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THE FIXATION OF SAND DUNES
Picea alba are well spoken of for special purposes. The Alder (Alnus glutinosa) is invaluable, and compares with the Mountain Pine in resistance to extremes. It has been much employed to form belts immediately behind the littoral dunes, and in general on the lower, moister flats. It thrives in pure formations. The Birch (Betula verrucosa) is valuable for mixing with other trees, especially with Alders, to fill gaps and to occupy the drier marginal belts. It has a high power of natural rejuvenation from seed.
   In France, particularly on the long strip of coast from the Gironde to the Adour, marvellous results have followed the stabilizing of the dunes. The establishment of great forests here was started 130 years ago, largely at the instigation of Brémontier. The importance of both the littoral dune and the protective forest belt was appreciated at an early stage, whilst by planting largely the Pinaster or Maritime Pine (Pinus Pinaster), here well suited by the climatic conditions, a most valuable industry in the exploitation of this tree for turpentine and other products of the resin has been developed. Nor is this all, for the trees when they have yielded their resin furnish timber. The export of pit props to England alone is stated to reach 600,000 tons per annum.
   Considerable areas of wandering dunes have also been planted with Pines at Le Touquet, S. of Boulogne, but much remains to be done.
   In 1914 a project was investigated by the county anthorities for the construction of a high road to run from Rhyl eastwards, along the coast-line, and in rear of the sand dunes. Fig. 17 shows the scheme of tree plantation evolved for that portion of the road abutting on the edge of the landward sand slopes of the dunes.
   In Gascony the method of planting differs from that on the Baltic. The Pinaster seeds are mingled with those of Gorse, Genista, and Marram Grass, and as sown they are covered with faggots. The Marram and low bushes make excellent cover for nursing the Pines. Where the conditions permit it is obvious that sowing will be much less costly than planting.
   The United States of America, under their Department of