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Title: Potential use of native aquatic plants for long-term control of problem aquatic plants in Guntersville Reservoir, Alabama. Report 1, Establishing native plants
Authors: Aquatic Plant Control Research Program (U.S.)
Doyle, Robert D. (Robert Donald)
Smart, R. Michael.
Keywords: Eurasian watermilfoil
Aquatic plants
Nuisance species
Invasive species
Native species
Native plants
Aquatic vegetation
Guntersville Reservoir
Environmental management
Publisher: Environmental Laboratory (U.S.)
Engineer Research and Development Center (U.S.)
Description: Technical Report
Abstract: The littoral regions of Guntersville Reservoir have a long history of nuisance infestations of Myriophyllum spicatum (Eurasian watermilfoil) and more recently of Hydrilla verticillata (hydrilla), problem species that invade recently disturbed areas. Management strategies have included water level management and chemical treatment of Myriophyllum and introduction of grass carp to control Hydrilla. Both strategies have shortcomings. Chemical treatment can be applied in specific problem-infested sites, but since the entire reservoir conld never be treated, this method does not prevent, and may even promote, the re-invasion of the nuisance species. Grass carp in sufficient numbers effectively prevent re-invasion but provide limited specificity for either site or plant species, and the loss of desirable native submersed plant populations is probable. Recently, there has also been an increase in another nuisance plant, the mat-forming, blue-green alga Lyngbya wollei. Lyngbya mats result in serious, often localized, negative effects on the use of some areas. There are currently no effective chemical or biological control strategies for this organism. A long-term solution to these problems may be the establishment of desirable native aquatic plants in areas subject to colonization by the nuisance species or in areas recently treated by conventional weed control methods. By occupying these areas, native plants may prevent, or at least delay, the regrowth of the nuisance plants. Efforts to establish populations of Potamogeton nodosus and Vallisneria americana in areas historically dominated by Myriophyllum spicatum are currently hindered by heavy herbivore pressure and a total decline of all submersed aquatic plant species in the Chisenhall embayment where this research is being conducted. While the grass carp are effectively excluded from test plots by fencing, plantings within the exclosures attract other herbivores such as turtles, muskrats, and ducks, which are capable of getting into the fenced areas. Success in establishing these two native species in Guntersville Reservoir has been low, and has come at a high price. Potamogeton establishment has required building fenced exclosures and then continued trapping of turtles and muskrats within the enclosed areas. Vallisneria establishment has been even more difficult, requiring that the individual Vallisneria plots within the larger exclosure be fenced as well. Establishment of native floating-leaved and emergent species of macrophytes in Lyngbya-infested areas has been more successful. This research, carried out at two Lyngbya and one control site, has tested the suitability of seven native plant species for establishment in Lyngbya-infestations. Two major conclusions can be drawn. First, by comparing test plots within fenced exclosures and identical unprotected test plots, the absolute necessity of herbivore protection for establishing small populations of native macrophytes at this time is demonstrated. This result is attributed to the apparently high herbivore pressure due to the recent decline in submersed aquatic macrophytes in the reservoir. Second, only three of the seven species tested for establishment were found suitable for growth in Lyngbya-dominated areas. These species, Potamogeton nodosus, Nelumbo lutea, and Pontederia cordata, had morphological characteristics that enabled them to withstand the high degree of mechanical disturbance caused by the continuous movement of the large floating mats of Lyngbya. Four species were found not to be suitable. Eleocharis quadrangulata and Scirpus validus were totally destroyed by the movement of the Lyngbya mats. The rigid, brittle shoots of these plants were broken repeatedly by the Lyngbya movement Movement of the floating mats occurred in both horizontal and vertical directions relative to the macrophyte shoots and was driven by wind and elevational changes in the reservoir. A few individuals of Justicia americana and Saururus cernuus survived in the Lyngbya areas, but the successful establishment of these species is doubtful.
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