Green-Tree Reservoir management practices within the U.S. Fish and Wildlife Service National Wildlife Refuge System

Science Center Objects

Green-Tree Reservoirs are used as a management tool by National Wildlife Refuges throughout the Southeast United States, but data suggests that forest productivity has declined in these areas. USGS investigates the effects of climate and flooding on tree growth and mortality to assist refuge managers adapt management strategies. 

Map of Green-Tree Reservoirs (GTRs)

Map of Green-Tree Reservoirs (GTRs)

The Science Issue and Relevance: Green-Tree Reservoirs (GTRs) are bottomland hardwood forests that are artificially flooded during late fall and winter to provide waterfowl habitat. GTRs are used extensively as a management tool by National Wildlife Refuges (NWRs) throughout the Mississippi Alluvial Valley and Southeastern U.S. and now exist in more than 20 states. This geographic area spans a wide range of climate variability, including temperature and precipitation gradients. GTRs were initially conceived as an expansion of waterfowl habitat by artificially flooding and impounding bottomland hardwood tracts during the fall and winter months when the trees were considered to be dormant. However, data gathered by WARC scientists have shown that there has been a steady decline in GTR forest productivity at Felsenthal National Wildlife Refuge in southern Arkansas over the last 25 years. Little is known about the actual causes or tipping points related to progressive GTR forest decline or the interactive effects of flooding and winter temperature minimum or summer drought on wetland forest productivity within GTRs over the geographic range of this habitat management strategy.  

Methodologies for Addressing the Issue: Forest plots have been installed within Green-Tree Reservoirs in Arkansas at Felsenthal NWR (1985) and White River NWR (2012) to investigate the interactive effects of managed flood regimes and climate (winter temperatures and summer drought cycles) on tree growth, vigor, and mortality. Cores were extracted from selected dominant and co-dominant trees within the plots for tree-ring analysis of long-term growth rates. Water-level gages were installed to record seasonal timing, duration, and depth of flooding of the GTRs. Detailed analyses of the effects of climate and flooding regime on tree growth and mortality aid refuge managers to adapt management strategies of GTRs to local climate conditions and reduce adverse effects to the wetland forest ecosystem.

Future Steps: During 2015-16, GTR forest plots will be installed at Overflow NWR in Arkansas and Atchafalaya NWR in Louisiana. A reconnaissance trip was made in 2015 to Mingo NWR in Missouri to explore the possibility of installing GTR plots there. This would expand the refuge GTR network to include refuges in warmer and colder climates. We hypothesize that the climate gradient will correlate with forest plot characteristics and shed light on the potential effects of climate change on species growth and productivity.

Vigor class changes at Felsenthal NWR

Vigor class changes at Felsenthal NWR

Related Project(s) and Product(s):

  • Keelsnd, B. D., R. O. Draugelis-Dale, and J. W. McCoy. 2010. Tree growth and mortality during 20 years of managing a green-tree reservoir in Arkansas, USA. Wetlands 30:405-416.