Decline and Recovery of Small Mammals After Flooding: Implications for Pest Management and Floodplain Community Dynamics

Floodplains often are managed both for agriculture and as habitat for native species. On the Sacramento River, farmers have expressed concern that natural areas may harbour small mammals in greater abundance than occurs on farms, which could make them sources of pests to adjoining farmlands. Concern over this has generated some opposition to riparian restoration. To better understand the issue, we studied small mammals at agricultural sites, young and older riparian restoration sites and remnant natural areas through live trapping and visual surveys over three successive years. Significant flooding occurred during the second winter of the study. We found that young riparian restoration sites (3–4 years since planting) did not harbour agricultural pests (e.g. California ground squirrel, Botta's pocket gopher) in greater abundance than agricultural sites, with the exception of California voles. Although voles were common at young sites, they declined dramatically as the sites matured, and neither 12‐ to 15‐year‐old sites nor remnant riparian habitats had higher abundances of any small mammal pest species than agricultural sites. All species except the arboreal western gray squirrel experienced significant population declines following the flood and remained at depressed levels for at least a full year thereafter. Native species were not less susceptible to flooding than exotic species. California vole was the first species to recover. Our study suggests that frequent winter flooding may be desirable from an agricultural pest management perspective. It illustrates a valuable ecosystem service, small mammal pest control, which is provided by flooding, an important natural disturbance process.