602 PROTECTION AGAINST SWAMPS. 



a thorough inquiry should be made into all the bearings of 

 the question, as extensive drainage- works, especially in 

 mountainous districts, may damage a wide tract of coun- 

 try, and thus quite outweigh the advantages gained by 

 affording a larger area for forest-growth and an increased 

 yield of wood. Experience shows that by draining swamps 

 and moorland at high altitudes, the supply of moisture to 

 the soil and atmosphere may become so reduced that forest- 

 growth and agriculture suffer in districts lower down. This 

 calamity is especially liable to affect older deep-rooted woody 

 species, and woods accustomed to plenty of moisture in the 

 soil. Drainage causes subsidence of the soil, and thus the 

 roots of shallow-rooted trees such as spruce may become 

 exposed, while pedunculate oak and ash may become stag- 

 headed, owing to their roots being less supplied with moisture 

 than was formerly the case. Before, therefore, drainage is 

 attempted, the demands on moisture of the species growing or 

 to be grown on the drained area should be considered. 



Neighbouring lands may also be affected by the lowering of 

 the level of the underground water and drying up of the 

 surface-soil, which may have bad effects on field-crops. 



If the drainage of mountain forests be effected on a large 

 scale, the distribution of atmospheric precipitation may be 

 altered ; the drier air may hinder the condensation of watery 

 vapour, and the formation of dew and clouds may be lessened. 

 Instead of frequent gentle showers, irregular storms of rain 

 may come with disastrous results. 



A further disadvantage is the reduction of the quantity of 

 water in brooks and rivers, by which timber-floating, water- 

 carriage and works for utilising water-power may suffer 

 seriously. 



Keuss states that the harm done by ill-advised drainage is 

 most apparent in the Dobris mountain forests of the Colloredo- 

 Mansfeld family; through the extensive- drainage system, over 

 50 miles in length, effected there between 1858 and 1867, the 

 growth in forest and field fell off to such an extent that it 

 became necessary to fill up most of the drains. In the Harz 

 mountains also, in 1840, much harm was done by too exten- 

 sive drainage, whilst the attempts made since the middle of 



