258 FORMATION OF MIXED WOODS. 



shade bearing species, or where the species are arranged in 

 separate groups. 



Another instance is the regeneration of silver 11 r and spruce 

 woods in the Black Forest. There silver lir is favoured during 

 the regeneration process, and if an insufficient number of 

 spruce plants has sprung up, it is afterwards increased by 

 planting. 



2. Formation of Mixed Woods oj Uneven Age. 



It has been shown that the preservation of the mixture is 

 difficult, when the trees ai-e of the same age, or nearl}- so, and 

 that it requires constant care and attention, lest one species 

 should be suppressed b}^ another and disappear. Such unre- 

 mitting attention cannot always be given, apart from the 

 expense which it involves. Endeavours have been made, 

 therefore, to devise a method of mixing species which is less 

 dependent on constant attention, and this has been found in 

 giving to the mixed species a greater difference of age. Such 

 an arrangement causes a considerable difference in the ages of 

 the component parts of the wood. Each of these requires to 

 be regenerated at its own time, so that the process of regenera- 

 tion is gone through several times in the course of one rotation, 

 one part of the wood being regenerated on each occasion. 



Many varieties of mixed woods of uneven age have been 

 evolved, each of which corresponds, more or less, with a 

 distinct sylvicultural system. Of these the following claim 

 attention : — 



(a.) The group and selection systems. 



{h.) High forest with standards. 



(o.) Two-storied high forest. 



{d.) Mixed coppice with standards. 



a. The Grovp and Seler/ion ,^f/s/ems. 

 Under the group system the regeneration of a wood extends 

 over a period ranging up to 40 and even 50 years. By first 

 regenerating the groups consisting of the threatened species, 



