The changing natural world at our doorsteps | By Patterson Clark
June 21, 2011
Securing the lizard's tails of Huntley Meadows
When summer officially begins at 1:16 p.m. today, a sun-loving wetland plant will be at peak fragrance.
Lizard's tail stands a yard tall, has heart-shaped leaves and floppy white flower stalks that begin to release a sweet perfume in
The plant probably gets its name not from
its bottle-brush flowers, but from its fruits, which will mature in the fall. By then, the flower stalk will be covered with tight brown seed capsules resembling the scales of a reptiles tail.
One of the best places to experience lizard's tail is at Fairfax County's Huntley Meadows Park, a 1,500-acre tract of lowland timber and freshwater wetlands north of Mount Vernon. The plant grows
profusely along the boardwalk that snakes through the marshes, which were created more than 30 years ago by beaver dams.
But the marsh is changing, becoming less suitable for lizard's tail. As silt accumulates and beavers begin to exhaust their available tree supplies, the marsh gradually transforms into a drier habitat known as a wet meadow, which would eventually grow trees again.
Because the park holds the county's only large non-tidal marsh, park managers want to restore and maintain the wetland's native biodiversity, which reached its highest level in the 1980s. That can happen only with a balance between open water and vegetative marsh.
By the end of 2013, a textured, mud-colored
concrete dam with pipes will be added to the network of beaver dams, allowing managers to adjust water levels so that wetland animals and plants such as lizard's tail can continue to thrive in the future.
SOURCES: Kevin Munroe, manager, Huntley Meadows Park; Fairfax County Park Authority; Friends of Huntley Meadows Park
June 28, 2011
Upgrading the lawn at the National Mall
Some turf panels are long, some are short.
The Smithsonian Folklife Festival will soon
blossom on the Mall, drawing 2 million feet that will trample the turf and pack down the soil, which is already so dense and compacted that it's almost as hard and impermeable as concrete.
The grass gets little help from the Mall's irrigation system, which has been damaged by trucks driving across the surface and tent stakes puncturing the pipes. As a result, the National Park Service must manually irrigate the exhausted turf.
But greener days are on the horizon for the Mall's turf panels, the open, grassy fields at the eastern end of the Mall. In September, contractors are scheduled to begin renovating the panels, beginning with eight of them between 3rd and 7th streets. That phase of the project should be complete by October 2012.
The top six to 18 inches of soil will be enhanced with a mixture of coarse sand and compost, which will alleviate compaction and increase water permeability.
Panels will be raised 2 inches higher than surrounding walkways and each panel will be
edged by a granite curb-and-gutter system to
channel rainfall runoff into underground concrete cisterns, which will supply water for a new, more durable irrigation system.
Although the turf will still host high-impact events, the grass will recover quicker than before.
SOURCE: National Park Service
July 5, 2011
Bitter dock's tiny, patient seeds
Standing in sharp contrast to the deep greens of July's sunny fields, the rusty-brown seed heads of bitter dock ripen and begin to loosen their grip on thousands of small, dry fruits.
Weak spines on each fruit the seed and its papery covering can briefly latch onto a passing dog or pants leg, which can ferry a fruit well away from its parent plant. The fruits can also ride the wind for a short distance or float for miles on a river surface.
Each fruit contains a single, sharp-angled, 1/16-inch-long three-sided seed, which probably won't sprout until the weather cools down. Bitter dock seeds germinate best in bright light, so if a seed becomes buried, it may not get the opportunity to sprout for a very long time. But it can wait . . . and wait, remaining viable in the soil for more than 50 years.
Once abundant in the eastern United States, the rusty-patched bumblebee has almost vanished.
July 12, 2011
Plight of the bumblebee
That tomato ripening in your garden probably got its start after a visit from a bumblebee.
Tomatoes, potatoes and other plants in the nightshade family are best fertilized by "buzz pollinators" such as the bumblebee, which will clinch a flower in its jaws and rapidly vibrate its wing muscles to give the blossom a good shake.
This rattles loose pollen that collects on the bee's pile, or hairy coat. The bee will carry most of it back to the hive and pack it with nectar into a brood cell for bee larvae to eat.
Bumblebees are such effective pollinators that they have been raised commercially for use in produce greenhouses a practice that may have precipitated a rapid decline in some wild bumblebee populations.
Bees sent to Europe for commercial breeding may have returned to the United States with a microsporidian parasite, which could be responsible for decimating several species of bumblebees. Other possible contributing factors: global warming, fragmented habitats, pesticides and a lower genetic diversity in those bumblebee species that are in decline.
Sources: "Patterns of widespread decline in North American bumble bees," Proceedings of the National Academy of Sciences; The Xerces Society for Invertebrate Conservation
July 19, 2011
With DAN KEATING THE WASHINGTON POST
Washington's improving air quality
When summer's heat roasts the Washington area, air quality tends to worsen but compared with a decade ago, it has improved.
"We still get bad days," says Timothy Canty, an atmospheric scientist at the University of Maryland, "but it's getting better." A 2002 EPA regulation required states to reduce emissions of nitrogen oxides (NOx). On hot, stagnant days, NOx and volatile organic compounds (VOCs) produce ozone (O3).
"Ozone is a good thing at high altitudes, where it blocks damaging ultraviolet rays," says Canty, "but at ground level, ozone inflames the lungs." It causes acute respiratory problems, reduces lung capacity and impairs the body's immune system. "In some cases," says Canty, "high ozone levels can lead to death." Ozone can also damage vegetation, including crops, and it will degrade rubber and plastic.
Alerting the public to air-quality dangers, the Metropolitan Washington Council of Governments (MWCG) issues a daily air-quality forecast, which gauges the presence of ozone and aerosols, airborne particles resulting from combustion, especially from industry and vehicles.
SOURCES: Environmental Protection Agency, District Department of the Environment, Metropolitan Washington Council of Governments, Clean Air Partners
July 26, 2011
Summer's wild oats, winter's warm mush
Throughout the summer, the flattened green flower spikelets of wood oats dangle from gracefully arching peduncles.
As autumn approaches,
the spikelets bearing ripening seeds turn blond, then bronze, and finally fade to gray in the winter. Their durability and pleasing form make them a favorite with flower arrangers, who sometimes refer to the plant as spangle grass or wild oats.
Also known as river oats, the plant has salt-, shade- and drought-tolerant qualities that are praised by landscape designers and by land managers who use the grass to halt erosion or stabilize sand.
Scientists are eyeing the tough traits of the grass to possibly exploit them for modern agricultural purposes, but use of the plant for food stretches back for centuries. The Cocopa tribe from the Southwest stored the meager seeds for use in winter, grinding and cooking them for porridge.
SOURCES: Proceedings of the National Academy of Sciences, University of Texas, University of Michigan
August 2, 2011
Killer graffiti: Opening a door to beech bark disease
Memorializing summer love by cutting initials into a tree may seem like a harmless romantic gesture, but knife marks can spell death for a smooth-skinned stately beech. Such an act can set the stage for infection, especially by deadly beech bark disease, or BBD.
Carving into the tree "creates a rough spot in the bark, which gets rougher as the tree grows," says Mark Twery, a researcher with the U.S. Forest Service. "Those rough spots are precisely the places where the beech scale can find a place to shelter and attack the bark."
When the scale (an invasive European insect) sucks sap from the bark, "it actually alters the physiology of the tree, making it susceptible to the fungus that causes BBD," says Twery.
Sometimes a tree can seal off a fungal infection, but the disease tends to kill about half of the mature beech trees once it enters a forest. Only about 1 percent of beech trees are resistant to BBD.
The disease arrived in North America in the 1890s on European beech trees that were planted at the Botanical Gardens in Halifax, Nova Scotia. Since then, BBD has swept across New England, down through New York and Pennsylvania, and has spread as far west as Wisconsin and as far south as the Great Smoky Mountains,"most likely by people moving firewood for camping," says Twery.
While the disease may not have entered the Washington area yet, it might be only a matter of time before local beeches become infected. The biggest threat: people transporting firewood from infested areas back to their city homes, "the same problem," says Twery, "that is causing the spread of emerald ash borer and Asian longhorned beetle," two other exotic insects now threatening to wipe out North America's ash and maple trees.
Source: U.S. Forest Service
To immortalize a romance, some people choose to plant a young tree, rather than knife an old one, such as this beech in the District's Whitehaven Park.
August 9, 2011
A drier August: the new normal
With Dan Keating / The Washington Post
Washington's August has dried up.
What was once the rainiest month of the year is now one of the driest. It has become a month marked by withering foliage and aborted blooms.
Average rainfall at Reagan National Airport in August has fallen from almost five inches in the middle of the last century to less than three inches today. The tropical storms that used to roll through the area bringing 12 and 14 inches of rain at a time have tapered off. The most rainfall August has seen since 1980 was seven inches in 1990. And in the past decade, August has exceeded five inches of rain for the month just once.
"That is quite an eye-opener," says Mike Hapert, deputy director of NOAA's Climate Prediction Center. "My recollection has been that August has been one of the wettest months."
So what happened?
Experts at the center are reluctant to point to a reason. "It could be chance that there weren't any" tropical storms recently, says Dan Collins, a meteorologist with the center. "I am sure that there is no good evidence that [human-caused global warming] caused the change."
Rick Schwartz, a weather historian and author of "Hurricanes and the Middle Atlantic States," calls it remarkable that so few hurricanes have made it to the East Coast during the past decade, even though the North Atlantic is in the midst of an active hurricane period. "Hurricanes are either weakened or turned out to sea," he said, speculating that the region's increasingly hot weather seems to be acting as a shield, which keeps hurricanes away.
"But if there is a cause and effect," he said, "it definitely won't be established for a long time."
Whatever the reason, a drier August has had a significant impact on plant and animal life in myriad ways.
Because most of the growth for many summer crops is in June and July, less rain in August has little impact on yield if rainfall is near normal the rest of the summer, says Robert James Kratochvil, a University of Maryland agronomist.
Less rainfall might even be good for some wetlands. Lower water levels can open up large areas usually inundated in late spring and summer, says Changwoo Ahn, a wetlands ecologist at George Mason University. This would trigger germination and growth of a variety of moist-soil plants that would otherwise have been still dormant, Ahn said. Such a vegetative explosion would enrich the wetland's diversity and productivity.
But a boost for wetland plants might come at the expense of some wetland animals: Bullfrog tadpoles need water in August to complete their development, says Kevin T. Munroe, manager of Huntley Meadows Park in Fairfax County. "Although we still have a strong bullfrog population, we do appear to have less now than we did 15 years ago," he said.
"There are also several species of dragonflies that lay their eggs in shallow, late-summer wetlands," he adds. He has noticed fewer bar-winged skimmers whenever August is dry.
Perhaps one of the most visible effects of a drier August can be seen in the oaks, says Rod Simmons, a plant ecologist with the city of Alexandria. "Oaks are generally drought-tolerant," he says. "But they do require sufficient and consistent moisture during growing season for good health and long-term survival."
He called the extensive crown dieback of numerous old-age oaks throughout the region a sign of doom for the trees.
There could be hope, however. Although Northern Virginia still has an August rainfall deficit, Maryland's regional totals have been above average for the past two years. Could this be the start of an upward swing?
*Comparing difference in normal rainfall between the periods of 1900-1980 and 1981-2010.
Labeled changes are statistically significant within a 90% confidence interval.
Bold labels indicate significance within a 95% confidence interval.
August 16, 2011
Raccoon roundworm: The hidden danger in raccoon latrines
As slightly cooler weather coaxes people back outdoors to play or tend to their gardens, they would be wise to be on the lookout for an insidious danger: communal raccoon latrines.
It's not the raccoons themselves that present the threat; rather, it is their intestinal worms, a parasite that infects more than half of the raccoon population and can be deadly to humans.
Raccoon roundworms release millions of microscopic eggs, which permeate the mammal's feces. Once released, infectious larvae can survive for years in their protective eggs until a bird, small mammal or human ingests them.
If worm larvae hatch out in an animal other than a dog or raccoon, they can be carried through the bloodstream to various parts of the body, where they can bore into muscles, vital organs, eyes or even the central nervous system, causing a devastating encephalitis.
Confirmed human cases are rare, but infection is very difficult to diagnose. Treatment tends to be successful only if the infection is treated during its early stages.
Children are at a higher risk of infection than are adults, since they are more likely to ingest contaminated soil. People should always wash their hands after working in the garden or rearranging the woodpile.
Parents can steer kids clear of the threat by first scouting for latrines, which are recognizable by their generous assortment of raccoon scat:
small, dark, smelly cylinders, blunt at the ends and often filled with seeds.
People who find coon scat on their decks or
patios can dispose of the droppings in a plastic bag and disinfect the area with steam or boiling water.
SOURCES: Centers for Disease Control and Prevention; Parasites: Tales of Humanity's Most Unwelcome Guests, by Rosemary Drisdelle
Forget about trying to rid the neighborhood of raccoons. They're smart, secretive and
adaptable, and they thrive in urban areas, finding an abundance of food and shelter.
People can, however, take steps to discourage their presence:
♦ Ensure that no raccoons are present in attics, chimneys or sheds, then seal any access points
to prevent their nesting or defecating there.
♦ Collect and freeze all meat scraps, bones and grease in a screw-top plastic container before setting these food items out in the trash.
Compost vegetable waste in a mammal-proof compost bin.
♦ Don't leave pet food outdoors.
♦ Raccoons are attracted to water, so families with small children may want to rethink that birdbath or fishpond.
August 23, 2011
Ironweed: A flinty flower
It's tall and it's tough, and it's probably more welcome in the city than in the country.
Ironweed was named for its rugged stalks, which stubbornly persist throughout the winter. Its underground stems are equally tenacious, sending up sprouts even when repeatedly mowed.
The plant's vivid purple flowers may look lovely in a cityscape, but they are a bane in the pasture. Cattle and horses won't eat the bad-tasting leaves, which allows the plant to spread and crowd out vegetation more suitable for grazing. (Deer avoid ironweed, too another good reason to include the native plant in a flower bed.)
But goats will munch away on ironweed, prefering it to grass, so some ranchers include goats with their cattle herds to keep the weed under control.
The tough digestive system of goats can tolerate the bitter compounds in ironweed leaves, which repel most insect and mammal herbivores.
Some ironweed compounds were used in the past to prevent atherosclerosis and alleviate the pain of childbirth. Extracts from ironweed also have shown promise in treating malaria and reducing the desire to smoke tobacco.
SOURCES: Ohio State University, Journal of the Arnold Arboretum, Western Kentucky University
August 30, 2011
Mallards: Birds of a feather that change with the weather
Distinguishing drakes from hens is easy in the spring: Drakes have iridescent green heads, hens are brown. But by late summer their distinctive plumage is blurred by molting and an abundance of juvenile ducks that look a lot like Momma.
Early in the summer, the drake abandoned the hen and her nest and began his first molt to enter eclipse, where he became flightless, reclusive and covered in brown feathers. He has now rejoined the sord and is molting again, reclaiming his green head, ringed neck, burgundy chest, gray sides and curly black tail.
The hen molts only once, late in the summer, shedding her brown-streaked camouflaging feathers for more of the same.
Juvenile ducks can be recognized by their brown outer tail feathers. Adults' are white. First-year birds will also molt before autumn, retaining flight feathers while replacing body feathers. Young males will transform into a pale version of their fathers. Female juveniles will look pretty much the same as before.
Beak color is the most reliable way to sex a mallard. Males have greenish-yellow bills, while females sport orange bills with black splotches.
September 6, 2011
Sorting out the scales of magnitude
In the past, that number would have been determined simply by how much an earthquake moved the needle on a seismometer. The size of the jolt was then assigned a position on the Richter scale, a logarithmic chart on which each step is ten times more jarring than the previous step.
But for earthquakes larger than 3.5, seismologists now use the moment magnitude scale, which represents the amount of energy released during an earthquake. In use since 1979, the scale factors in a fault's rigidity, the area of its rupture surface and the distance that the earth moves along the fault.
While the shaking of a 6.0 magnitude quake is ten times greater than that of a 5.0 as in the Richter scale the
amount of energy released is 32 times greater. A 7.0 will shake 100 times worse than a 5.0, but the energy released is a thousand times greater.
The diagram at right uses spheres to compare relative amounts of energy released by earthquakes. Each sphere represents the amount of TNT that would be required to release as much energy as a quake of the specified magnitude. The Washington Monument is thrown in for scale.
September 13, 2011
Goose grass: A county tough comes to town
A cropland pest is also the city's toughest weed, holding its own even when growing from the crack of a heavily trafficked sidewalk or parking spot.
Even where it isn't being trampled, goose grass grows flat to the ground, its pale silvery stems forming a coarse starburst that can duck the lowest of lawn mower blades.
If a hoe doesn't get to it first, the grass will meet its match when freezing temperatures knock it out. But by then the weed's zipper-shaped spikelets will have dropped hundreds of tiny, dark-brown seeds. Those will sprout best late next spring on the sun-drenched surfaces of compacted city soils and country croplands, where goose grass is developing resistance to a growing number of herbicides.
Although goose grass is one of the world's worst agricultural weeds, its measly seeds can become a grain of last resort during a famine. If enough seeds are gathered from plants growing in uncontaminated soil they can be boiled whole or ground into flour for making cakes or gruel.
September 20, 2011
Troubled urban streams
When hurricanes or tropical storms pass through the Washington area, flash flooding can become a problem, not just for houses and businesses in the flood plain, but also for the organisms that live in the waterways being flushed with storm water.
The flow can cause serious disturbances in streambeds, "uprooting aquatic plants, rolling rocks and killing many bottom-dwelling organisms," says N. LeRoy Poff, an ecology professor at Colorado State University.
Heavy rains can also flush pollutants and soil sediments into streams. Although too much sediment in a stream can cause problems, too little can also be detrimental.
"Many streams inside the Beltway have been urbanized for a long time, and there is no longer available sediment from the watershed due to all the impervious surfaces," says Poff. A loss of sediment cripples an urban stream's ability to deposit new banks and bottoms, so the stream becomes incised, cutting an increasingly deeper groove for itself.
Another problem: Roofs, streets and parking lots prevent rainwater from soaking into the ground, sending it as a "flash" through urban waterways. Sensitive species have trouble finding refuge during such an event.
Only species that are pollution-tolerant, have a fast life cycle and are able to handle extremes in flow can survive in such an environment, says Poff.
Carlisle describes urban-stream fishes, such as the common carp, as generalists: "They can reproduce anywhere and eat anything."