Research Product

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