DIVISION OF FORESTKY. 189 



Tire been given; the advice having mostly been simply to mix, the 

 more the better. The variety of possible mixtures, with oiir rich forest 

 flora, enlarged by a few desirable foreign trees, is almost endless, but, 

 as outlined above, only a limited number will satisfy the requirements 

 of good forestry. With these requirements in view, after we have 

 determined what kinds are desirable and suitable to be planted in a 

 given locality, the possibility of mixing tv/o or more kinds depends — 



(a) On their relative capacity for preserving or increasing favora- 

 ble soil conditions; 



(b) On their relative dependence for development on light or 

 shade; and 



(c) On their relative rate of height growth. 



The densely foliaged and evergreen trees are best adapted to keep 

 the soil in proper condition. The first named are also capable of sus- 

 taining a considerable amount of shade without being appreciably 

 impeded in their development, while those with a thin foliage are 

 easily shaded out, often even by the moderate cover of their own kind, 

 though differences of soil, climate, &c. , modify this susceptibility. It is 

 their relative dependence on light, together with their relative rapid- 

 ity of height growth, which are most important for the determina- 

 tion of the kinds most suitable for mixtures. It is this difference 

 of requirement and development which accounts for the variety of 

 vegetation in a natural, especially a deciduous, forest, and for the 

 alternation of species so often observed in this country, when man, by 

 clearing, has altered the conditions of growth. The light-seeded, 

 quick-growing, light-needing aspens, maples, and birches are the 

 quickest to occupy the ground, until the shade-enduring and slower- 

 growing kinds have patiently struggled upwards, when they in their 

 turn crowa out the first occupants. 



The careful observations and measurements which are necessary 

 for a more satisfactory discussion of specific mixtures, and to which 

 mixtures our own forest flora is best adapted, have not been made, and 

 even notes from which deductions are possible are scarce, because 

 these relations of tree growth have seemingly never been pointed out 

 or understood in this country. 



We can at present, therefore, give only the general rules for mix- 

 ing which may be deduced from the foregoing remarks. 



Bute 1. — The dominant species, i. e., the one that occupies the 

 greater part of the ground, must be one that improves the soil condi- 

 tions, generally a shady kind. 



Rule 2. — Shade-enduring {i. e., densely foliaged) kinds may be 

 mixed together when the slower-growing kinds can be protected or 

 guarded against the overshading of the more raj^id grower, either by 

 planting the slower grower lirst or in greater numbers or in larger 

 specimens, or else by cutting back the quicker-growing ones. 



Eule 3. — Shade-enduring kinds may be mixed with light-needing 

 kinds when the latter are either quicker growing or are planted in 

 advance of the former or in larger specimens. 



Bule 4. — Thin-foliaged kinds should not be planted in mixtures by 

 themselves, except on very favorable soils, as in river bottoms, marshy 

 soil, &c. , where no exhaustion of soil humidity need be feared, or else 

 on very meager, dry soils, where most shady trees would refuse to 

 grow and one must make a virtue of necessity. 



Bule 5. — The mixing in of the light-foliaged trees in single indi- 

 viduals is preferable to placing them together in groups, unless special 



