheu, I. C. and P.A. Keddy. 1992. Competition and centrifugal organization of ecological communities: theory and tests. Journal of Vegetation Science 3: 147-156. (a general model for management and conservation of wetland diversity)

  • Shipley, B. S., P.A. Keddy, D.R.J. Moore and C. Gaudet. 1991. A model of species density in shoreline vegetation. Ecology 72: 1658-1667. (includes L. salicaria)

  • Shipley, B. S., P.A. Keddy and L. P. Lefkovitch. 1991. Mechanisms producing plant zonation along a water depth gradient: a comparison with the exposure gradient. Canadian Journal of Botany 69: 1420-1424. (includes L. salicaria)

  • Johansson, M. E. and P.A. Keddy. 1991. Intensity and asymmetry of competition between plant pairs of different degrees of similarity - an experimental study on two guilds of wetland plants. Oikos 60: 27-34. (includes L. salicaria)

  • McCanny, S. J., P.A. Keddy, T. J. Arnason, C.L. Gaudet, D.R.J. Moore and B. Shipley. 1990. Fertility and the food quality of wetland plants: a test of the resource availability hypothesis. Oikos 59: 373-381. (includes L. salicaria)

  • Shipley, B., P.A. Keddy, D.R.J. Moore and K. Lemky. 1990. Regeneration and establishment strategies of emergent macrophytes. Journal of Ecology 77: 1093-1110. (includes L. salicaria)

  • Moore, D.R.J. and P.A. Keddy. 1989. The relationship between species richness and standing crop in wetlands: the importance of scale. Vegetatio 79: 99-106. (includes L. salicaria)

  • Gaudet, C.L. and P.A. Keddy. 1988. Predicting competitive ability from plant traits: a comparative approach. Nature 334:242-243. (L. salicaria the strongest competitor among 44 plant species)

  • Day, R., P.A. Keddy, J. McNeill and T. Carleton. 1988. Fertility and disturbance gradients: a summary model for riverine marsh vegetation. Ecology 69:1044-1054. (distribution of adults and seedlings of L. salicaria during the early stages of its invasion of the Ottawa River)

Other Papers that have included L. salicaria

  • Moore, D.R.J., P.A. Keddy, C.L. Gaudet and I. C. Wisheu. 1989. Conservation of wetlands: do infertile wetlands deserve a higher priority? Biological Conservation 47: 203- 217

  • Keddy, P.A. and B. Shipley. 1989. Competitive hierarchies in herbaceous plant communities. Oikos 54: 234-241.

  • Shipley, B. and P.A. Keddy. 1988. The relationship between relative growth rate and sensitivity to nutrient stress in twenty eight emergent macrophytes. Journal of Ecology 76: 1101-1110.

  • Moore, D.R.J. and P.A. Keddy. 1988. Effects of a water-depth gradient on the germination of lakeshore plants. Canadian Journal of Botany 66:548-552.

  • Shipley, B. and P.A. Keddy. 1987. The individualistic and community-unit concepts as falsifiable hypotheses. Vegetatio 69:47-55.

  • Isabelle, P.S., L.J. Fooks, P.A. Keddy and S. D. Wilson. 1987. Effects of roadside snowmelt on wetland vegetation: an experimental study. Journal of Environmental Management 25: 57-60.

  • Keddy, P.A. and A. A. Reznicek. 1986. Great Lakes vegetation dynamics: the role of fluctuating water levels and buried seeds. Journal of Great Lakes Research 12:25-36.

  • Keddy, P.A. and P. Constabel. 1986. Germination of ten shoreline plants in relation to seed size, soil particle size and water level: an experimental study. Journal of Ecology 74:133-141.

  • Keddy, P.A. and T.H. Ellis. 1985. Seedling recruitment of 11 wetland plant species along a water level gradient: shared or distinct responses? Canadian Journal of Botany 63: 1876-1879.

  • Keddy, P.A. 1983. Freshwater wetlands human-induced changes: indirect effects must also be considered. Environmental Management 4:299-302.

World's Largest Wetlands

Readings on Louisiana

Four Priority Areas for the Protection of Eastern Coastal Plain Ecosystems

Louisiana Conservation Map


Purple Loosestrife

Ottawa Valley

Wetland Ecology

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