﻿40 



BULLETIN 24, U. S. DEPARTMENT OE AGRICULTURE. 



area the stand had been opened up too severely, and toward the cen- 

 ter many of the dominant trees appeared to have been taken along 

 with the smaller ones. One half-acre plot was laid off, however, 

 in which there was a fairly even distribution of the remaining trees, 

 and from which the smaller or medium-sized trees were the ones 

 chiefl} T removed. It happened that this small area was properly 

 thinned. Table 7 shows the condition in this half-acre plot in con- 

 trast to the average for stands of this age. 



Table 7. — Effect of thinning on cottonwood stands. 



Total 



number of 



trees per 



acre. 



Trees per 

 acre over 

 14 inches 

 diameter, 

 breasthigh. 



Average 

 diameter 

 of all trees. 



Average 



diameter of 



trees above 



14 inches 



diameter, 



breasthigh. 



Stand per 

 acre. 



Average plot. . 

 Thinned plot. 



215 

 132 



Inches. 

 10.5 

 12.3 



Inches. 

 15.5 

 15.9 



Board feet. 

 4,000 

 7,500 



In the thinned plot there were approximately 40 per cent fewer 

 trees per acre than in the average plot. Of trees over 14 inches in 

 diameter, on the other hand, there were actually 47 per cent more, 

 and the average diameter of all trees was 17 per cent larger in the 

 thinned than in the average plot. 



The results in this one thinned stand are corroborated by measure- 

 ments of five 15 -year- old plots of cotton wood across the river from 

 Helena, Ark., in which was an understory of sycamore and a few 

 other species, all more tolerant than cottonwood, and of the same 

 age as the latter though only one-third the height. It was therefore 

 apparent that the cottonwood started in mixture with the sycamore, 

 but being of more rapid growth soon overtopped it, thereby freeing 

 itself from crowding and side shade. Thus, while not actually 

 thinned, it had passed through a natural stage in some respects 

 closely paralleling artifical thinning. In these five plots the board- 

 foot yield noticeably exceeds the average for the same age stands. 



Table 8. — Effect of associate species on form, growth, and yield of cottonwood. 



Age 15 years. 



Average of all plots 



Average of 5 plots with sycamore under- 

 story 



Total 



number of 



of trees 



per acre. 



275 

 200 



Number 

 of trees 



per acre 

 over 14 

 inches 



diameter 

 breasthigh. 



22 

 27.6 



Average 

 diameter 

 of all trees. 



Inches. 

 9.2 



10.4 



Average 

 diameter 

 trees over 

 12 inches 

 diameter, 

 breast- 

 high. 



Inches. 

 14.9 



Yield per 

 acre. 



Board feet. 

 ' 2,400 



.3,040 



