Nature Lab

Greentree Reservoir Research

Study seeks to improve flooded timber management for winter waterfowl habitat

Every winter, the floodplains of the lower Mississippi Valley provide flooded forest habitat for waterfowl, migratory birds, and other wildlife. Historically, this habitat flooded naturally. But as more acres were progressively drained for agriculture, natural resource managers began creating what are known as greentree reservoirs (GTRs), flooding portions of the bottomland forest each fall via levees and water control structures. Research shows that GTR flooding benefits both the desired trees and wildlife. Over time, however, that begins to change.

At issue are pin oaks and other red oak species whose acorns provide winter food for wood ducks and mallards in these areas. Managers must create conditions so these sun-loving oaks can regenerate under the additional effects of annual shallow flooding. Dormant trees can generally withstand flooding, so GTRs are flooded after trees lose their leaves in autumn and drained in spring before leaves start growing. At first, this system seems to support the oaks, but after about 10 years, the oak trees produce fewer acorns; fewer oak seedlings survive; waterfowl use declines; and ash, elm, and maple species begin to dominate the forests.

“We’ve been flooding and draining at very specific times of the year, and we’re starting to understand that we need more information about dormancy,” explains MDC Research Forester Brad Graham. “We need to understand what’s going on below ground.”

In 2019, MDC and partners began a three-part study to find this out. They are investigating: 1) air and soil temperatures and soil moisture in GTRs throughout the year, 2) how these temperatures and floodings affect oak seedlings and root growth, and 3) how the flooding regime has affected the mature oaks over time.

The goal is to learn which environmental conditions signal the optimal time(s) for flooding. As results come in, Graham says, we’re “developing the necessary information to fine-tune this system, to make sure we are doing our best to maintain those target oak species in the overstory.”

At a Glance

Greentree reservoirs are flooded each fall to provide habitat for migratory birds, waterfowl, and other animals. This practice began in Arkansas in the 1930s and spread to surrounding states as natural flooding waned due to agriculture and other land use changes. MDC and partners are researching how to fine-tune the flooding regime so the desired oak species will continue to regenerate and thrive in these areas.

Partners

Arkansas Game and Fish Commission, U.S. Forest Service, U.S. Fish and Wildlife Service, University of Missouri, University of Arkansas

Learn more at short.mdc.mo.gov/4aE