188 REPORT OP THE COMMISSIONER OF AGRICULTURE. 



dense foliage are the only ones whicli should be planted in forests ,l)y 

 themselves. Such are the beeches, catalpas, hornbeams, spruces, firs, 

 and hemlocks, and on some soils perhaps the white and yellow pines. 

 But the unmixed growth of larch can only result in ultimate failure, 

 unless soil conditions are unusually favorable, as the requirement of 

 the larch of a cool and moist soil is not aided by its thin foliage. The 

 practice of planting, unmixed, the thin-foliaged Scotch pines in the 

 northern plain of Germany is excusable only, but not commendable. 



The planting of ash on thin soils, and of walnut or oak, without 

 some dense-foliaged companion or underbrush, can result only in the 

 deterioration of the soil and the consequent diminished wood produc- 

 tion, as may be noticed in many groves on our prairies. Of the Cot- 

 tonwood plantations it is needless to assert that they present the de- 

 teriorating influences of a thin and constantly thinning foliage in an 

 aggravated manner, and that, but for some considerations other than 

 those of good forestry, their widespread use on the prairie, especially 

 in unmixed plantations, can only be deplored. Their only recom- 

 mendation is that they are easily produced, and fast growers ; but they 

 are short-lived, their wood inferior, and their effect on the soil disas- 

 trous. 



Mixed planting^ then, should, once for all, form the rule. The fol- 

 lowing reasons for mixing or grouping forest trees have been given, 

 VIZ : The objectionable uniformity of unmixed growths, the advantage 

 of a variety of material, dilferences in the food requirements of dif- 

 ferent species, and especially the difference of their root systems. But, 

 though some of these considerations are weighty, more cogent reasons 

 are, the greater ease with which the soil can be kept continually under 

 cover and its humidity preserved, and the protection from injuries 

 by wind, fire, fungi, and insects which is afforded in mixed growths. 

 This preservation of favorable soil conditions can be accomplished 

 in unmixed growths only by planting those species which preserve a 

 dense foliage and enrich the soil by an abundant leaf -mold ; but there 

 are only a few such species. 



_ Admissible in pure growths only are the thinly f oliaged evergreens, 

 like Scotch pine, under which a moss cover generally compensates for 

 the missing shade. As soon as grass appears, however, the deteriora- 

 tion of the soil has begun, and requires the correcting interference of 

 the forester. On deep and naturally moist soils of course the same 

 means for the preservation of soil humidity may not be necessary, and 

 less shady kinds, especially for short rotations, may be planted by 

 themselves; for, as stated before, in their youth all trees have a rather 

 dense foliage. The preference, however, must in all cases be given to 

 a mixed growth. The advantages of mixed growths have been more 

 fully described in my report on Western Tree Planting. 



The mixture may be started simultaneously, or other species may 

 be introduced later into the originally pure plantation; it may be with 

 plants of the same age or of different age and size, as, for instance, by 

 sowing under the planted rows. It may be a temporary or constant 

 mixture, accordingly as we remove one kind earlier than the other 

 or let all grow on. 



The advantages of mixtures have now and then been pointed out 

 before by writers on forestry in this country, as well as the reasons 

 for close planting, but neither the true and most important rationale 

 for such practice has been presented, nor, what is still more to be re- 

 gretted for practical application, has the rationale of a correct mixt- 



