Coastal Forests Face Rising Sea Levels, Increased Salinity

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The Albemarle-Pamlico Peninsula in North Carolina is projected to lose about half of its land area to open water with a three-foot rise in sea level. Photo courtesy of NC Wetlands.

Ghost forests aren’t some spooky legend. They’re patches of dead and dying trees that haunt the coastlines of North Carolina, South Carolina, and Virginia where sea levels are rising and land is sinking.

USDA Forest Service and Natural Resources Conservation Service scientists are working with partners across the coastal plain to understand where these watery graveyards are located and how land managers can sustain the productivity of their remaining coastal forests.

In October, the USDA Southeast Regional Climate Hub (SERCH) hosted an Experts Salinity Workshop at the Wayne County Extension Center in NC. The group of 40 experts in climate, forest, and agronomy from different USDA and state agencies, universities, and non-governmental organizations shared information about the state of saltwater intrusion science.

Nancy Gibson, a SERCH research scientist, provided an overview of salinity: its causes, impacts, and management options. She discussed natural causes of salinity, like storms and tides, and human causes, like the dense network of ditches and canals installed to drain wetlands for plantation forestry and farming.

“Salinization is expected to increase as sea levels continue to rise. Rising sea levels will inundate lands, increase tide and storm surge levels, and push salt water farther inland through ditches and tidal creeks,” says Gibson.

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SERCH connects landowners, extension specialists, and other stakeholders with tools and resources for adapting to climate change and extreme weather events. Photo by Jennifer Moore Myers, USFS.

Using a long-term dataset on tree response to salinity, William Conner and his group at the Baruch Institute of Coastal Ecology and Forest Science at Clemson University have identified a tipping point beyond which seedlings can’t survive. Mature trees are more tolerant, but without new recruits, ghost forests are created.

Coastal areas also tend to lose land to real estate development – giving trees very little area to retreat inland, away from the rising seas.

Ghost forests are at the “leading edge of climate change,” according to Emily Bernhardt, a professor at Duke University. She has studied how gradual salinization due to sea level rise has been exacerbated by episodic saltwater intrusion. Nuisance flooding is increasingly common in low-lying coastal areas, and the hyper-connected network of ditches and canals in these areas moves saltwater farther inland. Bernhardt’s biogeochemistry lab is also investigating ghost forest recovery – places where once inundated forests manage to survive.

Several climate factors are exacerbating the problem of soil salinization: greater periods of drought, more frequent and intense rainfall events, more frequent flooding from hurricanes and storm surges, and rising groundwater tables with sea level rise.

What can coastal landowners do to maintain their productive forest and agricultural lands? The workshop offered a glimpse of optimism: adaptive management such as developing and planting salt-tolerant crops or trees, applying for wetland conservation easements, and installing saltwater management controls such as ditch plugs, stacked culverts, or duckbill check valves.

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Saline agriculture and saltwater management controls can help keep forest and agricultural land healthy. “It’s not all doom and gloom,” says Miller. “There are options to reduce impacts to forest productivity and prevent farm loss.” Photo by Aileen Devlin, Virginia Sea Grant.

Chris Miller, an NRCS project liaison with both the Southeast and Northeast Climate Hubs, talked about the upper limits of salt tolerance in coastal plants. His team has established pilot plots to measure the success of different species under varying levels of salinity. Some may have inherent tolerance, while others may have the potential through genetic improvement.

SERCH is now summarizing the workshop information and will share it, along with resources for managing forests and croplands — including a salinity index for coastal surface waters in development by USGS and NOAA’s Carolinas Integrated Sciences & Assessments in South Carolina.

SERCH is also developing a regional map of saline soils. This project expands the current map of Hyde County, NC to cover the entire Southeast and include projected changes for the next 20 to 40 years.

“Our next project is a series of workshops for land managers and local stakeholders in the Carolinas and Virginia. We’re planning three opportunities in early 2020. We’ll share what the experts know and listen for saltwater impacts that you can’t find in papers,” says Steve McNulty, SERCH director and research ecologist.

“We hope to identify some practical gaps in our understanding, so we don’t look back and say, ‘I wish we’d known more about this.’ Firsthand knowledge from forest landowners and farmers is critical to this synthesis process.”

Learn more about saltwater intrusion and coastal forests.

For more information, email SERCH Director Steve McNulty at steve.mcnulty@usda.gov.

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