BRITISH FOREST TREES 117 



necessary shelter, and then under the unnecessary shade of 

 the parent trees, the seedlings retain for twenty to thirty 

 years, and often more, the capacity of attaining a good 

 normal development when the standards are finally removed 

 in accordance with whatever conditions as to fall and clear- 

 ance are laid down by the working-plan. 



For the retention of soil-moisture, shade during the first 

 few years is indispensable, and during the youthful period 

 of growth a moderate amount of it is not injurious, 

 although of course the extent to which it may be borne 

 without injury depends in each case on the concrete 

 factors of soil and situation. 



Attainment of Maturity and Reproductive Capacity. 

 The silver fir attains in the Black Forest 1 an age of 300 to 

 400 years, and stems of 130 to 150 ft. in height, with a girth 

 of 13 to 1 8 ft. at breast-height, are frequently to be met with 

 in that district. The period of rotation is usually fixed at 

 about 1 20 years, and natural reproduction by seed is spread 

 over a term of twenty-five to thirty years, or even forty years, 

 in order to allow the standards to thicken in girth and rapidly 

 develop into valuable timber ; on the lower hills, where the 

 younger assortments of timber have a fairly good market, 

 periods^of rotation vary from 80 to no years, with reproduc. 

 tion extending over fifteen to twenty five years. Seed-pro- 

 duction on a scale sufficient to accomplish natural regen- 

 eration begins about the seventieth year, and whilst some 

 seed is expected on an average once every two years, a good 

 year may be looked for about every third year. Owing 

 probably to the oil in the seed, essential in its character and 

 therefore liable to be dissipated by evaporation, its reproduc- 

 tive power soon diminishes, and the quality is good when test 

 experiments show agenninative rapacity of 50 to 60 percent. 

 There are about 1 1,000 to 13,000 seeds in one pound, without 

 1 Gcrwig, Die Weisstanne tin SchwarzicaM, 1868, pp. 67 and 87. 



