Type “sea-level rise” in an internet search engine and most of the resulting images will show flooded cities. You would also find ample guidance on civic options for protecting urban infrastructure, from constructing seawalls to elevating roadways.
But a new study by Assistant Professor of Biology Keryn Gedan and researchers from William & Mary’s Virginia Institute of Marine Science (VIMS) highlights the growing recognition that sea-level rise will mostly impact rural land—much of which is privately owned—where decisions involve complex tradeoffs between the value of different land uses. Many landowners see upland-to-wetland conversion as an economic loss, while wetlands provide valuable ecosystem services to the public by improving water quality, supporting marine fisheries and protecting against flooding.
The paper, which was recently published in the journal Nature Climate Change, is the first effort to synthesize the growing number of studies of land conversion driven by sea-level rise. In the Chesapeake Bay region alone, more than 150 square miles of forest have converted to marshland since the mid-1800s. Rates of forest retreat are accelerating around the world, with mid-Atlantic forests retreating inland more than twice as fast as they were 150 years ago.
“Uncertainty regarding local flood-defense strategies is the key thing that limits our ability to predict land conversion and its impact on coastal ecosystems,” Gedan said. “The process of upland conversion could offset or even overwhelm wetland losses expected within the next century, but is highly dependent on the decisions of rural private landowners.”
Gedan and her co-author, VIMS Associate Professor Matt Kirwan, note that the scientific community’s emerging recognition of this issue has generated widespread interest in better understanding the many factors that influence the extent and pace of upland-to-wetland conversion.
These include the rate of sea-level rise, slope of the upland, tidal range, amount of sediment available for vertical marsh growth, salt tolerance of different tree and grass species and—critically—the presence of levees and other human barriers both large and small.
Because landowner attitudes and experience with current mitigation efforts suggest local resistance, Gedan and Kirwan concluded their review with three recommendations to help guide future research and land-management decisions in rural areas:
- First, conduct additional studies on the effectiveness of privately maintained barriers such as berms and roads. The knowledge gained could minimize the cost of abandoning or restoring rural lands, and help landowners, government and environmental organizations prioritize conservation efforts.
- Second, study whether interim approaches—planting salt-tolerant crops, leasing land to hunt clubs, harvesting susceptible timber—can compensate for changes in the value of private property versus ecosystem services.
- Third, examine how policy incentives might shape the future of upland-to-wetland conversion. Offerings such as U.S. Department of Agriculture’s Conservation Reserve Program, in which farmers are paid to remove environmentally sensitive land from production, could be repurposed as instruments for adapting to sea-level rise. Gedan and her colleague also recommend that policymakers use regional predictions of wetland gain or loss to set incentives for prioritizing wetland migration or upland protection.
Sea-level rise, marked by ghost forests and abandoned farm fields, will mostly impact rural land—much of which is privately owned.