I04 Forestry Quarterly 



two are incompatible. Some bare slopes in the spruce zone, how- 

 ever, have grown over with grass to an extent which may per- 

 manently prevent natural or even artificial regeneration. 



No brambles and few weeds are present. Brush occurs only 

 on warmer and lower slopes to any extent, out of the proper 

 range of the Engelmann Spruce. Here it may probably benefit 

 to some extent the young Limber Pine and Red Fir. A few 

 cases are at present found where Aspen (Populus tremuloides 

 Michx.) stands as nurse to the young coniferous seedlings. How- 

 ever, the bulk of the evidence points to the conclusion that this 

 species had little or no influence upon the generation of Engel- 

 mann Sprue and Limber Pine that is now in its ascendancy. To 

 be sure, where Aspen is present, it sprouts the first season after a 

 fire, and thus may shelter the tardier and more slowly growing 

 conifer. But if the dispersal of a crop of coniferous seed should 

 be delayed some years, the leaves and twigs of the Aspen may 

 cover the seedbed so well prepared by the fire to an extent that 

 prevents the contact of seed and mineral soil. And this may be 

 all that is needed to prevent regeneration. However, many 

 observations teach that good reproduction exists among Aspen, 

 and that just as good or usually better reproduction is found 

 where there is not a trace of Aspen. Also conversely, very 

 sparse or no reproduction occurs both where Aspen is present 

 and where absent. 



The density required for natural pruning in the Engelmann 

 Spruce is very great. Trees three or four inches in diameter, 15 

 to 20 feet high, and 40 years old, must usually stand not over 

 one foot apart in order to lose their branches up to three or four 

 feet from the base. A typical Red Fir stand of the same size 

 but younger, was noted, where the density was but one-half to 

 one-third as great, and the trees had pruned four to five feet 

 from the base. No stands of like thrift and density, but of 

 younger age, being found in either species, the age at which 

 pruning begins was not determinable. The density required for 

 this pruning of course checks the growth of the individual very 

 greatly. While in both species, under otherwise similar and 

 best conditions, a stand of minimun density ( i ) makes a height 

 growth of 100 per cent, a stand of maximum density (10) will 

 show a height growth of approximately 50 per cent only. If in 

 the former stand diameter also be represented by 100 per cent, 

 the latter will show but 20 to 25 per cent. 



