38 



BULLETIN" 285, U. S. DEPARTMENT OF AGRICULTURE. 



A practical modification of the selection system which has been 

 recommended for northern hardwood management involves a cutting 

 to a minimum diameter limit, which is not fixed but varies according 

 to the average size of the timber and is higher for preferred and lower 

 for inferior species. To make logging financially possible, the cutting 

 must be rather heavy and at rather long intervals. It is thus im- 

 possible to control the species in the reproduction by regulating the 

 light supply. On the other hand, this compromise is about the only 

 one by which a sustained periodic yield could be at once provided for. 



Under many conditions the selection group method is the best that 

 could be practiced. This is true particularly for stands containing 

 intolerant species, whose reproduction may be favored by removing 

 small groups of trees in the vicinity of the seed trees. Groups of in- 

 tolerant seedlings, already started, may be freed in this way. White 

 ash is a species well fitted for management by this method. 1 



Two important considerations in management are the material 

 which it is aimed to produce and the rotation necessary to produce it. 

 Under silviculture the volume growth per acre may be expected to be 

 much greater than the average in the virgin forest, equal at least, to 

 the maximum shown in Tables 7 to 9. To ascertain what might be 

 expected of beech under management, the most rapid diameter- 

 growth rates for each one-half inch in radius of the beech trees on 

 which the growth values in Tables 7 to 9 are based were selected and 

 averaged by a curve. 2 The resulting " selective" growth rate, with 

 the per cent by which it exceeds the maximum, is shown in Table 13. 



Table 13. — Selective maximum diameter growth of Michigan beech. 



Age. 



Diameter breast-high. 



Age. 



Diameter breast-high. 



Composite 

 of maxi- 

 mum 

 decades. 



Excess over 

 maximum 



in Table 7. 



Composite 

 of maxi- 

 mum 

 decades. 



Excess over 

 maximum 

 in Table 7. 



Y'ears. 



10 



20 



30 



40 



50 



60 



Inches. 

 0.5 

 1.9 



3.8 

 5.9 



8.3 

 10.7 



Per cent. 



Y'ears. 



70 



80 



90 



100 



110 



Inches. 

 13.1 

 15.2 

 17.3 

 19.1 

 20.8 



Percent. 

 102 

 103 



101 

 99 

 92 



46 

 65 

 79 

 89 

 98 



Somewhat similar results are obtainable for other species. Trees 

 in the open undoubtedly grow even faster than this, but it is at the 

 expense of the long, clear log lengths of forest-grown trees. This 

 accelerated growth represents an ideal to be approached under man- 

 agement in which each tree would receive frord youth up just the 



1 See Department of Agriculture Bulletin 299. "The ashes: Their characteristics and management," 

 by W. D. Sterrett. 



2 This process was devised and applied by W. B. Barrows. 



