Bottomland Hardwoods of the Mid-Atlantic

Update on FIA status and trends

A new U.S. Forest Service report characterizes the status and trends of bottomland hardwood forests across the mid-Atlantic region of North Carolina and Virginia. These forests are located in floodplains, bogs, swamps, and other lowland areas. SRS scientists Anita Rose and Steve Meadows summarized Forest Inventory and Analysis (FIA) data from 2002 to 2014 for the Coastal Plain and Piedmont areas of the two states.

Bottomland hardwoods make up about 13 percent of the mid-Atlantic region’s 22.1 million acres of forest land, with the dominant forest-type group of loblolly and shortleaf pines covering another 37 percent. The most abundant bottomland hardwood forest type was sweetbay / swamp tupelo / red maple, about 45 percent by area.

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Invasive species and forest type conversion pose threats to the long-term sustainability of bottomland hardwoods. Photo courtesy of U.S. Fish and Wildlife Service.

The total volume–an estimate of tree size made from height and diameter measurements–of bottomland hardwood trees remained steady over the survey period, with some species like white oak increasing and other species like red oak decreasing.

“We don’t have sufficient data to say definitively what’s behind the decrease in red oak volume,” said Rose, at the time of publication a research ecologist with the SRS Forest Inventory & Analysis unit. “Possible explanations include increased harvesting in recent years, decreased growth due to poor or no management, or some combination of both.”

Other important trends and findings:

  • Forest land area in the region held steady at around 22 million acres over the survey period.
  • Top bottomland hardwood forest species, by number of trees, were red maple, sweetgum, and swamp tupelo.
  • After an increase in mortality from the mid-1980s to the mid-2000s, net growth in the region’s bottomland hardwood forests recovered to 93.1 cubic feet per acre per year by the end of the survey period.
  • Removals in bottomland hardwood forests averaged between 37.6 and 55.3 cubic feet per acre per year, while removals in the region overall declined from 74.5 cubic feet per acre per year in 2007 to 53.5 in 2014, due, at least in part, to the economic downturn of 2007-2008.

The scientists examined several of these measurements to assess the sustainability of the region’s bottomland hardwoods. The ratio between growth and removals is useful to compare growth trends with harvest and mortality levels. This ratio stayed above 1:1—a threshold for sustainable practices—for bottomland hardwoods in the region.

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Baldcypress trees, though technically not hardwoods, are important members of lowland forest communities. Photo by bobistraveling, courtesy of Wikimedia Commons.

Another indicator is the amount of forest land area in different age and size classes. Mid-Atlantic bottomland hardwood forests were equally spread across most stand-age classes, with fewer acres in the greater than 80 years class likely due to standard forest management practices such as harvesting and regeneration.

Bottomland hardwood forest area in large-diameter stands increased (to 59 percent of the total) over the survey period, while the area of small-diameter stands decreased, suggesting that the forest resource is maturing.

This is particularly true for the oak / gum / cypress forest-type group, which includes the sweetbay / swamp tupelo / red maple forest type. Managed regeneration in stands with large-diameter cypress and tupelo can prevent wetland shrubs like buttonbush or invasive privet from replacing these tree species.

“The data seem to indicate a shortage of cypress-tupelo forest land in small- and medium-diameter size classes,” Rose surmised. “If these trends continue and the distribution of stand-size classes across the landscape becomes more unbalanced, the sustainability of bottomland hardwood forest resources in the mid-Atlantic region may be threatened.”

Read the full text of the report.

For more information, email Anita Rose at anitarose@fs.fed.us.

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