170 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 
ground, but had decreased by about ro per cent. at the top end of 
the bole, while the increase in rate of growth in volume had been 
marked from about three to four years after the thinning, and 
was still rapidly increasing when the trees were thrown. Such 
an effect as to growth in girth had previously been noted by 
Professor Huffel, of Nancy, in 1893, and this experiment confirms 
his previous observations. The mean annual results of the 
measurements were as follows :— 
Mean Annual Rate of Growth in 
Diameter 
Ar ct fectup es nee as Tera 
Fs Inches. Inches. Cubic feet. 
Before thinning, . : Sarl eee 1060 0°315 
After thinning, : ‘ : | I*160 0°972 0°525 
‘Difference, ; : “h0'448))) ous +0°2 rer 
But the result of the thinning, as evidenced over the whole 
sample plot, was more remarkable than that on the mere in- 
dividual tree, the total increment in volume being greater in the 
thinned than in the unthinned part; the total increase in girth 
near the base being as large in the thinned as in the unthinned 
part, and the mean annual increase in girth per stem at 5} feet 
being just twice as large in the thinned part as in the unthinned 
portion. And the advantage thus gained is, of course, all the 
greater in the former case, because the trees left standing are 
the best of the crop, the weaklings being eliminated by the thin- 
ning ; and this concentration of increment on a smaller number 
of superior trees is one of the great benefits obtainable by thin- 
ning. The total mean annual increase per acre during the ten 
years was estimated to be as follows :— 
Aven Growing Stock Average Annual Incre- 
A (1892). ment (1892-1902). 
. 
: Cubic feet. Cubic feet. 
| Thinned, . 5460 171°64 
Unthinned, 7224 162°68 
