FOREST THINNING AND ITS RESULTS. 



BY 



WILLIAM F. HUBBARD, 



FIELD ASSISTANT, BUKEAT' OF FORESTRY. 



PART 1 1. --THE RESULT OF THINNING. 



THE Forest Academy at Tharandt 

 has one of the oldest and most 

 systematically carried out thinning ex- 

 periments in Germany.'-- The stand is 

 Scotch pine and belongs to the first- 

 quality class. This tract was taken 

 under observation in 1862, and since 

 1863 has received systematic thinnings 

 in five-year periods. Three grades have 

 been used A, B, and C. The A grade 

 only removes class \ 7 b, and may there- 

 fore hardly be called a thinning at all ; 

 but in B , classesV/', \a , and I V^> are taken , 

 and in C, besides these also class IV 

 and part of III. The table on the fol- 

 lowing page shows detailed results of 

 this experiment. 



The most noticeable fact in this table 

 is the comparative lack of result in the 

 B thinning. On the other hand, the C 

 shows a most pronounced increase in 

 quality and general character over the 

 unthinned area. With two hundred 

 trees less to the acre, the volume is the 

 same as that in the first plot, the aver- 

 age tree being more than an inch greater 

 in diameter and ten feet higher. This 

 means that the timber is of a higher 

 quality and will bring a much better 

 price. There has also been an interme- 

 diate yield of 1,036 cubic feet of sound 

 wood against 421 cubic feet of nearly 

 worthless dead wood in the unthinned 

 acre. It is also clear that the damage 

 from wind, insect 1 -, etc., decreases with 

 the degree of thinning, a direct answer 

 to those who claim that thinning endan- 

 gers the forest from windfall. 



An experiment quite similar to that 

 at Tharandt was instituted at the Aus- 

 trian station in Mariabrunn.r The first 

 thinnings were begun in 1882, and have 



* Kunzein Tharandter Forstl. Jahrbuch,vol. 

 45- pp. 1-44; vol. 52, p. 157. 



jCHster Forst. 6c Jagdt. Zeitung, May, 1903. 



been carried on in five-year periods to 

 the present. The species is Austrian 

 black pine (Finns lancio austriaca) , and 

 the thinnings are designated I, II, and 

 III, corresponding very closely to the 

 above given A, B, and C. A light in- 

 crement cutting is also included, desig- 

 nated by IV. This is out of the pale 

 of thinning, but incidentally shows a 

 poor result compared with III. The 

 accompanying plate, taken from a pho- 

 tograph, shows the diameter growth of 

 the average tree in each grade. The 

 increased growth of III over I is very 

 noticeable. On the other hand, II also 

 shows very well. 



As the result of a very greatly in- 

 creased interest in this subject, which 

 commenced about 1885, Prof. Buehler, 

 then head of the Swiss Forest Experi- 

 ment Station at Zurich,* began an elabo- 

 rate experiment in thinning where four 

 degrees were tested. These w 7 ere desig- 

 nated by A, B, C, and D, corresponding 

 to the table given in the preceding arti- 

 cle. A total number of 254 experimental 

 plots, averaging about an acre each, were 

 laid out in spruce, silver fir, and beech, 

 and all trials were rigorously carried out 

 by the same system. Since that time 

 other areas have been taken on, but, for 

 the sake of brevity, only the outcome of 

 a series of spruce thinnings in the Sihl- 

 wald wall be discussed. The table on 

 page 315 is a summary of the main re- 

 sults. 



In this experiment the degrees of thin- 

 ning differ slightly from those given in 

 the preceding table. The A thinning 

 approaches the B thinning at Tharandt, 

 the Swiss B thinning lies between the 

 German B and C, and the Swiss C 

 slightly exceeds the C at Tharandt. 



*Mitt. d. Sehw. Centralanstalt f. d. Forstl. 

 Versuchswesen, vol. 3, p. 7, and vol. vii, p. i. 



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