Wetland State-and-Transition Model Project: Annual Report - 2015

Semi-permanently flooded wetland habitats throughout the Intermountain West and western Prairie Pothole regions provide important resources for migrating and breeding migratory birds and other wetland-dependent wildlife. Significant continental-scale loss and degredation of wetlands led to establishment of some of the regions’ largest wetland complexes as National Wildlife Refuges (NWRs) (e.g., Benton Lake, Malheur, and Red Rock Lakes NWRs) and state Wildlife Management Areas (WMA) (e.g., Farmington Bay, Freezeout Lake, and Market Lake WMAs). Wetland management actions often mimic natural disturbance processes in order to maintain ecological function. Objectives for semi-permanently flooded wetland habitats within these regions typically focus on one of the two following approaches to management: 1) managing for wetland function to provide a desired plant community or 2) managing to provide habitat for a specified population size and/or life-history requirement(s) of focal wildlife species. For example, sago pondweed (Stuckenia pectinata), a pioneering wetland plant species, is more nutritious and often more preferred by migratory birds than species more tolerant of anoxic conditions such as watermilfoil (Myriophyllum sibiricum). Hence, management objectives for semi-permanently flooded wetlands often include maintaining a relatively high abundance of sago pondweed for the benefit of migratory birds. The primary disturbance process of management interest in semi-permanently flooded wetland habitats is the dynamic wet/dry hydrological cycle, which is a key driver of wetland productivity and vegetation community structure. Water level changes (either managed or natural) are perterbations that influence nutrient turnover rates, vegetation, aquatic invertebrates, and resource availability for wetland-dependent wildlife. Wetland systems can respond to perturbations in a non-linear fashion with multiple states and phases possible. The frequency, timing, and duration of drawdowns (natural or managed) are important factors in determining which vegetation community phases are expressed within a semi-permanently flooded wetland area. The ability to predict the biological outcome of water level changes varies depending on the knowledge of the wetland system being managed.