DISCUSSION 



The Tsuga/Paahistima habitat type, within which each of the three study areas 

 occurred, is one o£ the most productive habitat types of the Northern Rocky Mountains. 

 It is also characterized by a broad representation of tree species. Where advance 

 seedlings or seed are present after timber harvests, or seed sources remain within 

 range, natural regeneration is customarily prompt and soon results in heavily over- 

 stocked young stands that may contain as many as seven or eight commercially important 

 coniferous species in significant numbers. 



In areas where reproduction has become established under partial cuttings, the 

 density of the residual overstory and the time until it is removed greatly affect 

 reproduction development. The growth of intolerant species such as western larch, 

 Douglas-fir, and western white pine is soon inhibited by as little shading as that cast 

 by a light shelterwood. Under heavily shaded conditions such as those in the check 

 plot area of the Lower Sands Creek study, suppression mortality rapidly reduces the 

 number of intolerant trees. Even the quite tolerant grand fir suffers severe attri- 

 tion, eventually reducing the diversity of tree species available for later selection of 

 management alternatives simply to western hemlock and, perhaps, western redcedar. It 

 is likely, also, that the high incidence of heartrot usually found in older stands of 

 these tolerant species may be associated with greater susceptibility to injury and 

 infection during the long period typically spent as very slow-growing subordinate trees. 



Where reproduction stands have developed in clearcuts or where they have been 

 given early release from partially cut overstories, cleaning operations made while the 

 stands are still less than 30 to 35 years of age offer the best opportunity for select- 

 ing desirable combinations and distributions of species. Postponing the reduction in 

 density to later years may again sacrifice much in the diversity of species that might 

 be featured in management. This was true in the Upper West Branch study check plots 

 where western larch and lodgepole pine strongly dominated the stand at 38 years of age. 

 Any attempt then to favor other species by precommercial thinnings would pose problems 

 of adequacy of release; and heavy cutting of the larch and lodgepole pine would mean 

 the loss of considerable past stand production that had been concentrated on those 

 larger trees. In addition, some species, such as western white pine, lose their ability 

 to respond quickly and vigorously when release from heavy competition is delayed much 

 beyond 30 years (Deitschman 1966) . 



12 



