Restoring diversity after cattail expansion: disturbance, resilience, and seasonality in a tropical dry wetland.

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2011-04

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Abstract

As the human footprint expands, ecologists and resource managers are increasingly challenged to explain and manage abrupt ecosystem transformations (i.e., regime shifts). In this study, we investigated the role of a mechanical disturbance that has been used to restore and maintain local wetland diversity after a monotypic regime shift in northwestern Costa Rica [specifically, an abrupt landscape-scale cattail (Typha) expansion]. The study was conducted in Palo Verde Marsh (Palo Verde National Park; a RAMSAR Wetland of International Importance), a seasonally flooded freshwater wetland that has historically provided habitat for large populations of wading birds and waterfowl. A cattail (T. domingensis) expansion in the 1980s greatly altered the plant community and reduced avian habitat. Since then, Typha has been managed using a form of mechanical disturbance called fangueo (a Spanish word, pronounced "fahn-gay-yo" in English). We applied a Typha removal treatment at three levels (control, fangueo, and fangueo with fencing to exclude cattle grazing). Fangueo resulted in a large reduction in Typha dominance (i.e., decreased aboveground biomass, ramet density, and ramet height) and an increase in habitat heterogeneity. As in many ecosystems that have been defined by multiple and frequent disturbances, a large portion of the plant community regenerated after disturbance (via propagule banking) and fangueo resulted in a more diverse plant community that was strongly dictated by seasonal processes (i.e., distinct wet- and dry-season assemblages). Importantly, the mechanical disturbance had no apparent short-term impact on any of the soil properties we measured (including bulk density). Interestingly, low soil and foliar N:P values indicate that Palo Verde Marsh and other wetlands in the region may be nitrogen limited. Our results quantify how, in a cultural landscape where the historical disturbance regime has been altered and diversity has declined, a mechanical disturbance in combination with seasonal drought and flooding has been used to locally restrict a clonal monodominant plant expansion, create habitat heterogeneity, and maintain plant diversity.

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Richardson

Curtis J. Richardson

Research Professor of Resource Ecology in the Division of Environmental Science and Policy

Curtis J. Richardson is Professor of Resource Ecology and founding Director of the Duke University Wetland Center in the Nicholas School of the Environment. Dr. Richardson earned his degrees from the State University of New York and the University of Tennessee.

His research interests in applied ecology focus on long-term ecosystem response to large-scale perturbations such as climate change, toxic materials, trace metals, flooding, or nutrient additions. He has specific interests in phosphorus nutrient dynamics in wetlands and the effects of environmental stress on plant communities and ecosystem functions and services. The objectives of his research are to utilize ecological principles to develop new approaches to environmental problem solving. The goal of his research is to provide predictive models and approaches to aid in the management of ecosystems.

Recent research activities: 1) wetland restoration of plant communities and its effects on regional water quality and nutrient biogeochemical cycles, 2) the development of ecosystem metrics as indices of wetland restoration success, 3) the effects of nanomaterial on wetland and stream ecosystem processes, 4) the development of ecological thresholds along environmental gradients, 5) wetland development trends and restoration in coastal southeastern United States, 6) the development of an outdoor wetland and stream research and teaching laboratory on Duke Forest, 7) differential nutrient limitation (DNL) as a mechanism to overcome N or P limitations across trophic levels in wetland ecosystems, and 8) carbon sequestration in coastal North Carolina pocosins.

Richardson oversees the main analytical lab in NSOE, which is open to students and faculty. Dr. Richardson has been listed in Who's Who in Science™ annually since 1989 and was elected President of the Society of Wetland Scientists in 1987-88. He has served on many editorial review committees for peer-reviewed scientific journals, and he is a past Chair of the Nicholas School Division of Environmental Sciences and Policy. Dr. Richardson is a Fellow of the American Association for the Advancement of Science, the Society of Wetland Scientists, and the Soil Science Society of America.


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