152 A MANUAL OF FORESTRY. 



of the age classes. In some cases the wood may be, 

 if necessary, attacked in two or more places at the 

 same time. 



For the rest, little or no difference exists between 

 this and the compartment system, except that the area 

 under regeneration is less concentrated in the former. 



3. The Group System of Natural Regeneration under 

 Shelter- Woods. 



If a forest is naturally regenerated under the compart- 

 ment system it may happen that, after the seed cutting, 

 the area is not, or is only partially, stocked with a new 

 crop. A second seed year must then be awaited, and in 

 the meantime, the cover having been thinned, the soil 

 may suffer considerably under the additional admission 

 of light, so that it may not present a fit germinating 

 bed when the second seed year arrives. Extensive 

 working of the soil or artificial formation has then to 

 step in. With the view of reducing this calamity to a 

 minimum, foresters hit upon the idea of only taking in 

 hand certain limited groups, scattered over the compart- 

 ment, in the first place ; when these have been success- 

 fully regenerated, they proceed with a second set of 

 groups, and so on, until the whole compartment has 

 passed through the process of regeneration. So far the 

 system would after all only present a modification of 

 the compartment system ; in fact a division of each com- 

 partment into a series of minute sub- compartments 

 (Fig- 70). 



In practice, however, the system has been further 

 modified : certain groups, as before, are taken first 



