SYLVICULTURE. 



A high rotation often leads to a pure forest, a short-lived 

 admixture being gradually pressed out. 



Abroad the forester is required to maintain the fertility and 

 productiveness of the soil. Since light-demanding species allow 

 the soil to be baked by the sun during the pole and tree stage 

 of the forest when grown purely, admixture of shade bearers under 

 such conditions is advisable, obtained, for instance, by underplanting 

 Yellow Pine with Beech, when Pine is 50 years old. 



B. Kinds of mixture. 



A mixture may be temporary or permanent; a mixture may 

 be even aged or uneven aged; the species may or may not differ 

 in height growth; the mixture may be composed of single indi- 

 viduals; of strips, rows, bunches, groups; or it may show an 

 irregular character. 



In the course of time the original character of the mixture 

 might be changed entirely by the forester or by nature. 



C. Advantages of mixtures. 



Mixed forests take advantage of differences of soil qualities; 

 the moisture-demanding species gradually claiming the dells and 

 more modest kinds obtaining preponderance on the dry plateaus 

 or spurs. 



A mixture may form a preventive against late frost. 



A mixture is better protected against damages by fire, insects, 

 fungi, storms, snow, etc. 



A mixture produces a better quality of humus '(Pine and Oak 

 humus is better than pure Oak humus or pure Pine humus). 



A mixture produces a larger quantity of timber for the above 

 reasons in addition to the fact that a mixture allows its com- 

 ponents to more fully utilize the productive factors of the air 

 as well as those of the soil through 



a. Difference of crown formation, crown levels, crown density. 



b. Difference in root system (tap and flat-rooters mixed). 



c. Difference in mineral and light requirements. 



A mixture also tends to produce cleaner timber certainly so 

 for the benefit of light demanders when placed in mixture with 

 shade bearers. 



For all these reasons a mixed forest may be said to produce a 

 larger and safer revenue than a pure forest. 



Valuable species might be raised beyond the limits of their 

 habitat in mixed forests. 



D. Objections to mixed forest. 



35 



