TREE PLANTING
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ties. Thus near Port Elizabeth, South Africa, troublesome dunes, exceeding 5000 acres in area, have been rendered dormant by strewing them with city refuse, and then planting with two species of Acacia (A. cyclopis and A. saligna), mingled with an indigenous grass (Ehrharta gigantea).
   Formerly wandering dunes were first netted over with Psamma squares as a preliminary to afforestation, but this practice has largely given place to the use of dead cover. Only when Psamma is available in superabundance, or the management favours adhesion to the traditional routine, does the method persist.
   The next act is the improvement of the soil and the planting of seedling trees. For manure, what is most available is taken —loam, peat, organic soil from the salt marsh, mud dredgings from the harbour, &c. These have to be stored long enough to mature lest the seedlings be injured. The seedling trees, raised in special nurseries, are planted out in their second year, one per square metre. Thus a square with 4-metre sides would receive sixteen young trees.
   In the selection of the species of trees, the primary consideration is to raise a covering that shall permanently hold the wandering sand. In North Germany, where the dread of the great white mountains of the eighteenth century still holds sway, the dune forests are regarded as protective belts, and their products are not exploited in any way except for materials to fix other dunes. The following are the trees which have been most extensively utilized, a selection based solely on their fitness for the special conditions. That is to say, these trees thrive best on the ground, and successfully resist the wind. They are not sensitive to sudden changes of temperature, they form a permanent canopy, and by the fall of their leaves continually improve the soil. Authorities place first the Mountain Pine (Pinus montana v. uncinata), from its high powers of resisting the most extreme conditions of wind, sea exposure, and dryness of soil. Moreover, its crown spreads laterally at an early stage and shelters the ground.
   Pinus sylvestris grows well, but is really suitable for the less exposed positions only. The Spruce (Picea excelsa) and
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