74 BULLETIN 1105, U. S. DEPARTMENT OF AGRICULTURE. 



which are known to have occurred on these plots since 1909 have 

 yielded but few seedlings, because they were followed by deficient 

 rainfall. In 1919 copious rains throughout the summer would have 

 insured reproduction had a good supply of seed been present. 

 Through failure of the seed crop in this locality in 1918, moisture 

 conditions such as are not likely to occur again in 20 years were 

 rendered futile. Without an abundance of rain in July and August, 

 reproduction will fail on these plots, regardless of the number of 

 seed trees. A large number of seed trees should be left, however, 

 so that whenever a good seed crop and required moisture conditions 

 do coincide, there will be sufficient seed to secure complete restocking. 



Group V again proves the inadequacy of a small number of seed 

 trees such as are left on "timber rights" sections. 



Group VII indicates what may be expected on present-day Forest 

 Service cuttings with abundant rainfall but only an average " good " 

 seed crop. Had the seed crop been as heavy on this area as in 

 Groups I and II, it is safe to say that the number of seedlings would 

 have been increased threefold. Since this group involves three 

 methods of cutting, it will be discussed in greater detail under the 

 next caption. 



Comparison of methods of cutting. — Group VII provides a com- 

 parison between silvicultural systems without going to such extremes 

 as are encountered in comparing Forest Service cuttings with " tim- 

 ber rights" areas. In other words, the test in Group VII is con- 

 fined to methods which have silvicultural possibilities. An area 

 was cut according to each of the following methods : 



(1) Group selection. — This method, with minor modifications, has 

 been the standard of the Forest Service in the Southwestern district 

 for 15 years. It may be briefly characterized as a selection system 

 in which even-age tree groups are treated as individual trees. 

 Mature and overmature groups (yellow pine) are removed unless 

 needed for seed production or shelter; immature groups (blackjack 

 and intermediate trees) are left, unless they are diseased or de- 

 fective or unless improvement cuttings can be advantageously made. 

 It is desirable to preserve the natural groupings, because the dis- 

 integration of groups increases windfall. Trees which have grown 

 in an isolated position are most desirable to leave, but usually they 

 are too few. The application of this system is outlined in detail 

 at the end of this chapter. In present practice, from 75 to 80 

 per cent of the stand is removed, leaving 1,500 to 2,000 feet b. m. 

 in trees over 11 inches diameter breast high. These cuttings are 

 considerably heavier than those of 10 years ago, when the amount 

 left ran from 2,500 to 3,500 feet b. m. 



(2) Scattered seed-tree method. — Scattered trees were left at the 

 rate of from 3 to 4 per acre. Aside from the trees left for seed, 



