REPRODUCTION OF WESTERN YELLOW PINE 277 



transition from black jack to yellow pine is almost imperceptible. The 

 rule in all sample-plot work in this region is to class a tree as black 

 jack until it is distinctly a yellow pine. Despite this precaution, it oc- 

 casionally happens that a tree classed as yellow pine 5 years ago is now 

 classed as black jack and vice versa. Trees are, however, continually 

 passing from the black-jack stage to the yellow-pine stage, and the 

 number which actually undergo this transition in a 5-year period may 

 be ver}^ appreciable. 



INCREASE IN NUMBER OE TREES 



Tables i and 2 show considerable variation in the four plots with 

 respect to number of trees, proportion of yellow pine and black jack, 

 and increase from 1909 to i()i4. There is, however, a general agree- 

 ment in the preponderance of black jack over yellow pine. With the 

 exception of plot 2, all show a slow rate of increase, plot 3 having an 

 actual decrease. 



The decrease in number of black jack as indicated for three of the 

 plots in Table i is accounted for largely by the transition from the 

 black-jack to the yellow-pine stage, while the increase in yellow-pine is 

 due entirely to this transition. Unless the black jacks which grow into 

 the 4-inch diameter class exceed in number those which pass into the 

 yellow-pine stage, the black jacks will show a net decrease. 



On all of the plots with the exception of Xo. 2 the low number of 

 trees per acre indicates exceedingly incomplete stocking. This condi- 

 tion is accentuated by the fact that the trees occur in groups. Refer- 

 ence to the map of an intensive plot which is fairly typical shows that 

 the space covered by the crown is approximately only one-fifth of the 

 total area. In virgin stands usually less than one-half the area is cov- 

 ered by the crowns. To bring about more complete stocking is one of 

 the problems of forest management. Here arises the question of what 

 may be considered a fully stocked stand in western yellow pine. It is 

 reasonable to believe that portions of the present open spaces are not 

 fully utilized, but whether they could ever be filled so as to establish a 

 continuous crown cover is uncertain. It is probable that the land, on 

 account of the low and poorly distributed })recipitation, would not sup- 

 port a continuous stand uniformly as dense as the present groups. This 

 opinion is based upon the observance that roots commonly extend far 

 beyond the crowns into adjoining openings. The present investiga- 

 tions should ultimatel\ throw considerable light on this question. 



