252 



FORESTRY INVESTIGATIONS U. S. DEPARTMENT OF AGRICULTURE. 



to bring the stand to 3 feet apart; he thinned when fifteen years old, and carefully measured 

 contents when twenty years old. Although the plantation was stocked on poor soil, yet the 

 average annual accretion was found to be 2.43 cords (Austrian) per acre, a yield "which is 

 unexcelled." The writer adds that "if in such growths the number of trees is reduced in the 

 lit'teeuth to twentieth years to 280 trees per acre, the yield in sixty years might equal that 

 obtained in one hundred or one hundred and fifty years in the old manner." 



A plantation of Norway spruce, made with seed, was when thirty-three years old still so dense 

 that it was impenetrable; hardly any increase was noticeable and the trees were covered with 

 lichens. When thirty-five years old it was thinned, and again, when forty-two years old the 

 condition of the growth was such as to make a thinning appear desirable; between the two 

 thinnings, within seven years, the accretion had increased by ItiO per cent, or 27 per cent yearly 

 in the average, and the appearance of the trees had changed for the better. 



A coppice of tanbark oak was thinned when fifteen years old on half the area; when twenty 

 years old both parts were cut, and it was found that the thinned part yielded more wood and more 

 and better bark than the unthinned part, and yielded in money 14.5 per cent more, although no 

 higher price was asked for the better bark. 



An area of 12 acres was planted, one-half with 2-year-old pine seedlings from the forest, the 

 other half with seed. 



Three thinnings were made with the following yield of round firewood (cut to billet length 

 and over 2. : inches in diameter) and brushwood (less than 2.^ inches in diameter). 



The planted part yielded at the thinnings: 



The sowing was first thinned when 8 years old, yielding: 



In twenty-four years the total yield, inclusive of thinning, was: 



Cubic feet of 

 solid wood. 



Planted part '. 3,495 



Sowed part . 1,998 



In favor of planted part 1 ; 497 



Thinnings are usually made for the following purposes: 



(1) Improvement cuttings, to improve the composition of the forest and give advantage to the 

 better kinds. 



(2) Interlucations, to improve the form and hasten development of young timber. 



(3) Regeneration cuttings, to produce favorable conditions for seed formation and reproduc- 

 tion of the forest. 



(4) Accretion cuttings, to improve rate of diameter growth in older timber. 



Thinnings are to open the crown-cover, giving access to light and air, their object being to 

 accelerate decomposition of the litter and turn it into available plant food; to improve the form 

 and hasten the development of the remaining growth. The degree of thinning depends on soil, 

 species, and age, and is best determined as a proportion between the present growth and that 

 which is to remain with reference either to crown-cover, mass, or diameter. 



