The United States National Arboretum is an arboretum in northeast Washington, D.C., operated by the United States Department of Agriculture’s Agricultural Research Service.

It was established in 1927 by an act of Congress[1] after a campaign by USDA Chief Botanist Frederick Vernon Coville.

It is 446 acres (1.80 km2) in size and is located 2.2 miles (3.5 km) northeast of the Capitol building, with entrances on New York Avenue, NE and R Street, NE.

The campus’s gardens, collections, and features are connected by roadways that are 9.5 miles (15.3 km) long in total.

In addition to the main campus in Washington, D.C., there are research locations at the Henry A. Wallace Beltsville Agricultural Research Center in Beltsville, Maryland and in McMinville, Tennessee.

The Arboretum functions as a major center of botanical research conducted by the USDA, including applied research on trees, shrubs, turf, and the development of new ornamental plants.

In addition to a library and a historical collection (archive), the institution also has an extensive herbarium of over 800,000 specimens documenting wild and cultivated plant diversity.

The arboretum is home to one of the largest collections of preserved seeds in the world.

The National Arboretum Herbarium houses around 700,000 specimens, including those from species that the U.S. Department of Agriculture views as economically important.

“One of the things that we focus on is collecting the genetic diversity within those species, and both native and non-native. So, our role, our goal and our mission is to conserve as much of the genetic diversity of those species as possible,” says Kevin Conrad, the arboretum’s lead horticulturist.

“We never know what the emerging threat will be. There is a chance that a gene from any of those collections would help resolve that issue,” Conrad says. “There are examples throughout the USDA history, in conservation and plant collection, where the gene in a wheat plant or a grape plant has been able to thwart a disaster, a catastrophic event, a collapse of a critically important agricultural crop.”

While the scientists do their work, the public is free to roam the arboretum grounds. About 600,000 people visit the gardens each year. That’s a fraction, for example, of the 25 million who visit the National Mall, which is a much better-known Washington attraction.

A sandstorm hits the northern Iraqi city of Mosul with local landmarks such as the Al-Nuri mosque and the Mosul Bridge shrouded in dust.

Last year, Iraq experienced more than a dozen sandstorms, an unprecedented number that was attributed to desertification.

Sand And Dust Storms Are Common Meteorological Hazards In Arid And Semi-Arid Regions.

They are usually caused by thunderstorms – or strong pressure gradients associated with cyclones – which increase wind speed over a wide area.

These strong winds lift large amounts of sand and dust from bare, dry soils into the atmosphere, transporting them hundreds to thousands of kilometres away.

The Main Sources Of These Mineral Dusts Are The Arid Regions Of Northern Africa, The Arabian Peninsula, Central Asia And China.

Comparatively, Australia, America and South Africa make minor, but still important, contributions.