Restoring diversity after cattail expansion: disturbance, resilience, and seasonality in a tropical dry wetland.
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.
Type
Journal articleSubject
BiodiversityBiomass
Costa Rica
Environmental Monitoring
Population Density
Seasons
Seeds
Soil
Tropical Climate
Typhaceae
Wetlands
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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 phosphor

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