PRINCIPLES WHICH GOVERN COMPOSITION OF STAND 67 



are more easily corrected where there is a mixture of species be- 

 cause the least suitable species can be removed in the earlier 

 thinnings. 



i. When the resulting stand must be considered from an esthetic 

 point of view, mixed restocking is desirable because of its increased 

 beauty. 



9. Even-aged Mixtures 



Even-aged mixtures are of great variety. In general, however, 

 they may be reduced to three: 



a. Sporadic, i.e., by single trees. 



b. Lines, i.e., by alternate rows. 



c. Groups, i.e., by clusters of trees. 



Mixing by single trees requires the greatest judgment in the 

 selection of the species for'the mixture. In general, the height 

 growth and reciprocal pruning effect must be similar if all species 

 are to do equally well. In practice, such mixtures are seldom 

 successful due to the great difficulty in selecting species which 

 behave in a similar manner in these two respects. The use of an 

 equal number of all the species uniformly distributed cannot be too 

 strongly condemned for even-aged mixtures. However, the intro- 

 duction sporadically of a limited number of trees of a valuable 

 species, such as tulip or ash, with the matrix species can often be 

 done to advantage. The dependent trees should not be closer 

 than at intervals of 20 or 30 feet. The species which forms the 

 bulk of the crop as a rule must not exceed the dependent species 

 in height growth, and, furthermore, it should be capable of pruning 

 the dependent species. The greater value of the dependent species 

 will usually more than compensate in money value for the less satis- 

 factory growth of the ruling species. It should be clearly appre- 

 ciated that the greater the number of species in the mixture, the 

 greater is the uncertainty of the ultimate result on any particular 

 site. The fact should also be emphasized that a mixture that may 

 prove valuable for one site may be a failure on another. The 

 forming of complex even-aged mixtures should be avoided. 



Mixing by lines is usually but little better than mixing by 

 single trees due to the same objections. The planting of mix- 

 tures by alternate rows, where it is expected that each will form 

 a part of the ultimate stand, is condemned. It is far safer to 

 plant each species in strips of three rows or more as each strip par- 



