16 BULLETIN 544, U. S. DEPARTMENT OF AGRICULTURE. 



terns, particularly those of the shallow-rooted species, spruce is much 

 less windfirm when growing in crowded or pure stands than when 

 growing in the open or in mixture with hardwoods. Thus the rela- 

 tive size and the form of the crown of spruce growing under different 

 conditions of density and association is an index of its comparative 



wmdfirmness. 



REPRODUCTION. 



SOIL, MOISTURE, AND LIGHT. 



Spruce finds its most favorable conditions for germination and sub- 

 sequent early growth on the moist forest floor under cover of the not 

 too dense stand of the selection forest. Here a suitable seedbed of 

 moss, dead wood, and needle litter is found, which, being protected 

 from exposure to the drying influences of sun and wind, affords suffi- 

 cient moisture for germination and early development. That spruce 

 appears to be selective hi its seedbed requirements, and that observ- 

 ers are in disagreement as to whether it does better on mineral soil 

 or on moss, dead wood, or duff, is largely because so much depends 

 upon the moisture conditions in the different materials. 



A plentiful supply of soil moisture is absolutely essential, not alone 

 at the time of germination but throughout the period when the young 

 plant is becoming established. This condition can be most readily 

 obtained, and with the minimum amount of free moisture in the form 

 of precipitation and seepage, under cover of the forest. That spruce 

 will germinate and continue to grow and thrive on mineral soil can 

 not be gainsaid, but only when such soil is protected from drying 

 influences and is plentifully supplied with a constant amount of avail- 

 able moisture at or very near the surface. The same applies to 

 to needle litter and old logs . 



Needle litter when under a pure stand of spruce, particularly dense, 

 unthinned, even-aged stands, is apt to accumulate much more rapidly 

 than it will disintegrate. The upper layer forms a loosely compact 

 mantle, which rapidly loses its surface moisture when exposed to 

 drying influences. In the early spring or late fall, when humid con- 

 ditions prevail, this mantle of needle litter contains sufficient moisture 

 to induce germination, but the young plants are soon after destroyed 

 by frost or drought. Furthermore, it is difficult for the young seed- 

 lings to extend then root systems through the litter to mineral soil. 

 In consequence, it is not suitable for a seedbed, and in fact, under 

 such circumstances, is a great detriment to reproduction. If no great 

 depth of such litter exists, so that the disintegrating humus layer is 

 practically at the surface, the seedbed is admirable, since the humus 

 is very retentive of moisture, and the vegetable mold full of nourish- 

 ment. Acid humus, however, is not suitable, for though it is most 

 common in supermoist situations it is physiologically dry. The same 

 general considerations that apply to needle- litter apply to a still 

 greater extent to the leaf litter from hardwoods, since, particularly 



