Conservation: Renovating Greentree Reservoirs

Careful management is required to maintain the productivity of these classic waterfowl habitats
By Jody Pagan

After graduating from college I spent nine months working on a wildlife habitat mapping project. At the completion of the project, I received a certificate of merit that included a quote from the great Aldo Leopold: "The key to intelligent tinkering is to keep all the parts." Leopold's words are especially relevant to those working in wetland restoration.

In the case of the Mississippi Alluvial Valley (MAV), a crucial wintering area for mallards and many other waterfowl species, we did not save all the parts. Of the 24 million acres of seasonally flooded bottomland hardwood forest that once existed across this region, less than 5 million acres remain. In eastern Arkansas alone, more than 72 percent of this important waterfowl habitat has been cleared and drained. 

Much of the remaining bottomland hardwood forest in the MAV is found in fragmented blocks. Many of these isolated tracts have been developed into "greentree reservoirs" for waterfowl hunting. A greentree reservoir is defined as a stand of bottomland hardwood forest that is equipped with a levee system, water-control structures, and in some cases wells and pumps. Managed on both public and private land, greentree reservoirs are flooded in late fall, when oaks and other trees are dormant, to provide crucial wintering habitat for waterfowl. Duck hunters from all over the world travel to Arkansas to hunt mallards in the flooded timber, something all waterfowlers should experience at least once.  

Pioneered during the 1930s, early management of greentree reservoirs was fairly simple. Managers would flood impoundments to full pool by opening day, and then drain the impoundments the day after the close of duck season. A standard practice was to start pumping on October 1 or earlier. In the MAV, October is the driest month of the year. While early flooding was not good for the trees, it did offer much-needed habitat for mallards and other dabbling ducks. During dry years, the hunting was phenomenal in these artificially flooded forests. Over time, however, the productivity of many greentree reservoirs declined as the long-term effects of early flooding took a toll on timber health and habitat quality. 

Of particular concern to managers is the health of red oaks, which can produce bumper crops of acorns that provide food for mallards and other dabbling ducks. For decades researchers struggled to determine how to keep red oaks alive in greentree reservoirs. Studies were conducted to better understand forest health and natural flooding regimes, identify management problems, and develop corrective measures. The most notable research was led by Dr. Leigh Fredrickson of the University of Missouri. By the late 1990s, this research made clear that flooding before the first frost as well as long-duration flooding can cause a catastrophic collapse of the red oak component in greentree reservoirs. 

In 2005, I was hired by current DU President George Dunklin Jr. as a biologist and general manager of Five Oaks Wildlife Services, LLC, in Arkansas. My job was to manage the Five Oaks property, complete the renovations of several greentree reservoirs, and develop a renovation program that could be used by other private landowners with similar habitat quality issues. Dunklin had a long-term vision and a passion for habitat like nothing I'd ever experienced outside the scientific community. 

Working together, we developed the following seven-step plan to help greentree reservoir managers restore the health and productivity of their properties and provide high-quality, sustainable habitat for waterfowl and other wildlife: 

  1. Conduct an Assessment The first step is to conduct a thorough assessment of the area. This includes a timber inventory to determine the health and composition of the forest. All levees, water-control structures, ditches, borrow pits, relift pumps, and wells should be checked to identify any possible engineering concerns. The density of the forest canopy, which affects how much sunlight reaches the forest floor, and the abundance of herbaceous (non-woody) plants should also be assessed. 

  2. Develop a 100-Year Plan Managing a greentree reservoir is a long-term proposition, so we recommend that landowners develop a "100-year plan" outlining the infrastructure and water-management practices that will be required to ensure the long-term health and productivity of the timber. The natural state of the forest before levees were built and any negative impacts resulting from past management should also be determined. Most 100-year plans include timber stand improvement recommendations that will help increase the percentage of red oaks and foster the growth of other beneficial vegetation. The key point is that all greentree reservoirs are unique, and management plans should be site-specific to ensure long-term success.

  3. Correct the Plumbing Inadequate drainage is a common problem in greentree reservoirs. Consider the following questions to ensure that all the plumbing is up to the task: Do all the ditches drain completely? Do abandoned levees or spoil banks impede drainage? Do water-control structures have enough capacity to remove water quickly? Is an effective beaver-management program in place? 

  4. Increase Your Pumping Capacity if Necessary The inability to deliver enough water to flood greentree reservoirs in a timely manner is one of the main reasons managers begin pumping too early. Our experience indicates that optimal pumping time is 20 days or less. If you have the available water, install a pump with the capacity to get the job done as quickly as possible. 

  5. Manage the Forest Cutting trees can be a good thing when it comes to creating high-quality waterfowl habitat in greentree reservoirs. Managers should hire a registered professional forester specializing in bottomland hardwood management. A forester will survey and create an inventory of the timber on your property, mark timber for harvesting, and in some cases take bids from logging contractors on your behalf. Before cutting any timber, however, be sure to have a written contract specifying all aspects of the job, including the timing of the harvest, when the crew can work, the type of equipment that can be used, and the condition of the site once the harvest is complete. 

  6. Replant Red Oaks Once the red oak component is lost in an impoundment, the only way to restore those species is through reforestation. We have found that planting seedlings in three-gallon containers at a rate of 50 to 193 seedlings per acre is the best method for restoring red oaks in greentree reservoirs. However, planting red oaks is not possible on all sites. If you can't control water levels enough to ensure the long-term survival of replanted trees, don't waste your time and money. 

  7. Practice Good Water Management Floodplain forests naturally experience wet and dry periods on an annual and semiannual basis. Managers should replicate these natural wet and dry cycles to ensure the health of timber in greentree reservoirs. The timing of the waterfowl migration should also be considered when flooding greentree reservoirs. If mallards don't arrive in large numbers until the first week of December, why risk the health of your red oaks by flooding them too early? There is often a trade-off between habitat quality and the number of days that you can hunt a greentree reservoir each season. Our experience in managing greentree reservoirs indicates that habitat quality has a much greater effect on hunting success and harvest than does the number of days hunted. 


Jody Pagan is a biologist and general manager of Five Oaks Wildlife Services, LLC, in Stuttgart, Arkansas.