BRITISH FOREST TREES 225 



rivulets its growth is better than in fens, marshes, bogs, and 

 swamps. It can, however, stand an approach to wetness of 

 soil better than any tendency towards mere freshness in 

 the ground. A slight alteration in the amount of soil- 

 moisture, such as might be occasioned by the reduction of 

 the water-level owing to neighbouring drainage-works for 

 example, at once affects its development, and speedily leads 

 to the crowns becoming dry and dying off. 



With regard to the mineral constituency of the soil, the 

 alder is, taken all in all, by no means indifferent, or even 

 easily satisfied. Its best development is attained on humose 

 loam, or loamy sand, with an admixture of lime, or on 

 humose sand with loamy or marly subsoil. The less the 

 percentage of loam the poorer the subsoil, and the more the 

 tendency towards stagnation of soil-moisture with consequent 

 formation of humic and other similar acids owing to the 

 imperfect decomposition of dead vegetable matter, the less 

 suitable are marshy soils for the alder. Pure limes, and 

 pure sandy soils, are alike unfavourable to its growth. And 

 not every moist soil produces its fair growth of alder woods ; 

 cold clays, poor loam, peat-bogs, and salt alluvial deposits 

 along the coast with brackish soil-moisture, yield alike un- 

 satisfactory results. 



The alder is not particular as to aspect ; its preference 

 for northern and eastern exposures is to be attributed rather 

 to their greater relative humidity of atmosphere and generally 

 moister soil than to any conditions dependent on their low 

 degree of warmth. 



The yield of timber varies greatly according to the soil 

 and subsoil, the average annual increment ranging from 

 15 to 150 cubic feet per acre. The better classes of alder 

 soils are, however, as a rule such that they can easily be 

 drained to serve a higher economic purpose as gra/ing lands 

 and meadows. 



