Managing Wetlands: Greentree Reservoirs (Flooded Live Timber)

Several million acres of bottomland hardwood timber once occurred in Missouri and throughout the lower Mississippi River valley. Today only a fraction of this unique wetland habitat remains. Recent studies have shown that the availability of flooded bottomland hardwood timber from late fall through early spring is critical to the breeding success of the mallard duck. Other studies have shown that many other species of wildlife also depend on this important wetland habitat.

Image Right: The availability of flooded bottomland hardwood timber from late fall to early spring is critical to the breeding success of the mallard duck. Many other species also depend on this important wetland habitat.

• Historically, greentree reservoirs (leveed bottomland timber that is artificially flooded) were developed to attract waterfowl during the fall and winter hunting season. Studies have shown that flooding these units the same time and depths year after year resulted in a reduction in acorn production and tree vigor, as well as causing timber mortality. Today, managers realize that long-term productivity and survival of the forest should be their management priority. To ensure that greentree reservoir habitat is available for generations to come, owners and managers should implement the following techniques:
• Vary flooding and dewatering dates. Try to emulate natural water regimes. Timber should not be artificially flooded before leaves begin to turn color in the fall, and timber must be drained before new leaves appear in the spring. Vary the dates of flooding in the fall up to a month and dewatering in the spring by up to three months. Vary flooding dates from year to year over a several year period. Flood slowly to provide optimum habitat conditions over an extended time period. Leave the unit unflooded one out of every six to eight years.
• Vary flooding depths. Flood at different depths from year to year and even within the same fall-winter period. Remember the preferred feeding depths of many ducks is less than six inches. Partial drawdowns that produce "puddling" of water tends to concentrate invertebrates that live in the leaf litter and provide an important food source.
• Dewater slowly. Nutrients associated with leaf litter decomposition that promote invertebrates and good timber vigor usually peak in early spring. A rapid dewatering of a greentree unit flushes away these nutrients. Always remove water that has been in the unit during the fall and winter slowly (one inch water level per day or less).
• Remove flood waters without delay. Flood water that inundates the wetland unit during the growing season should be removed as quickly as possible. Flooding during the growing season can cause stress and, ultimately, tree mortality if not removed within a few days. Constant monitoring of water control structures is necessary to make sure that flood waters are being drained during the timber's growing season.
• Practice good timber management. Acorn production, regeneration and reforestation all depend on a good forest management plan. Consult your local district forester to help with timber management.

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