Turn off a nondescript highway in Prince George's County, pass through an electronically controlled gate, drive a mile on a rutted one-lane road, and you'll find America's response to agricultural Armageddon.
Here, on the south side of the Beltsville Agricultural Research Center, researchers are raising trees from seeds in one of 28 federal repositories set up to ensure survival of the planet's agricultural products - and the humans who depend on them.
These 64 acres of trees and shrubs, along with the seeds that produced them, contain genetic weapons to battle the droughts, blights and bugs often brought on by invasive species, habitat loss and climate change.
"Everything is under threat, everything," said Kevin Conrad, 45, curator of the center's repository of woody landscape plants and seeds. Scientists say they can use the seeds to serve up replacement crops and develop hybrids capable of resisting current and future pests and pathogens.
Conrad directs this effort from a trailer surrounded by 5,700 trees and shrubs sown from the Beltsville seed bank. Some are also displayed at the National Arboretum in Washington.
In one row are hemlocks, maples and lilacs from the mountains of China. In another, apricot trees from Japan grow near a Korean snowbell, a bush-like tree imported as an alternative to the American dogwood. Nearby is a Kentucky coffee tree, named for the pods that can be ground up for a brew that you won't find at Starbucks.
"I've never tried it, but I've heard it tastes terrible," Conrad said.
A few miles north, behind locked doors, near the end of a dimly lit corridor, Conrad and colleagues keep the seeds packed in heat-sealed plastic bags in a closet-sized refrigerator.
"It's fundamentally important work," said Stephen Smith, a research fellow at Pioneer Hi-Bred, an Iowa-based seed company.
The seeds are intended to combat pests such as the emerald ash borer, a voracious beetle that has killed 20 million ash trees since it spread east from Michigan in 2002, prompting federal quarantines in the Midwest and parts of Prince George's County.
Another target is the woolly adelgid, a Japanese import that has killed hemlocks in 17 states along the East Coast since it was discovered in Virginia in 1951. "We're trying to find a hybrid that can resist it," said Anthony Aiello, curator and director of horticulture at the Morris Arboretum of the University of Pennsylvania, who has tapped into the Beltsville collection for research.
Seed bankers have their heroes. At the German siege of Leningrad during World War II, a team of Russian scientists elected to starve to death rather than eat seeds from the famous seed bank started by Russian botanist Nikolai Vavilov in the 1800s.
But these days, risks are generally limited to the hazards of long-distance travel. Conrad searches overseas for temperate climate trees and woody ornamental plants. He was in Azerbaijan in the summer of 2006 and has traveled several times through the Caucasus, the area between Turkey and Russia where the climate is Maryland-like and many of the Beltsville plants originated.
His colleague, Martin Scanlon, has made several trips to Russia in search of hemlock trees with ancient lineages. "We go pretty much anywhere in the temperate world where we can find plants," Scanlon said.
Researchers keep the seeds for 10 years and, like canned goods in a kitchen pantry, they are constantly replenished. Other Department of Agriculture sites have different specialties: Tropical ornamental plants are stored in Miami; apple and grape seeds are protected in Geneva, N.Y.
A backup collection for all 28 sites is at Fort Collins, Colo., where storage facilities can keep seeds viable for 100 years.
Seed storage is a matter of basic biology. A seed is a plant's embryo - protected by a coating until the right levels of moisture and heat make it germinate. To prevent germination, most seeds are stored in Beltsville and Fort Collins at zero degrees Fahrenheit.
At Fort Collins, scientists also plant stored seeds every 10 to 15 years to make sure they're viable, according to curator David Ellis. If tests show that less than 60 percent are germinating, fresh crops are planted and their seeds are shipped to Fort Collins.
Since humans began farming about 10,000 years ago, crops raised for food and fiber have developed a range of genetic weapons to resist pests and pathogens, Smith said.
But 30 to 40 years ago, researchers began developing hybrid agricultural crops and horticultural plants to maximize productivity. They selected traits that increased quality and productivity - and helped feed the world, Smith said. But the work also narrowed the genetic range of many crops, making them more vulnerable to attackers.
"We have a lot of invasives that are threatening a lot of our native plants, and things can get wiped out," said Scott Schlarbaum, a forest biologist at the University of Tennessee.
The federal seed bank network was established in 1980 to help preserve the genetic diversity of the nation's flora.
"When you lose diversity, you lose the opportunity to find a drought-resistant gene or an insect-resistant gene. It's advisable to keep all your options open," said Pioneer's Smith. "If agriculture fails, economies fail."
Experts say climate change also makes seed storage critical. New varieties of crops that can adapt and survive in changing climates could be a necessity. "The pressure to breed plants that will be able to adapt is going to be a major challenge," said Ellis, the Fort Collins curator.
The USDA seed bank is among the most comprehensive of the 1,400 private and public seed banks around the world, experts say.
Some are intended to preserve locally grown plants; others, like the USDA collection, include a sampling of crops that feed the world - an insurance policy for a planet threatened by warmer temperatures.
The newest seed bank, opening in February, is a vault carved from a mountain on a remote Norwegian island above the Arctic Circle. There the Global Crop Diversity Trust will house seeds from all over the world, including the U.S. "This is really a safety net," said its executive director, Cary Fowler.
Elsewhere, volunteers and staff from the Chicago Botanic Garden have spent four years collecting seeds from 1,500 species of prairie grass, which have largely disappeared from the Midwest.
The effort will continue throughout the Midwest until 2010, said Kayri Havens, the garden's director of plant science and conservation. In addition to storing seed in freezers, scientists are distributing it so it can be raised in parks and other public lands.
"I see it as kind of an insurance policy against extinction," Havens said.