4 BULLETIN 1105, U. S. DEPARTMENT OF AGRICULTURE. 



become established only at long and irregular intervals, when a good 

 seed crop is followed by two or more years of favorable climatic con- 

 ditions. More dependable results can be secured by the slower proc- 

 ess, in which a few seedlings are established every two or three years 

 under average conditions of seed and moisture. On average sites, a 

 sufficient number of seedlings will accumulate in two or three decades 

 to establish a fairly good stand. It was believed that although 

 silviculture could not hope to overcome the effects of adverse cli- 

 matic conditions, it might ameliorate them by taking advantage of 

 the protection afforded by standing trees, brush, and ground cover. 

 Root competition had not been extensively studied at that time. 

 Sheep were known to do serious damage to seedlings, but it had not 

 been proved that the damage was sufficient to preclude reproduc- 

 tion ; moreover, it was surmised that certain adverse sites, especially 

 bunch-grass lands, would not restock with any degree of certainty 

 even if sheep were excluded. What was needed to test the correct- 

 ness of th,e above deductions was a concrete demonstration of results. 

 No opportunity had been afforded for such a test. Thus, after the 

 study had been carrier on for nine years, many of the conclusions 

 were still open to question. 



RECENT DEVELOPMENTS IN THE STUDY. 



The year 1919 was an epoch-making one in the study of western 

 yellow pine reproduction. Developments on a number of sample 

 plots established in 1909 reached a point where it was possible to 

 show distinct progress, and to prove by actual results that the cumu- 

 lative process referred to above is effective. This development was 

 anticipated, but the unforseen also happened. In 1918 the seed crop 

 of western yellow pine over the entire Colorado Plateau was un- 

 usually abundant, and the summer rainfall in 1919 was the heaviest 

 recorded in years. The result was a seedling crop which, consider- 

 ing area covered as well as density, has not been equaled during the 

 25 years in which the forests in this region have been under 

 Forest Service administration. Thus we have in a single year a cor- 

 roboration of both theories previously advanced in regard to the proc- 

 ess of natural reproduction. Moreover, the abundance of seedlings 

 presents an opportunity for a study of the factors influencing their 

 establishment in a way which was not possible before. 



Most of the intensive studies have been made on the permanent 

 sample plots previously mentioned. There are 29 of these plots on 

 the Coconino and Tusayan National Forests. The area per plot 

 ranges from 2 to 12 acres and their aggregate area is 120 acres. Each 

 plot is mapped on a scale of 1 inch to the chain. The location of 

 every tree above 4 inches in diameter, scattered saplings and groups 

 of saplings below that diameter, logs, brush piles, and other features 



