Short-Term Effects of Burning and Disking on Songbird Use of Floodplain Conservation Easements

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ABSTRACT.-

Extensive conversion of Midwestern riparian areas for agricultural production has had many consequences including reduced habitat for nesting birds. However, more than 120,000 ha of riparian habitat have been restored in this region through USDA conservation programs. In 2001 and 2002, we assessed songbird responses to burning and disking for management of conservation easements in east-central Iowa. We randomly assigned herbaceous riparian fields to burning and disking treatments and collected data on density and species richness of songbirds in these habitats. Total density of grassland and wetland species and red-winged blackbirds (Agelaius phoeniceus) were reduced by burning in the first and second breeding seasons after burning; common yellowthroat (Geothlypis trichas) density decreased with burning only in the first season. Disking led to increased density of grassland and wetland birds and greater overall avian conservation value on treated relative to untreated fields in the year after treatment. Changes associated with burning and disking treatments were likely related to changes in both vegetation structure and abundance of arthropod food resources. Despite decreased bird densities with burning, fire is a necessary management tool to control woody vegetation. Overall, both burning and disking appear to be effective management practices for maintaining herbaceous riparian habitats for grassland birds.

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INTRODUCTION

Since European settlement, the Midwestern United States has undergone major landcover changes. Prairies and wetlands have been reduced to a fraction of their former extent and rowcrop agriculture has become the dominant land use in many areas (Dahl, 1990; Samson and Knopf, 1994). In Iowa, this conversion of presettlement landscapes to agriculture has resulted in the loss of >99% of native prairie and >95% of wetlands (Bishop, 1981; Smith, 1998). As interfaces between terrestrial and aquatic ecosystems, riparian areas are important landscape components that, like other natural communities, have been greatly altered. The loss of native floodplain functions, including flood-water storage, nutrient and sediment retention, and wildlife habitat, has been more widespread in the Midwest than in any other region of the United States (Brinson et al, 1981; National Research Council, 2002).

Historically, the structure and composition of Midwestern riparian plant communities were shaped by fine-scale elevation differences and the timing, duration and extent of disturbances such as flooding and fire (Brinson et al, 1981; Gregory et al, 1991; Nelson et al, 1998). Although some riparian areas were forested before European settlement, many of these areas were dominated by extensive grasslands and herbaceous wetlands (Weaver, 1968; Nelson et al, 1998; Benson et al, 2006). This diversity of habitat types and hydrologie conditions historically made riparian areas important for a diversity of plant and animal species (Fredrickson and Reid, 1986; Iowa Department of Agriculture and Land Stewardship, 1999).

In the past two decades, the implementation of Farm Bill programs such as the Conservation Reserve Program (CRP) and Wetlands Reserve Program (WRP) has led to restoration of millions of hectares of grasslands and wetlands. Authorized in 1990, WRP is a voluntan' program in which landowners are compensated for taking their land out of agricultural production and restoring natural vegetation (Gray, 2005). Combined with emergency flood-mitigation programs such as the Emergency Wetlands Reserve Program (EW7RP), CRP and WRP have restored thousands of hectares of riparian habitat throughout the Midwest. These programs have a variety of goals, including providing habitat for wildlife populations, especially migratory birds (Heard et al, 2000). Through these programs, restoration of riparian grasslands and wetlands may benefit many bird species, including those that have experienced widespread and consistent population declines (Peterjohn and Sauer, 1999; Benson et al, 2006). …