Managing invasive plants during wetland restoration: The role of disturbance, plant strategies, and environmental filters

This dissertation examines the ecological impact and management of invasive plant species during wetland restoration with a focus on three important drivers of plant community change in wetland ecosystems: disturbance, plant strategies, and environmental filters. In these experiments, the primary species of interest are Typha domingensis, Ligustrum sinense, Arundinaria gigantea, and Microstegium vimineum.;The objective of the first phase of the research was to investigate a unique Typha removal method that is used in one of the most dynamic and ecologically important wetlands in Central America (Palo Verde Marsh, Palo Verde National Park, Costa Rica). Palo Verde Marsh has historically provided important habitat for very large populations of migratory birds. However, a cattail (T. domingensis) expansion in the 1980s greatly altered the plant community and reduced avian habitat. Since then, Typha has been managed using fangueo. During fangueo, Typha is crushed and locally removed by a tractor with metal paddle wheels. The fangueo process is an effective method for restricting Typha expansion and increasing plant and avian diversity. I present a model that illustrates the impact of Typha management and seasonal flooding on the plant and avian community. The technique might be adopted or modified for the restoration and management of Typha and other invasive emergent plants in other wetlands.;The second objective of this research was to better quantify the impact of the distinct and extreme anaerobic/aerobic annual cycle on the plant community in Palo Verde Marsh. Since the impact of seasonal flooding on the plant community in seasonal wetlands is often most evident after disturbance, I created gaps in the wetland vegetation via the mechanical removal of emergent vegetation and then measured plant community change using surveys of the wet and dry season standing vegetation, the seed bank, and in situ seedling recruitment. As expected, seasonal flooding acted as an environmental filter and resulted in distinct dry and wet season assemblages. The dominant plant life forms present after vegetation removal differed between seasons with emergents dominating during the dry season and floating-rooted, free-floating, and submerged species more dominant during the wet season. I identified common species that are characteristic of both seasonal assemblages and used indicator species analyses to identify species that are only likely to be found during the wet season. I also characterized the seed bank at this site; like most seasonal wetlands, plant species' resilience in this wetland were dependent upon a large and diverse seed bank which allowed many species to revegetate after disturbance and the extreme wet/dry conditions which acted like environmental filters.;Ligustrum sinense (Chinese privet) is a very common invasive non-native shrub in the region. Arundinaria gigantea (giant cane) is a native bamboo species that used to be very abundant in riparian and wetland ecosystems in the region. The objectives of this phase of the research were to: (1) measure the plant community response to removal of mature L. sinense individuals; and (2) quantify planted A. gigantea clonal expansion in the presence of other plants, particularly common non-native invasive species. Due to its potential for rapid growth and expansion, it was hypothesized that A. gigantea would be able to compete with common non-native species and reduce non-native invasibility.;Our results emphasize several general conclusions that are applicable to other restoration efforts in other ecosystems with other plant species. First, during ecological restoration, invasive non-native plant removal alone will typically not restore native plant communities. Non-native invasive plant populations are typically very resilient to removal. Hence, long-term reductions in non-native invasibility will often require additional management efforts. For example, in the tropics my research showed the effectiveness of Fangueo for reducing Typha monocultures and increasing native plant and bird diversity. Another approach for improving ecosystems functions and reducing non-native invasibility after invasive plant removal is to carefully select and plant native species with competitive-dominant traits that will be able to compete with invading non-native species and resist invasion. Although this seemingly simple approach is often used by restoration practitioners, the results are rarely monitored and surprisingly few studies are designed to explicitly identify and investigate the performance of these important native competitive-dominant species. (Abstract shortened by UMI.)...