REPRODUCTION OF WESTERN YELLOW PINE 291 



which will overcome the reproduction difficulty. It is almost a cer- 

 tainty that reproduction of western yellow pine will, regardless of sil- 

 viculture, continue indefinitely to be a problem in certain sections of the 

 Southwest. On rare occasions dense reproduction will spring up spon- 

 taneously, as it has done in the past, but when this happens it will be 

 due more to favorable climatic conditions than to silviculture. Given 

 a good seed crop, followed by suitable climatic conditions over a period 

 of 2 or 3 years, and seedlings will spring up in abundance. Efforts to 

 discover regularity in the occurrence of this combination have thus far 

 not been rewarded with success. The climatic phase of the problem is 

 complicated by the fact that favorable conditions over at least two con- 

 secutive years seem to be required. Just what the conditions are has 

 not been definitely ascertained, but it is quite certain that moisture 

 plays the leading role. Good seed crops are even more irregular than 

 rainfall. This is due partly to the fact that cones often fail to mature. 

 Whatever may be the explanation, it is a fact that such a thing as a 

 general seed crop over the yellow-pine type is a rare occurrence. 



If we wish to depend entirely upon the chance occurrence of large 

 seedling crops under the conditions above described, all the silviculture 

 that is needed for reproduction is to leave sufficient seed trees. There 

 is, however, another process by which a forest may be restocked. 

 Every two or three years a few seedlings succeed in establishing them- 

 selves. If these seedlings are protected, they will in the course of two 

 or three decades establish a stand which though uneven-aged and ir- 

 regular, is nevertheless better than nothing. This process, though slow, 

 is more certain than the first, and therefore it should be the mainstay 

 of our regeneration scheme. Here is where silviculture can be called 

 into service. In years of most adverse conditions it will be of little 

 avail, but in average years it will be more or less effective. If by 

 proper management reproduction can be increased by 25 per cent in a 

 given period, or the period recjuircd for complete reproduction short- 

 ned by 5 or 10 years, the result may be considered worth the eft'ort. 

 What the net result will be under a given set of conditions cannot be 

 easily predicted ; but one thing seems fairly certain : no matter what 

 silvicultural system is practiced, reproduction will come slowly unless 

 there should be a coincidence of unusually favorable natural conditions 

 such as appear to have occurred at irregular intervals in the past. 



In order to solve the reproduction problem, sample plot records must 

 be supplemented by fundamental studies to determine: (i) What are 

 the sj)ecific conditions required for reproduction? (2) How nearly are 



