STORMS. 547 



Fellings in high forest follow one another from east or 

 north-east to west or south-west, according as a compartment 

 is cleared in several years, or in one year. 



Figs. 249 and 250 show the arrangement of the age-classes 

 in a forest at Sternberg, in Thuringia. If it is wished to fell 

 the 70-year-old wood without endangering that 50 years old, 

 which it at present shelters from the west wind, it becomes 

 necessary to separate the two woods by a severance- felling. 

 This, as the diagrams show, has been already done six years 

 ago, when the strip was planted with -i-years-old spruce trans- 

 plants, which now form a lO-year^old protection belt to the 

 50-year-old trees. The westerly border-trees of the latter, 

 have now become so wind-firm that the severance-felling (/>) 

 might be widened. Another severance-felling (a) has also 

 been made between the 30 and 50-years-old woods, because 

 the latter is to the west of the former and will first be mature. 

 The proposed widening of (a) is marked in Fig. 249 by a line, 

 and in Fig. 250 by shading, but it cannot be carried out until 

 the younger wood has become more wind-firm. 



There is no apparent necessity for the severance-felling (<■), 

 as the woods on both sides of it are of the same age, but it 

 has been cut, in order that the large 50-years-old wood may 

 be divided into two cutting series, both beginning from the east 

 in order to avoid the necessity of having too large felling-areas. 



Indispensable severance-fellings, such as a and b, are 

 termed protective, whilst those like c, made for administrative 

 reasons, are termed silvicultural. 



Fig. 251 represents a normal arrangement of age-classes in 

 a forest,* the periodic blocks being variously shaded, and the 

 compartments drawn square instead of oblong, so as to take 

 up less room. The white compartments are the youngest, 

 forming the woods of the fifth period, and the darkest compart- 

 ments are those of the first period, where fellings will be at 

 once commenced. The intermediate shades represent the 

 second, third, and fourth periodic blocks. 



* A period is an integral part of a rotation, and a periodic block is the area of 

 forest which will be felled during any periotl. Thus a rotation of 100 years 

 may be divided into '> periods of 20 years each, and a working-section of a 

 forest into five periodic blocks, the trees in which are aged respectively — 20, 

 21—40, 41—60, 61-80, and 81—100 years. 



N N 2 . 



