Dr. Scott Petrie, Long Point Waterfowl Executive Director
Dr. Dave Ankney, University of Western Ontario
Phragmites australis is a large perennial rhizomatous reed that competes with other wetland plants. While it has coexisted with North American plants for over 3,000 years, it has expanded rapidly over the last few decades. Although Phragmites stands provide important habitat for several wildlife species in Europe, the effects of large invasive Phragmites stands on lower Great Lakes wildlife has not yet been investigated. Rapid expansion of monotypic Phragmites stands may change the structure and function of lower Great Lakes coastal marshes. Thus, habitat availability and/or suitability may be compromised for many wetland dependent wildlife species, some of which may already be threatened. Further, the recent expansion of an exotic genotype of Phragmites australis throughout many coastal wetlands of the lower Great Lakes has caused concern that it will reduce floral and faunal biodiversity. Few studies, however, have actually documented use of exotic Phragmites stands by wildlife.
In order to make informed management decisions regarding the spread of Phragmites australis at Long Point, it was necessary to evaluate wildlife use of Phragmites and adjacent wetland habitats. Doing so enabled us to determine if the spread of Phragmites was compromising the suitability of coastal marshes for certain species of birds, mammals or amphibians. Thus, during 2001 and 2002, we surveyed the bird, amphibian, and small mammal communities in various-sized stands of Phragmites, Typha spp., and marsh meadow.
During spring 2001, 55 survey stations at 3 study areas (Crown Marsh, Long Point Provincial Park, & Long Point Company), were set up to monitor bird habitat-use.
Each 25 m radius station was placed ³ 50 m from the marsh edge and ³ 250 m from other stations. Observations, made by standing on a
step-ladder, consisted of 5 minutes of song broadcast and 5 minutes of listening/observing. Each station was sampled 6 times annually during the summer, 2 times during the fall and winter, and once during the spring (see Meyer 2003).
Pitfall traps were used to quantify amphibians and small mammals within each of the habitat types at the 3 study areas. One trap line, with £ 5 pitfall traps, was set up within each habitat type. A trap line consisted of a line transect through the habitat type, in which the first pitfall trap was placed 3.5 m from the edge and subsequent traps were placed 20 m apart. Trapping was conducted between early May and late July each year.
Avian point counts showed that stands of exotic Phragmites had fewer rails, waterfowl, and breeding swamp sparrows (Melospiza georgiana) than did stands of Typha or marsh meadow. Large stands of exotic Phragmites, however, had a high abundance of Red-winged Blackbirds (Agelaius phoeniceus) and Common Yellowthroats (Geothlypis trichas) and provided habitat for Least Bitterns (Ixobrychus exilis), swallows (Family Hirundinidae), juvenile Swamp Sparrows, and Marsh Wrens (Cistothorus palustris). Use of exotic Phragmites by Virginia (Rallus limicola) and Sora rails (Porzana carolina) was limited to stand edges. Stand interiors of exotic Phragmites were used by Red-winged Blackbirds, Common Yellowthroats, and Tree Swallows (Tachycineta bicolor). Stands of exotic Phragmites did not affect migrating birds and may provide winter shelter for Black-capped Chickadees (Poecile atricapillus), American Tree Sparrows (Spizella arborea), and Dark-eyed Juncos (Junco hyemalis).
Pitfall traps showed that Fowlers toads (Bufo woodhousii fowleri) did not use large stands of exoticPhragmites and use by northern leopard frogs (Rana pipiens) was limited. Small stands of exoticPhragmites had more amphibians [primarily juvenile toads (Bufo spp.)] than did small stands of Typha and marsh meadow in mid-summer. Interior traps in large stands of exotic Phragmites had fewer amphibians than did edge traps in Phragmites and traps in Typha and marsh meadow. Species richness of amphibians, however, was similar in all three habitats. Overall, all small stands, regardless of habitat type, had more individuals and higher species richness of amphibians than did large stands.
Although only four species of small mammals were captured, large stands of exotic Phragmites had higher abundance and species richness of small mammals than did large stands of Typha and marsh meadow.
Conclusions & Implications
Continued expansion of large stands of exotic Phragmites in coastal marshes at Long Point may negatively affect Swamp Sparrows, rails, waterfowl, northern leopard frogs, and Fowler’s toads, but may benefit Least Bitterns, Red-winged Blackbirds, warblers (Family Parulidae), meadow voles, and shrews. However, given the current distribution of exotic Phragmites stands at Long Point and its current rate of expansion (50 % per year; Wilcox et al., 2003), management options may be warranted in order to preserve habitat heterogeneity. Because this study was conducted during low water levels, we recommend that studies continue to investigate use of Phragmites by vertebrates, particularly waterfowl, rails, bitterns, Fowler_s toads, green frogs, and bullfrogs during higher water levels. These studies, in conjunction with a management strategy focused on interspersion of habitats, will maintain wetland integrity at Long Point and increase understanding of the effects of Phragmites expansion on these animals.