A green tree reservoir (GTR) consists of

bottomland hardwood forest The bottomland hardwood forest is a type of deciduous and evergreen hardwood forest found in broad lowland floodplains along large rivers and lakes in the United States and elsewhere. They are occasionally flooded, which builds up the alluvial soi ...

land which is shallowly flooded in the fall and winter. Prior to modern industrialization and commercial farming, the Southeastern United States was home to more than 10 million hectares of bottomland hardwood forest. Today, there is only about 2.8 million hectares remaining (King et al. 2008). Not only are southeastern hardwood forests disappearing, but there has been a huge effort to control water flow so that natural forest flooding is less frequent. Bottomland hardwood forest is an important wetland habitat for many species of waterfowl, as well as other animals. In order to support migrating waterfowl, both private land managers and public agencies implement green tree reservoirs. In a GTR, a forest stand is flooded to create a seasonal wetland. These seasonal wetlands provide habitat and food for

waterfowl Anseriformes is an order of birds also known as waterfowl that comprises about 180 living species of birds in three families: Anhimidae (three species of screamers), Anseranatidae (the magpie goose), and Anatidae, the largest family, which in ...

amphibians Amphibians are four-limbed and ectothermic vertebrates of the class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terrestrial, fossorial, arbore ...

, and many other species.

Management

The water level on green tree reservoirs are manipulated by flooding and “draw down,” a process in which water is drained off of the reservoir. There are many methods for flooding a forest stand (Fredrickson and Batema 1992), many of which use levees or dykes. Water is either diverted from a natural source or pumped onto the landscape. This usually occurs in early winter, when trees are dormant and less likely to be damaged by standing water. The water should be drawn down before the tree dormancy stage has ended. This dormant season coincides with waterfowl migration, providing habitat for migrating birds. In most cases, GTRs are flooded to a depth of 2-10 inches. Waterfowl in the order

Anatinae The Anatinae are a subfamily of the family Anatidae (swans, geese and ducks). Its surviving members are the dabbling ducks, which feed mainly at the surface rather than by diving. The other members of the Anatinae are the extinct moa-nalo, a youn ...

are dabbling ducks that require only a shallow water depth. Diving ducks are less common on the

Mississippi Flyway The Mississippi Flyway is a bird migration route that generally follows the Mississippi, Missouri, and Lower Ohio Rivers in the United States across the western Great Lakes to the Mackenzie River and Hudson Bay in Canada. The main endpoints of t ...

, but they also can utilize a water depth of only 10 inches. The water depth in a GTR will likely not be uniform. Various water depths allow for different types of food to be available at one time (Fredrickson and Reid 1988). Every species of animal that uses a GTR has slightly different food and habitat needs. Knowing the life history of the target species is critical to proper manipulation of a GTR. There are plant and tree species specifically beneficial to waterfowl (discussed below), and the abundance of these species and forest composition can be managed by adjusting flood and draw down on the reservoir (Young et al. 1995). Bottomland hardwood forests can also be effectively manipulated by removing timber; in some cases it is required to maintain viable forest stands (Kellison and Young 1997). Older research reflects the view that standing water in GTRs permanently damages trees and acorn production. (Young et al. 1995, Wigley and Filer 1989). However, more current research (King et al. 2006) shows that when managed properly, green tree reservoirs can be very productive. Many researchers have found that production in GTRs is highest when managers try to emulate natural hardwood wetlands (Fredrickson and Reid 1988, King and Allen 1996). In 1985, 95% of GTRs were flooded annually and for longer than the dormancy season of the forest (Wigley and Filer 1989). Many plant species are adapted to a higher water tolerance; working with those plants rather than trying to force a dry-adapted plant to function in a wetland has increased GTR success. For example,

pin oak ''Quercus palustris'', the pin oak or swamp Spanish oak, is a tree in the red oak section (''Quercus'' sect. ''Lobatae'') of the genus ''Quercus''. Pin oak is one of the most commonly used landscaping oaks in its native range due to its ease of ...

s are a wetland oak and have small acorns suitable for waterfowl. In one study, researchers found that pin oak acorns even suffered less insect infestation (and therefore produced more usable food items for waterfowl) in flooded areas than in non-flooded forests (McQuilkin and Musbach 1977). Encouraging wetland plants suited for seasonally flooded areas supports the natural wetland model and results in better food sources. In another example, it was found that fall flooding decreases grain availability for spring-migrating waterfowl (Greer et al. 2007). Now that more research has emerged detailing the natural life history of wetland plants and trees, GTR managers are better prepared to manipulate the resource.

Waterfowl production

The main use of GTRs is to increase production of waterfowl. This is especially true in the southeastern United States, where the Mississippi Flyway encourages duck hunting. Waterfowl that use the

include

American black duck The American black duck (''Anas rubripes'') is a large dabbling duck in the family Anatidae. It was described by William Brewster in 1902. It is the heaviest species in the genus ''Anas'', weighing on average and measuring in length with an ...

(''Anas rupribes''),

blue-winged teal The blue-winged teal (''Spatula discors'') is a species of bird in the duck, goose, and swan family Anatidae. One of the smaller members of the dabbling duck group, it occurs in North America, where it breeds from southern Alaska to Nova Scotia ...

(''Anas discors''),

green-winged teal The green-winged teal (''Anas carolinensis'') is a common and widespread duck that breeds in the northern areas of North America except on the Aleutian Islands. It was considered Conspecificity, conspecific with the Eurasian teal (''A. crecca'') ...

(''Anas crecca''),

gadwall The gadwall (''Mareca strepera'') is a common and widespread dabbling duck in the family Anatidae. Taxonomy The gadwall was first described by Carl Linnaeus in his landmark 1758 10th edition of ''Systema Naturae''. DNA studies have shown that ...

(''Anas strepera''),

northern shoveler The northern shoveler (; ''Spatula clypeata''), known simply in Britain as the shoveler, is a common and widespread duck. It breeds in northern areas of Europe and across the Palearctic and across most of North America, wintering in southern Euro ...

(''Anas clypeata''),

northern pintail The pintail or northern pintail (''Anas acuta'') is a duck species with wide geographic distribution that breeds in the northern areas of Europe and across the Palearctic and North America. It is migratory and winters south of its breeding ra ...

(''Anas acuta''),

mallard The mallard () or wild duck (''Anas platyrhynchos'') is a dabbling duck that breeds throughout the temperate and subtropical Americas, Eurasia, and North Africa, and has been introduced to New Zealand, Australia, Peru, Brazil, Uruguay, Arge ...

(''Anas platyrhynchos''),

wood duck The wood duck or Carolina duck (''Aix sponsa'') is a species of perching duck found in North America. The drake wood duck is one of the most colorful North American waterfowl. Description The wood duck is a medium-sized perching duck. A typi ...

(''Aix sponsa''), and many others. Migrating waterfowl have high energy needs and require stopover points on their migration route (Martin and Finch 1995). With much of the bottomland hardwood forest in the southeast US destroyed, GTRs provide food and habitat for waterfowl during migration. During a migration stopover, studies have shown that a duck’s diet may consist of 60% acorns or mast (Allen 1980). Migrating waterfowl require good sources of carbohydrates and protein. Acorns are an important food source for waterfowl, but not every acorn is an acceptable food. Acorns must be small enough for a duck to swallow comfortably. Oak species that produce small acorns includes willow oak(''

Quercus phellos ''Quercus phellos'', the willow oak, is a North American species of a deciduous tree in the red oak group of oaks. It is native to the south-central and eastern United States. Description It is a medium-sized tree growing to tall (exceptional ...

''), water oak (''

Quercus nigra ''Quercus nigra'', the water oak, is an oak in the red oak group (''Quercus'' sect. ''Lobatae''), native to the eastern and south-central United States, found in all the coastal states from New Jersey to Texas, and inland as far as Oklahoma, Kent ...

''), pin oak (''

Quercus palustris ''Quercus palustris'', the pin oak or swamp Spanish oak, is a tree in the red oak section (''Quercus'' sect. ''Lobatae'') of the genus ''Quercus''. Pin oak is one of the most commonly used landscaping oaks in its native range due to its ease of ...

''), Nutall’s oak (''

Quercus texana ''Quercus texana'', commonly known as Nuttall's oak, is a fast-growing, large deciduous oak tree. It is a tree growing up to 25 meters (83 feet) tall, with dark brown Bark (botany), bark. It has leaves with sharp pointed lobes somewhat similar ...

''), among several others. When a GTR is flooded, these acorns float to the surface; herbaceous vegetation is also available. Invertebrates common in the leaf litter “bloom” and provide protein for breeding waterfowl. According to the Waterfowl Management Handbook (Fredrickson and Reid 1988), there are three criteria for foods to be available to waterfowl. : : “Foods are accessible if: :1. Appropriate water depths are maintained during critical time periods. :2. Habitats are protected from disturbance :3. Habitats that provide protein and energy are close to one another”Fredrickson, L. H. and F. A. Reid. 1988. Waterfowl management handbook. USFWS Fish and Wildlife Leaflet 13.2.1. Washington D. C. : According to Fredrickson and Reid (1988), disturbance from any source is detrimental to waterfowl during their stopover. Proper water depths and the juxtaposition of protein and energy contribute to waterfowl success.

References

{{DEFAULTSORT:Green Tree Reservoir Forest ecology