By SHARON SETTLAGE
This article was published in the Spring 2012 issue of Coastwatch.
Burned feet. That’s what you can get if you attempt to make your way barefoot past the dunes on a hot summer day. Temperatures in the sand near dunes can reach 146 degrees.
But what about the beach grasses, like the beautiful sea oats rippling in the wind, that seem unbothered by the blazing hot sand? How do they survive the harsh combination of burning sand, sun and salt spray? Unlike most other plants, sea oats are adapted to those severe conditions — even prefer them.
A recent study funded by North Carolina Sea Grant found that Atlantic Coast sea oats are truly unique. Biologists Eva Gonzales and graduate student Richie Hodel at Appalachian State University used DNA analysis to study populations of sea oats, or Uniola paniculata, along the Gulf and Atlantic coasts.
The genetic evidence shows differences between populations within the species. These data might explain anecdotal observations that indigenous sea oats grow better in North Carolina than Gulf Coast sea oats.
Nurseryman Steve Mercer and others have known for years that sea oat seedlings are best raised from seeds gathered near the spot where they are to be transplanted. They cite lessons learned from the late David Nash, who was an N.C. Cooperative Extension agent for Brunswick and New Hanover counties.
“I expect that most Master Gardeners and nursery operators will recommend local stock for most species, including sea oats,” says Spencer Rogers, Sea Grant coastal construction and erosion specialist.
After Hurricane Isabel in 2004, many plantings on the Outer Banks required in-state seeds. “Later, the N.C. Department of Transportation planting specifications for Highway 12 required seed sources within 100 miles,” Rogers continues.
MORE SEA OAT SCIENCE
Back in the 1970s, Ernie D. Seneca, then at North Carolina State University, had Sea Grant funding to study dunes and dune grasses. Seneca collected seeds from Atlantic and Gulf localities and measured the growth rates of the sea oats under various temperature and light conditions. His study showed three growth types — a Virginia and North Carolina population, an Atlantic Coast Florida population and a Gulf Coast population. Georgia and South Carolina sea oats were not included in his study.
A Florida Sea Grant-funded study in 2004 at the University of Florida also found that geographic source was significant in affecting sea oat growth rates when planted in different locations. One of the researchers, Michael Kane, was instrumental in providing Florida sea oat samples for the Appalachian State study.
The recent work by Gonzales and Hodel is unique because they used modern DNA sequencing to show genetic differences in plants from different localities.
Their study indicated that Gulf Coast and Atlantic Coast sea oats are different on a genomic level. The research team sampled leaves from sea oats in Texas, Louisiana, Mississippi, Alabama, east and west Florida, Georgia, South Carolina and North Carolina.
A NEEDLE IN A HAYSTACK
Graduate student Hodel had a formidable task before him when he started his project work in Gonzales’ lab in winter 2009. Gonzales had samples of geographically spaced plant material, the sequence of sea oat chloroplast DNA, and a hunch that there might be different DNA sequences between Gulf Coast and Atlantic Coast sea oats. She had no idea what, if any, differences there might be.
Much like a forensic criminologist would identify an individual suspect, Hodel performed PCRs, or polymerase chain reactions, and sequenced DNA from chloroplasts to find specific differences among individual plants. Amongst the 16,000 base pairs of DNA that he sequenced, he found five nucleotide differences.
Once he knew he could detect genetic differences, his job shifted to the field. Hodel drove to the coasts of Texas, Louisiana, Mississippi and Alabama to sample plants every 50 kilometers — about 31 miles — or so.
Louisiana, he said, was the most challenging, because many areas were swampy and without dunes. No dunes means no sea oats.
Other samples were provided by scientific collaborators or were previously collected by Gonzales. Most North Carolina samples were obtained during beach trips by Hodel or his lab mates.
Back at the lab, Hodel used computer analysis to show that the five genetic differences between his plant samples could be boiled down to two distantly related populations: a Gulf Coast or western lineage and an Atlantic Coast or eastern lineage.
Gonzales and Hodel speculate that the mangrove forests of southern Florida formed a natural barrier that isolated the plants during millions of years of sea oat evolution. Without intermixing, the chloroplast DNA sequences drifted into two major genotypes.
Given their scientific evidence indicating that sea oats are genetically different, Gonzales and her team concluded that sea oats from the Gulf Coast are best kept on the Gulf Coast and Atlantic Coast sea oats should not be planted on the Gulf. However, their sampling indicated several cases of intermixing in man-made restored dunes. “There is an area around Charleston, S.C., that is so mixed up. They had planted everything,” Gonzales says.
Gonzales plans to take advantage of the “mixed-up plantings” in the Charleston Harbor area to study whether locally adapted plants are truly better. If the hypothesis that local plants grow better is correct, then her team will find that the Gulf Coast type performs more poorly on the Atlantic Coast than native plants. “The experiment has already been planted,” says Gonzales.
This is not a new idea — Rogers and Nash recommend in The Dune Book to use transplants obtained less than 100 miles from the area to be planted. But the concept has yet to be proven and documented using modern scientific techniques. Gonzales’ work promises to make significant progress in this area.
Mercer, part owner at Coastal Transplants in Bolivia, near Wilmington, credits Nash for emphasizing the use of locally adapted plants. “There was a time period when that question was never asked,” Mercer says.
The family-owned business took Nash’s advice to heart and is careful to collect and maintain supplies of sea oat seeds from islands along the coast. They keep 6-pound bags of pure seed collected from locations as far as Texas to the closer barrier islands of North Carolina.
Germinating the seed is no simple matter. A few years ago, only one out of 10 seeds planted was expected to grow. Coastal Transplants has improved germination rates over the years with a specialized growth room for seed germination.
After emergence of the first leaf, the tiny plantlets are moved to a high-humidity, 80-degree greenhouse. Here the major enemy is mice, which can decimate a planting overnight.
Hurricanes are not friends to the plants either. In January, Coastal Transplants was still recovering from Irene’s work last year. The storm ripped the plastic roofs from the greenhouses.
However, traditionally, 18 months or so after a hurricane, when emergency funds have come through and municipalities are ready to rebuild their dunes, sea oat growers are glad to provide the plants.
Mercer is delighted to hear of Gonzales’ DNA work. “It would be nice if somebody could do DNA here and go to their greenhouse and do DNA there,” he says. “Before that plant’s ever planted on an island, the DNA is done.” That way, a municipality might discover that plants being marketed as, say, Ocracoke Island plants are actually Florida plants.
“It’s nice to know that there’s that capability out there,” Mercer says.
Sea oats are a signature species in the dunes from southern Virginia to the southern tip of Florida and in beaches along the Gulf Coast. What is special about their environment? Salt, wind, ocean waves, hot sun — conditions where most plants whither and die.
Sea oats and other common dunedwelling species, such as American beachgrass (Ammophila breviligulata) and bitter panicum (Panicum amarum) have the unique ability to withstand and even thrive in the hot, dry conditions.
Rogers recounts an incident where he was called upon to give a coastal property owner advice on growing sea oats that “weren’t perky.” Upon further investigation, Rogers found the dune grass planted among healthy tomato and chrysanthemum plants that were thriving under a regime of regular irrigation and fertilization. The problem, says Rogers, was the rich growing conditions. Sea oats are poor competitors. Next to the vegetables and flowers, they lose out.
The Dune Book advises that healthy dune plants are better off left in the harsh conditions where they prefer to grow. The authors, Rogers and Nash, note “excessive irrigation allows other species to compete with dune vegetation by rinsing the salt spray off the leaves and out of the soil.”
PROTECTION AGAINST STORMS
Not only are sea oats beautiful to look at, they also are important in helping to establish sand dunes. Rogers and Nash write, “Plants trap blowing sand, causing the formation of sand dunes and stabilization of barrier island soils.” The dune also provides a habitat for animals such as birds, amphibians and reptiles.
Large dunes are not readily eroded by storms and protect areas further landward from storm surge. “A principal benefit for anyone living near a shoreline is that the dune acts as a storage reservoir for sand… If the dune is large enough, waves and storm surge are prevented from washing across a barrier island,” the authors add.
Likewise, Mercer points out that dunes act as a buffer against storm damage. Municipalities are wise to invest in dunes. He suggests that they spend money to build vegetation, which then builds sand. The sand dunes build a time buffer between when the storm hits and when it leaves.
“If you can build a three- to four-hour buffer, you may have potentially saved a lot of money and inconvenience. If it takes two to three months to get that road built back, think about the loss of rental income and think about how many people depend on the rental income to make the mortgage on the house,” Mercer explains.
However, a significant storm event may completely erode protective dunes. In this case, wise property owners can build an artificial dune following state and local regulations. Permits may be required for certain dune construction projects such as the use of sand fences, walkways or ramps.
If some vegetation remains from the old dune, it will trap blowing sand and eventually reform the dune naturally.
In The Dune Book, Rogers and Nash recommend placing a man-made dune as close as possible to the area to be protected, far from any potential shoreline. Rather than scraping the beach for sand, it is best to use beach-quality sand purchased from an inland source.
With the sand in place, it is imperative to plant dune grasses to encourage further trapping of wind-blown sand.
Rogers recommends sea oats as the best choice for areas south of Cape Hatteras. North of Hatteras, dunescapers may choose American beachgrass, which is better adapted to cooler temperatures and can form a very dense stand. American beachgrass is still a good choice for quick stabilization of dunes south of Hatteras, but sea oats should be included for long-term stability.
Dunes with sea oats provide benefits on so many levels. They are an ecosystem for a variety of plants and animals. They buffer structures against storms. They are aesthetically pleasing.
Mercer notes that many municipalities are beginning to look at their beach as infrastructure, and budgeting to maintain those beautiful dunes. In the colorful words of Mercer, “I have never seen anybody spend $4,000 a week for a house, drive all the way from Ohio, and put their lawn chair on the road to see the garbage truck pick up garbage. They come because of the beach.”
To find local sources of dune plants, contact Spencer Rogers at: email@example.com or 910/962-2491.
For more information, read The Dune Book at: ncseagrant.org/s/dunebook. Copies are available as free downloads.
Look for Karl Graetz’s book, Seacoast Plants of the Carolinas (UNC-SG-73-06), at your local library. Limited copies are also available from North Carolina Sea Grant. Send an e-mail to firstname.lastname@example.org or call 919/515-9101 to confirm stock availability.
This article was published in the Spring 2012 issue of Coastwatch.
For contact information and reprint requests, visit ncseagrant.ncsu.edu/coastwatch/contact/.