GRASSES THAT FIX SAND DUNES

Charles J. Whitfield, Robert L. Brown

SAND DUNES have been a problem for centuries. The earliest modern reference to dune control was in 1316 in Germany. Laws limiting the use of dune lands have been enacted in nearly every country. The best estimate as to the area of the earth covered by sand dunes is 3,200,000,000 acres nearly twice the total area and seven times the agricultural land area of the United States.

Sand dunes in the United States, not including those in deserts, occupy an area one-tenth as large as the area of agricultural land. These dunes are found along the coasts, bordering the Great Lakes, and in practically all of the inland States.

Permanent control of active sand dunes can be accomplished only by establishing on them a vegetative cover, either by natural succession or by seeding. Mechanical structures stop sand movement only temporarily.

Grasses have a major role in the fixation of sand dunes, but only a few grasses are widespread and important on these sandy areas. For example, on the Pacific and Atlantic coasts and on the shores of the Great Lakes, beach-grasses grow either as native or naturalized plants. Dune-control work during the past 200 years in this country has established the value of both American beachgrass and European beachgrass on these coastal areas and for inland dunes.

Purple beachpea, a legume native on the Pacific and Atlantic coasts and along the Great Lakes, has been used successfully in mixtures that give permanent cover on the dunes.

In the Middle West and the Great Plains States, switchgrass, big blue-stem, sand bluestem, Indiangrass, and giant sandreed grass are outstanding. Sand blowout grass, sandreed grass, and yellow lyme grass were among those listed as important dune-control plants in the 1894 and 1898 Yearbooks of Agriculture. These are found to be less effective, however, than switch-grass, big bluestem, giant sandreed grass, and Indiangrass for permanent fixation.

Among grasses that assume considerable local importance are side-oats grama, sea-oats, sand lovegrass, weeping lovegrass, iceplant, and a strain of mammoth wild-rye.

Indian ricegrass and sand dropseed are well adapted to sand-dune conditions. They are primary invaders into temporarily controlled dunes but tend to disappear when competition becomes great, so that areas of sand often are left unprotected.

Most of the active sand dunes in the United States are caused by man's abuse of the protective vegetative cover. The goal in dune control is the reestablishment of a dense, permanent cover of vegetation. The cover may be herbaceous (grasses and legumes) or woody (shrubs and trees). These types are not easily or quickly established on infertile eroding sands subject to high-velocity winds. Provisions must be made for stilling the sand and for the orderly building up of the fertility and organic matter in the surface until vegetation of permanent types can be Planted. Permanent fixation of dunes has been efficiently accomplished in recent years in a number of localities.

Coastal sand-dune control in the cool temperate regions is illustrated by the Warrenton Dune Control Project at the mouth of the Columbia River in Oregon. Encroaching dunes were menacing agricultural lands, forts, military reservations, highways, towns, and resort homes valued in all at many millions of dollars. The dunes were also threatening to impede annually the movement of nearly $300,000,000 worth of ocean-going commerce moving at the mouth of the Columbia directly in the path of the encroaching dunes.

Dune-control work was started in July 1935. The men in charge first studied the factors they believed contributed to the continuance of active dunes by destroying vegetative cover: Fire, grazing by livestock, construction of roads and buildings, cultivation of sandy soils, and so on. They also investigated the jetties at the mouth of the river that alter the ocean currents, because they cause scouring of the ocean bottom and wash sand shoreward to cause dunes faster than vegetation can stabilize them. The causes determined, work was started to establish a permanent plant cover according to the needs of the land.

In most cases permanent cover was obtained in only two stages after the source of incoming sand had been controlled by mechanical devices or by vegetation. The first stage required sand-stilling plants. The final . stage was -the seeding or planting of permanent vegetation grasses and legumes or woody plants.

American beachgrass, European beachgrass, and American dunegrass were used effectively for the first stage of control. The first has been outstanding because it spreads by vigorous rhizomes and can persist longer than the other species.

The first year, fertilizer applications that provided 40 pounds of nitrogen an acre insured a better sand-stilling cover and made possible early seeding of the permanent cover. Seedings of permanent species were usually made at the end of the first growing season where beachgrass plantings had been fertilized. Such seedings could not be made before the end of the second or third year without this fertilization.

Native species were good for use in the permanent stage of control, but they were expensive and scarce. On the basis of several trials, the following combination of native and commercially available species was selected and used for final control: Tall fescue, Clatsop red fescue (a strain developed on the job from native stands), common ryegrass, purple beachpea, and hairy vetch. The vetch was the key to successful establishment of grasses; the beachpea provided the long-lived legume in the mixture.

As in the first-stage plantings, a fertilizer application at seeding time assured success with permanent seedings if the vetch was included. An application of 300 pounds an acre of ammonium phosphate (16-20-0) gave best results. Seedings without vetch failed. The vetch provided protection against wind and intense light, protected the more slowly developing species, and supplied organic matter. Seedings were made in the early fall in the mild climatic conditions that exist on the west coast. Stabilization progressed rapidly, and the shifting dunes were tied down with vegetation.

The plantings are being maintained to assure permanent dune fixation and give protection to farm, military, and other properties to the leeward.

Similar work has been done on the dune areas of Michigan, New York, and Massachusetts, and at other points along the Pacific and Atlantic coasts; slight variations in planting and management from those at Warrenton were due to differences in proposed uses of the land, type of sand, climate, and plants used.

Sand-dune control in the Great Plains area is typified by the Dalhart Sand Dune Stabilization Project in the Panhandle of Texas, and the Caddoa Sand Dune Stabilization Project in southeastern Colorado.

In 1936 studies were started near Dalhart to determine ways and means of stabilizing and utilizing sand-dune areas in the Southern Great Plains. The method developed for dune fixation included five steps: Controlling the critical or contributing area; deep listing between and around the dunes to catch the dune sand; breaking down crests and lowering the dunes to a point where they could be planted; establishing temporary control on the loose drifting sands by planting cover crops, mulching, and aiding the development of a weed cover; finally, seeding the area for permanent control.