Photo by Seth Maddox
MONTGOMERY-Bottomland hardwood forests are found along many water bodies in Alabama and throughout the Southeast. These areas, primarily composed of hardwood trees, provide year-round food, cover and nesting areas for a variety of game and nongame wildlife species. Many of these areas experience periods of natural flooding that provide excellent foraging opportunities for waterfowl. During times of flooding, food that is not normally available, such as acorns and many organisms that live in the soil, can be easily consumed. These newly available food sources make the areas a great attractant for waterfowl. Such habitats should be protected and extreme caution used to protect the hydrology in these areas. However, on sites where the hydrology does not allow flooding to occur naturally, levees can be created to flood the forested areas. This creates areas referred to as “green-tree reservoirs.”
Green-tree reservoirs were first developed during the 1930s in Arkansas. They can be used to provide a controllable habitat to attract waterfowl during the fall months. The reservoirs are constructed using levees to surround an area primarily composed of hard mast-producing bottomland tree species such as overcup, willow, Nuttall, water, cherrybark and Shumard oaks. A water control device such as a flash-board riser, screw-gate or drop log, is used to regulate water levels within the reservoir. The levee and water control structure allow areas to be flooded to a maximum average depth of 18 inches.
Green-tree reservoirs should be located on sites with little or no slope and soils with very low permeability, such as clay. The site also needs to have an adequate supply of water. Lakes, rivers, wells and rainfall all offer potential water sources. Rainfall offers the most economical way to flood a green-tree reservoir and allows for the most natural flooding pattern. However, rainfall is the least reliable source of water.
Another factor to consider is the composition of the area being flooded. The area must have a strong oak component to create the desirable effects. A lot of thought and planning should go into the construction of a green-tree reservoir before one is constructed.
Once the decision is made to implement this strategy and a green-tree reservoir constructed, it should be managed to maximize its potential. The reservoir should be flooded in the fall after the leaves change color and trees have gone into the dormant stage, and drained before the buds on the trees begin to swell. This allows the trees to be flooded during their dormant cycle and minimizes damage to them.
Flooding the reservoir for too many consecutive years, or flooding it when the trees are not in their dormant stage, can kill the less water-tolerant oak species and promote water-tolerant species, which are undesirable in this system. To avoid this, the reservoir should be flooded every other year, or flooded for three years in a row and then left dry for two years. Both strategies allow for flooding three out of five years. Regardless of how often the reservoir is flooded, the health and composition of the trees needs to be monitored.
Considerable time and resources can go into the construction and maintenance of a green-tree reservoir. Careful thought and planning needs to take place before implementing this technique on a property. However, a green-tree reservoir, along with the protection of natural flooding habitats, can be a very beneficial tool to enhance wildlife habitat and attract many waterfowl species.
MEDIA RELEASE/ Justin Brock, Wildlife Biologist, Alabama Division of Wildlife and Freshwater Fisheries
