Reestablishment of Native Plants in Roger Williams Park Zoo Wetland,

1. Reestablishment of Native Plants in Roger Williams Park Zoo Wetland, after Biological Control of Purple Loosestrife, Lythrum salicaria. Lisa Tewksbury, Richard Casagrande, University of Rhode Island, Plant Sciences Dept. Charles Carberry, Cleanscape 1997 1998 2000 ABSTRACT Purple Loosestrife, Lythrum salicaria, is an introduced invasive wetland plant that out-competes native wetland plants. A biological control program using leaf-feeding beetles, Galerucella spp., was initiated against Purple Loosestrife in the Roger Williams Park Zoo wetland in 1996. In 1998 the loosestrife experienced 100 percent defoliation. From 1996 to 2004 we documented the decline of the Purple Loosestrife population and the reestablishment of native plants. The Purple Loosestrife stands have declined in stem height, the area covered and the amount of flower and seed production. In 2004 the wetland had a number of native plants in abundance which were not common in 1996: Sensitive Fern, Arrowwood Viburnum, Elderberry, Pussy Willow, Arrow Arum, Joe-Pye-Weed, and Swamp Azalea. MATERIALS AND METHODS Three thousand Galerucella calmariensis and Galerucella pusilla beetles were released in the Roger Williams Park Zoo wetland in 1996. We checked square meter quadrats at release sites each year from 1996 to 2002. We measured the height of the five tallest stems in the spring when the beetles were present (late May to early June). We counted inflorescences on the five tallest stems in late September. We also kept a photographic record near the release sites, using the same location on the boardwalk to take each photograph, and taking the photographs at the same approximate time of year (late July to early August) during Purple Loosestrife bloom. Arrow Arum Sagittaria latifolia Swamp Rose-Mallow Hibiscus moscheutos var. palustris RESULTS The beetles successfully over wintered and were established after the first release. We documented a decline in the average stem height after 1998, though leveling off after 2000, and also a decline in the average number of inflorescences. Purple Loosestrife Lythrum salicaria Jewelweed Impatiens capensis Slender Blue Flag Iris Iris prismatica Sensitive Fern Onoclea sensibilis INTRODUCTION Purple Loosestrife was introduced into North America from Europe in the 1800’s. It has since become a serious invasive wetland weed. In 1996 the Roger Williams Zoo began a biological control program in the zoo’s wetland in cooperation with the University of Rhode Island, because the loosestrife was displacing native plants and animals and was difficult to manage. Leaf-feeding beetles, Galerucella spp., were released to feed on the Purple Loosestrife. Purple Loosestrife Stem Height (cm) Purple Loosestrife Inflorescences Elderberry Sambucus canadensis Arrowwood Viburnum Viburnum dentatum Wood Ducks Aix sponsa DISCUSSION As the Purple Loosestrife has declined, many native plants have begun to thrive. There are pioneer species that existed within the soil strata and have made a comeback, such as Arrow Arum, Swamp Rose-Mallow, Jewelweed, Slender Blue Flag Iris, and Sensitive Fern. Other native plants were introduced by the zoo staff, like Elderberry, Arrowwood Viburnum, Bayberry, and Swamp Maple, and the removal of the loosestrife has helped them take hold. Native animals have also benefited from the decline of the loosestrife. Wood ducks and muskrats were absent from the wetland in 1996, but started coming back in 1999. 2003 1999 2004 2003 From 1997, when the beetles had just begun to feed on the Purple Loosestrife, to 2004 there was a noticeable decline in the height and density of Purple Loosestrife in the wetland (above). The clumps of loosestrife roots and dead stems have decreased in size, and there is more open water in the pond (below). Galerucella spp. adult, eggs, and larvae. Acknowledgements: We would like to thank the Roger Williams Park Zoo for their cooperation on this project, and the many student employees in the URI Biological Control Lab who assisted in data collection over the years. This work was partially funded by the RI DEM, and USDA APHIS PPQ. Purple Loosestrife defoliated by Galerucella spp. Roger Williams Zoo Wetland Sign “ Beetles to the Rescue”