BRITISH FOREST TREES 295 



water-courses. When once it has established itself, a good 

 growth of grass soon follows on stretches where only bare 

 stones were formerly to be seen ; and frequent coppicing in 

 such localities only strengthens its power of improving the 

 soil. On the Rhine, too, it and willows are generally the 

 first trees to assert themselves on fresh, stony soil, thus 

 gradually paving the way for soil-formation and subsequent 

 growth of grasses. 



Requirements as to Light. Both alders occupy an inter- 

 mediate position between the light-demanding and the 

 shade bearing species of forest trees. But the white alder on 

 the whole makes a lower demand for light and air than the 

 other, as is shown by its somewhat denser foliage, its better 

 growth in secluded dells lying at the base of hills and 

 favoured perhaps with but scant sunshine, or as underwood 

 below standards of birch, Scots pine, common alder, or even 

 occasionally the oak. On suitable soil it can thrive fairly 

 as coppice under standards casting only a moderate amount 

 of shade, though under such circumstances its reproductive 

 energy from the stool is apt to be prematurely weakened. 



Attainment of Maturity and Reproductive Capacity. The 

 white alder is seldom allowed to attain its normal maturity 

 as high timber forest, but under any circumstances its timber 

 is not so good as that of the common alder. Its chief use is 

 for filling blanks in plantations, and thus forcing young oak, 

 ash, maple, &c., to a more energetic growth in height ; it 

 can be coppiced twice or thrice under such circumstances 

 before the stools and roots lose their reproductive power. 

 In cool situations, where soil and atmosphere are both 

 humid, it can attain an age of forty to fifty years without 

 exhibiting signs of senile decay and over-maturity ; but in 

 drier or warmer localities it reaches its full maturity in 

 little over half that time, whilst not only its energy in growth, 

 and its timber production in cubic contents, but also its 



