Crown Space of Western Yellozv Pine. 339 



by no means fully stocked. Their average density hovered around 

 two-tenths and was generally less. 



The last two sample plots of one acre each were studied more 

 intensively than the other plots. The acres of the crown's were 

 carefully measured and plotted on maps' where the irregularity 

 and broken character of the forest cover, which was of pure Yel- 

 low pine, is strikingly illustrated. Especially is this noticeable 

 in the one case, where many of the trees are so crowded together 

 as to be very much suppressed, while if distributed at regular in- 

 tervals over the plot, there would have been ample space and to 

 spare, for every tree to have reached its best development. Prob- 

 ably these clumps of mature trees are the survivors of a dense 

 thicket of seedlings such as are seen everywhere throughout 

 the Yellow pine forests. If root competition for water were 

 an especially important factor in keeping Yellow pine forest 

 as open as they are characteristically found, it does' not seem likely 

 that the species should be so often found crowded together in 



TABLE VI. 



A summary of two i-acre sample plots taken in stands of Western 

 Yellow pine in Oregon. 



TREE CLASS 



groups. Large spaces do not occur around single trees, as a 

 rule, but around groups of trees. It seems probable that the 

 crowding together of the species rather aflfords a measure of 

 protection by shading the ground and thus lessening evaporation. 

 When the trees grow into poles and veterans, the competition 

 for light is the factor which thins out their numbers more 

 especially than the competition for moisture. 



In the second case the stand is more uniform than in the first, 

 but the same grouping of the trees is still evident enough. In 

 the first case the average tree is 21 inches D. B. H., the volume, 



