RECLAMATION OF SAND-DUNES.

New Zealand Journal of Agriculture, Volume XVIII, Issue 3, 20 March 1919, Page 148

RECLAMATION OF SAND-DUNES.

By

E. PHILLIPS TURNER,

Officer in Charge of Forestry Branch, Lands Department.

In the reclamation of sand-dunes it is essential that operations be started where the sand-drift has its source, which in the case of coastal dunes is high-water mark. The area under treatment should be fenced off from stock, and rabbits exterminated.

It is best not to plant trees until a protective littoral dune has been raised, or a belt along the coast planted with marram-grass.

THE LITTORAL DUNE.

In France the first operation is to build up a littoral dune or artificial bank or foredune immediately -behind high-water mark. This is done by erecting two parallel sand-catching fences 6 ft. or 7 ft. apart and some distance to the landward of water mark. This distance should be so selected that advantage can be taken of the highest parts of the .banks of sand that have accumulated naturally along the shore. If there is no kind of natural littoral dune the sand-catching fences will be continuous, but where the former already exists it should be utilized as much as possible, and the-sand-catching fences need be erected only in the' top ends of the hollows (on the seaward slope) in order to gather enough sand to fill them up to the level of the existing mounds. When the top ends of the hollows have been filled up another similar fence should be erected lower down on the seaward side of each hollow, repeating the work till the whole hollow is filled. An ideal foredune should have a height of from 30 ft. to 35 ft., , with a long easy slope to the seaward, and a steep slope to the landwax It should be as straight as the. coast-line will allow, and : the. slopes as uniform as possible. ‘ " . . • ■

When a foredune has been raised to the desired height it may then be planted with marram-grass. The seaward side of the foredune is always kept under marram ; and should the grass fail at any places or be blown out by storms the gaps made must be at once repaired and replanted.

SAND-CATCHING FENCES.

For their sand-catching fences the French use sawn pickets, which are driven into the sand and afterwards raised when they are nearly covered up. Where, however, there is an abundance of manuka in New -Zealand a cheaper fence can be made by using thin, manuka sticks about 4 ft. or 5 ft. long and inserting them firmly in the sand, leaving a space between each equal to the diameter of the stick. Another method is to use light manuka scrub and lace it between wires or thin rails fixed to posts. Care must be taken, however, not to have the scrub too dense, as if the wind cannot pass through it hollows will be blown out at its base and no accumulation of sand will take place. The object of the fences is not to stop the wind, but merely to so lessen its force that the sand it is carrying will be deposited on the lee side of the fence. fences are more effective than one, but where

two fences are made the one on the weather side may be more open ; they should be about 7 ft. apart. When the accumulation of sand has covered up these fences others should be erected on top of but a little to the windward of them.

PLANTING MARRAM.

Marram for transplanting should be obtained from plants that are not more than two years old. • A hole is made by simply pushing a spade into the sand and pressing it backwards and forwards until a wedge-shaped hole is made. A bunch of marram-stems is then inserted to a depth of about 8 in. and the hole filled up by pressure of the foot on the sand. There should be not fewer than five stems of marram in

a bunch, and each stem should have two rooted joints. Near the sea the bunches of marram should be planted not more than 2 ft. apart, but inland this - distance may be increased to 3 ft. Care must be taken not to have the marram in lines that are parallel with the direction of the prevailing wind. Plants should be exposed as little as possible before planting, and the’best time to plant is wet weather. Autumn, winter, and spring are the only seasons in which planting may be done. On sand with an even surface the bunches of marram may be planted by using a plough.

PLANTING OF TREES.

The planting of trees is done only on the landward side of the foredune, and in places where the sand is bare it must be previously planted with marram. The best trees for New Zealand coastal dunes are Pinus radiata (insignis), Cuprcssus macrocarp a, Pinus muricata, Pinus

Thunbergii, and Pinus clensifloni. If the complete afforestation of the dunes is aimed at, then the trees nearest the sea, for a breadth of. about 12 . chains, must always be left to serve as a protection-belt. Trees in this belt are planted from 2 ft. to 3 ft. apart, but farther inland the distance may be increased to 4 ft. or 6 ft. according to the habit of the tree to be planted. / In Belgium and Holland the erection of a foredune by means of sand-catching fences is not practised, But marram alone is relied on to hold ,the coastal sand. This method is cheaper than but not so efficacious as the French method. An article by Van Bissel, a translation of which is appended, gives a full description of the methods adopted in Holland. Of the trees he mentions, only Pinus maritima has been found successful in this country, but it is not so good as the trees, quoted in the previous paragraph. - ' . It is far the best plan for any one who wishes to reclaim by afforestation to establish a small nursery not far from the area to be planted, as the seedling trees will then be more able to withstand coastal conditions.

RECLAMATION BY LUPINS AND GRASS.

After the fixation A of the coastal belt by means of marram and trees an owner of sand-dunes may prefer to reclaim the balance of his land by the comparatively inexpensive method of establishing tree-lupins on the area. .Where there is a fair amount of native vegetation on the sand lupin-seed may be sown or lupin-seedlings planted in the autumn, but the safest plan is to scatter over the sand small branches of lupins bearing ripe pods. . The seeds will drop out, and after the seeds have germinated the young plants will be protected by the branches. After lupin has become established, prairie-grass, clovers, trefoils, danthonia, microlaena, and cocksfoot may be sown in patches where the lupin is thin or where cattle have broken it down. (Cattle must never be allowed on the protection-belt.)