FOREST TYPES IX CENTRAL ROCKY MOUNTAINS. 151 



be anticipated only by very light cutting, except of course in the 

 upper spruce zone where there are no subclimatic trees. 



In the lower part of the spruce zone, too heavy selection cutting is 

 almost certain to encourage Douglas fir seedlings where that is the 

 species next in order, and lodgepole in the region where this tree has 

 invaded the Douglas fir and lower spruce zones. 



Much of the lodgepole forest would be replaced by spruce, and 

 other portions by Douglas fir, if the lodgepole were left uncut or were 

 thinned very lightly. The heavier the cutting, the more certain it is 

 that lodgepole pine will continue to hold the ground. 



Nearly all of the Douglas fir forest of the central Rockies, if cut too 

 heavily, is subject to invasion by western yellow pine or the worthless 

 limber pine. However, on northerly exposures, there is much less 

 danger of this, and a heavy cutting under the shelter-wood plan ap- 

 pears most likely to give prompt and desirable results. 



As the less severe yellow-pine sites will in the natural sequence of 

 events go over to Douglas nr, there is no very evident reason why 

 Douglas fir seedlings should not continue to come in with the protec- 

 tion of their parents only, if it should seem desirable to remove the 

 yellow pines, provided only the stand is not too greatly opened. A 

 much more serious problem is presented in the lower portion of the yel- 

 low-pine type, where the stands are always so open as to permit the 

 formation of sod, and where any new opening may be quickly occu- 

 pied by the perennial grasses. Silvicultural caution demands that 

 cutting be done only when there is a seed crop. A favorable year fol- 

 lowing can of course never be guaranteed. Evidence in the Southwest 

 to the contrary notwithstanding, the writer is firmly convinced that 

 the perpetuation of the mountainous yellow-pine forest in this region 

 can best be insured by the burning of the brush in piles, a measure 

 which, as everyone knows, eliminates the grasses for a period of sev- 

 eral years and gives the pine seedlings at least an equal opportunity 

 with other vegetation. 



On the general subject of brush disposal this study appears to have 

 offered only one other suggestion. It is believed that, where spruce 

 forests grow on moderately steep to very steep slopes, both the nature 

 of the ground and the relative openness of the stand prevent exces- 

 sively heavy accumulations of needle litter, which, an attempt has 

 been made to show, may afford a very unfriendly seedbed. On such 

 slopes there is likely to be advanced reproduction, and burning of the 

 brush is neither called for nor desirable. On the contrary, on flats 

 which usually produce the most superb spruce forests, very serious 

 delay of reproduction is likely to result, even after heavy cutting, un- 

 less some spots are laid bare. Furthermore, the accumulation of litter 

 should by no means be added to. Here the burning of brush is dis- 

 tinctly called for. There is some evidence that this may also reduce 

 the percentage of alpine fir (Abies lasiocarpa) seedlings, which are 

 more vigorous than spruce seedlings and establish more certainly in 

 deep litter. 



LITERATURE CITED. 



(1) Baker, O. E., and Finch, V. C. 



1917. Geography of the World's Agriculture. U. S. Dept. of Agr., 

 Office of Farm Management. 



(2) Barnes, C. R. 



1902. The Significance of Transpiration. Science, n. s., v. 15, no, 

 377. (Abstract.) 



