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Restoring Diversity after Cattail Expansion: Disturbance, Resilience, and Seasonality in a Tropical Dry Wetland.
Citation:
OSLAND, M. J., E. GONZALEZ, AND C. RICHARDSON. Restoring Diversity after Cattail Expansion: Disturbance, Resilience, and Seasonality in a Tropical Dry Wetland. ECOLOGICAL APPLICATIONS. Ecological Society of America, Ithaca, NY, 21(3):715-728, (2011).
Impact/Purpose:
In this study, we investigate the role of an unusual form of mechanical disturbance that has been used to maintain local wetland diversity after a monotypic regime shift in northwestern Costa Rica [specifically, an abrupt landscape-scale cattail (Typha) expansion]. Our investigation examines the impact of repeated disturbance, resilience, and seasonality on the plant and avian community in an ecosystem where high diversity has historically been maintained by multiple and frequent disturbances.
Description:
As the human footprint expands, ecologists and resource managers are increasingly challenged to explain and/or manage abrupt ecosystem transformations (i.e., regime shifts) that have produced novel ecosystems. In this study, we investigate 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). During fangueo, Typha is crushed and locally removed by a tractor with metal paddle wheels. 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 (decreased aboveground biomass, ramet density, and ramet height), an increase in habitat heterogeneity, and a 98 and 5-fold increase in avian density and richness, respectively. As in many seasonally flooded wetlands, a large portion of the plant community is resilient to disturbance (via propagule banking) and fangueo resulted in a more diverse plant community that was strongly dictated by seasonal processes (distinct wet/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 and maintain wetland diversity.