286 SYLVICULTURE IN THE TROPICS 



PT. IV 



outer dune which is being formed. A second row of 

 boards or a wattle-fence is also sometimes erected 

 between it and the outer dune, to prevent the sand 

 which has drifted through from spreading over the 

 dunes. As soon as this is done, the outer range of 

 sand-hills is covered with leafy branches, the butt-end 

 of which is stuck into the sand to windward, the leafy 

 end resting on the ground to leeward. This is done 

 to prevent the wind from overturning the branches 

 and scattering them. At the same time as the branches 

 are put down, seeds of sand-binding grasses, such as 

 Psamma arenaria, of broom, gorse, and of Pinus 

 maritima are dibbled into the ground. After some 

 time these begin to germinate and to hold the soil. 



Fig. 90. 



The Psamma has also the advantage of being- able to 







give out fresh roots from upper nodes as the sand 

 gathers and covers the lower part of its stem, and thus 

 it helps still more in holding it. 



In the meanwhile sand gathers against the row of 

 boards, and ultimately covers a great part of them. 

 They must then be drawn out far enough to offer a 

 fresh obstacle to the moving sand, and this goes on 

 until a new outer dune has been formed, which, in its 

 turn, can be taken in hand and afforested, the palings 

 being put in at its foot next to the sea. While it is 

 growing, the rows of dunes inland can also be afforested, 

 and after a time the work will be restricted to the 

 new rows of outer dunes which get formed on the 

 seaside. Fig. 90 illustrates the description given above. 



