65 



cies alternate with the trees of other species. On the other hand, 

 when the mixture is by groups, a number of trees of one species 

 forming a group alternate with groups of the other species. In 

 this case, each of the groups partake, to a greater or less extent, 

 of the character of a pure wood. The groups may be of definite 

 size and form or irregular in size and form to conform with irregu- 

 larities in the site. 



We may plan for the mixture to be permanent or only temporary 

 in character. We may also plan for all the species to be sown or 

 planted at the same time so as to result in an even-aged stand, or 

 at different times so as to result in an uneven-aged stand. 



7. Rules for the Formation of Mixed Crops 



Gayer 1 has formulated the silvicultural principles involved in 

 the formation of mixed crops as follows: 



a. The particular conditions of soil and situation must be such 

 as are favorable to the normal development of all species of trees 

 intended to be grown in mixtures. 



6. The mixture of species must not be such as ultimately en- 

 dangers the productive capacity of the soil. 



c. Each species must find the requisite amount of growing 

 space. It must have the light, air, and warmth suited to its re- 

 quirements throughout the entire period of rotation. 



Heyer 2 gives the following rules for the formation of mixed 

 stands : 



a. The ruling species must be capable of improving the soil. 



6. Tolerant species may be grown in mixture with each other 

 when the rate of growth is approximately the same or when the 

 slower-growing species is protected against the more rapidly 

 growing ones by planting or seeding it earlier, by having it form 

 a large percentage of the crop, or by lopping, topping, or other- 

 wise holding back the more rapidly growing species. 



c. Tolerant species may be intermixed with intolerant (thin- 

 foliaged) species when the latter are of more rapid growth in 

 height or when they are started earlier in the mixture. If, how- 

 ever, the tolerant species make more rapid height growth, they 

 must be the ruling species numerically. 



1 Gayer, Karl: Der Waldbau. 4. Aufl., S. 223. Berlin, 1898. 



2 Heyer, Carl: Der Waldbau oder die Forstproduktenzucht. 5. Aufl. I. Bd., 

 S. 37-54. Leipzig, 1906. 



