MIXED CROP OP VARIOUS AGES. 89 



on the decline, allow them to shoot up without any impediment. 

 In other words, reproduction by seed, and to a less extent also by 

 coppice shoots, is singularly facihtated in a mixed forest composed 

 of individuals of various ages. 



VI. Individual ages. — Only one additional point under this 

 head need be noticed here. The presence of a variety of ages 

 gives weak species an excellent chince of resisting complete 

 baiishment from the crop, since some at least of its representatives, 

 of a sufficient age to have acquired the greatest tenacity of wliich 

 it is capable, are almost certain to have for neighbours either very 

 young or very aged individuals of the stronger associated species, 

 and to be thus able easily to hold their own.. 



VII. Relative longevity.— Greater longevity ceases to pos- 

 sess here the marked influence it exercises in a crop of uniform 

 age, for the longer-lived species must, at many points, be represent- 

 e 1 by old individuals on or near their decline and standing ovep 

 vis^orous younger stems of shorter-lived species which they are- 

 consequeutly powerless to suppress. If the differenca of ages is suffi- 

 ciently great, an extremely short-lived species will be able to occupy 

 a permanent place in a crop side by side with others capable of 

 living for centuries. 



VIII. Relative bapiditt of growth. — As said before, some 

 species have their period of rapid growth early in life, others later.. 

 Young individuals of the former class may hence outstrip older 

 trees of the other class and thus prevail in the end. But, on the- 

 other hand, these latter may be old enough to have entered upon 

 their phase of rapid growth, and then they may, in spite of dis- 

 advantages in other respects, maintain the start they originally had.. 

 As the relative ages of the trees of the several component species 

 of a crop would usually vary from point to point, the one result 

 might follow as often as the other, thus ensuring the permanence, 

 although it may be in very different pi-oportions, of all the species 

 in question. 



IX. Relative maximum height attainable. — ^Age can obvi- 

 ously exercise no influence on this Condition. 



X. Relative suitability of climate. — As under this Con- 

 dition we have considered only the influence which climate exercises 

 on the general growth of one species, taken in its entirety, as com- 

 pared with the similar influence it exercises on the general growth 

 of another, a difference of ages affects the remarks already made 

 under this head in the Third Case only to the extent that the constant 

 presence of large and, therefore, protection-affording individuals of 



