INCREASING THE YIELD. 33 



were required for the trees to fully mature, one-fifth of the forest, or 20 

 acres, would be mature and ready to be cut during this period of 10 years. 

 One-fifth, or 20 acres, would have been cut over during the preceding 10 

 years, and would have restocked in small seedlings ; 20 acres would bear a 

 stand with an average age of 15 years. The stand on 20 acres would have 

 an average age of 25 years ; while that on 20 acres would have an average 

 age of 35 years. At the same time that saw timber was being cut in the 

 mature stand, large poles would be removed in thinning the 35-year-old 

 tract ; small poles would be removed in thinning the 25-year-old stand, and 

 small saplings in thinning the 15-year-old stand. This would insure a 

 continuous supply of large timber as the areas of the different age-classes 

 matured. At the same time there is always an area in process of restock- 

 ing equal to that which is being cut over. In a large tract, each cove 

 might take the place of the 100-acre tract, and a suitable grouping of age 

 classed be obtained in it. 



In developing groups, they may vary in size from 100 feet square to 

 two or three acres in extent. Strips, which in a mountainous region 

 might be located up and down the slope, may be from three to five chains 

 wide, or as might often be advisable in the mountains, they might coin- 

 cide with the limits of narrow coves or hollows. On small tracts, such 

 as farm forests, blocks or cutting units which are designated with the 

 object of facilitating management, might be so small as to form in reality 

 a group selection form. 



Natural forests seldom occur in the forms which have been recom- 

 mended, but the tendency is for even-aged stands to result from clean 

 cutting. There is also a tendency in the mountainous portions of Ten- 

 nessee for the formation of even-aged second growth stands in the coves 

 and hollows, where these are cut clean and for the formation on the slopes 

 of even-aged groups or strips of young timber alternating with groups 

 or strips of old timber which were not felled, either because they were 

 less accessible or because they were largely composed of inferior species 

 or low-grade trees. In extensive operations, this last condition forms a 

 basis for ultimate conversion into a form of groups or strips which is 

 adapted to logging at frequent intervals. It is impossible to convert 

 from the present irregular form of stand without some slight cost; and 

 in the case of large and inaccessible tracts on which operating charges are 

 high, conversion must be affected gradually in order to reduce the cost. 

 A compromise, consequently, is necessary. The owner foregoes a 

 part of his present profit with the expectation of greatly increasing 

 the earning power of his land at the date when future cuttings 

 are made. A tree is left in one place which could be removed at a slight 

 present profit, but which is increasing in value at a high rate. Another tree 



