FOREST ATION, WITH EXAMPLES 165 



(3) the development of forests tends to stop torrents; (4) the fall of 

 forests redoubles the violence of torrents and can even start them afresh." 



An interesting study^ that illustrates methods of reforestation is an 

 area in the basin of the Ubaye (see Fig. 14, a) which comprises some 46,661 

 acres, 18 per cent of which was natural forest, now bearing only 34 per 

 cent of a stand. The species growing naturally include larch, fir, spruce, 

 mountain pine, beech, oak, alder, and willow. The species introduced 

 artificially are Austrian pine, ash, locust, birch, green alder, and aspen. 

 Of the species growing naturally the larch is the most valuable and is 

 found at its optimum in the forest of St. Paul. Unfortunately the growth 

 of Austrian pine slows up and the needles turn yellow when 15 to 25 

 years of age. Prior to this the tree makes good growth. 



In this region the limit of stable soil is a slope of 45 per cent. Where 

 the slope is less than this the ground can be planted immediately, but 

 where it is more the ground must be first sodded before it can be planted 

 to tree growth. Where the slope is 60 per cent or more grassing cannot 

 be undertaken, for the instability of the soil is an absolute obstacle. In 

 this event it is necessary to construct artificial dams or to wait until the 

 accumulation of talus has abated. 



Two general methods have been used to grass over ground that has been 

 eroded — sowing forage seed and planting sod. The first method was 

 formerly used .over large areas in this region but is now limited to un- 

 stable soil. "Sainfoin" and "fenasse" (see p. 408) were used separately 

 or mixed in the proportion of three to one. The seed was sowed in small 

 trenches or in horizontal lines at variable distances apart. On an 

 average 18 pounds of seed (costing $9.65) was necessary to sow one acre 

 of eroded ground. The labor amounted to $6.75, making a total cost of 

 $16.40 per acre. But as a result of experience laying sod has proved to be 

 the best method. Large tufts of Clamagrostis argentea were cut from- 

 near-by grass land and planted in rows IJ to 3 feet apart, or in quincunx.' 

 The sod costs $3.83 a thousand. Still another method that is often used 

 to fix rapidly the slopes of mountains or ravines is to sow "bugrone 

 arbrisseau" or to propagate hippophae rhamnoide, or willows, by suckers. 



Sowing was formerly employed in reforestation, but to-day the pref- 

 erence is for planting. Cembric pine, larch, and mountain pine are sown 

 at high altitudes, provided the slope is not more than 30 per cent to 40 

 per cent and there is enough vegetation or rock to protect the young 

 seedlings against water and sun. Otherwise planting is considered 

 necessary. The seed is sown in the spring, at these high altitudes about 

 the end of May. Although the spring sowing is often burned out by the 

 sun, if the sowing is delayed too late the germination is retarded and the 



6 Etude sur lea Forlts et les Reboisements de la Vallde de I'Ubaye, par H. Vincent, 

 1909. 



