34 BULLETIN" 604, U. S. DEPARTMENT OF AGRICULTURE. 



SPECIES IN MIXTURE. 



All things considered, yellow pine is probably the most desirable 

 tree to grow in combination with incense cedar, for, although its 

 growth is more rapid, its foliage is not so dense as to suppress the 

 cedar materially during the first 75 or 100 years, and in close stands 

 it aids materially in forcing height growth and in shading out the 

 lower limbs, thus insuring a reasonably clear length. Sugar pine, 

 owing to its more open crown, is probably not so well adapted to 

 this purpose as yellow pine, and the firs (both white and Douglas), 

 because of their rapid growth and denser foliage, would tend to 

 suppress the cedar and thus materially retard its growth. 



SILVICULTUKAE SYSTEMS. 



It is probable that some modification of the shelterwood or selec- 

 tion border cutting will give the best results, although to a large 

 extent this will have to be worked out by actual field tests. The 

 considerations leading to this conclusion are: (1) The fact that in- 

 cense cedar is an abundant seed producer, (2) that reproduction is 

 established readily under a high forest but not so readily under a 

 dense cover or in the open, (3) that in this way stands practically 

 even aged can eventually be secured. Strictly even-aged forests over 

 areas of any considerable extent can of course be secured only by 

 planting, but this is out of the question under present economic con- 

 ditions. A method of cutting, then, that will insure approximately 

 even-aged stands is desirable. 



On areas large enough in extent to be capable of producing a sus- 

 tained yield sufficient to warrant continuous operations or cuts at 

 frequent intervals, say, every 5 or 10 years, the selection border cut- 

 ting or a progressive thinning of successive strips would seem to be 

 most advisable. This system allows the gradual opening up of the 

 forest, thus insuring satisfactory stocking and progressively even- 

 aged stands. On small areas, to be cut over only at long intervals or 

 at the end of the rotation, a modification of the shelterwood system, 

 which would provide for an opening up of the stand by the removal 

 of the nurse trees and larger cedars at the time growth ordinarily 

 begins to fall off, probably would give the most satisfactory results. 

 The period of rapid development could thus be prolonged and the 

 establishment of a second crop as an understory assured. 



While the silvicultural systems named above are applicable in 

 general, the details necessarily will have to be worked out in each 

 particular case. A feature in favor of these methods, however, is 

 their flexibility, which not only makes possible such modifications 

 as are necessary to meet local conditions, but also such changes as 

 may be necessary to meet variations in the silvicultural condition of 

 the stand or fluctuations of the market. 



