SILVICULTURAL SYSTEMS 25 



serves of scattered trees is advisable. Neither this nor the 

 preceding system can be used with any other than hght-seeded 

 trees. The best number of seed trees to be left varies con- 

 siderably, but they should not be farther apart than their 

 heights, three to eight per acre. Often very limby or partially 

 decayed trees, so long as they are windfirm, may be left for this 

 purpose. They should have large crowns occupying at least 

 half the tree's height, since these bear the largest crops of seed, 

 while suppressed and spindling trees have very little seed. The 

 investment consequent on this method is less than that entailed 

 by the previous method, since less timber in the aggregate is 

 left. Wherever many or valuable trees are required as seed 

 trees some other system should be substituted. 



After reproduction has been estabhshed the seed trees are 

 usually removed. In some cases small groups of three to ten 

 or more seed trees are left standing together. This is done to 

 better prevent windfall. 



d. Reserving Thrifty Standards {Reserve Seed-tree Method). 



Under the two systems just described trees are left for seed 

 alone, hence inferior trees may be left. Under the reserve seed- 

 tree system trees are left for greater growth as well as for seed, 

 and only straight, thrifty specimens are reserved. The system 

 is well adapted to stands of moderate age where there are many 

 trees capable of continuing a thrifty growth for years, probably 

 for another rotation. If, for example, the rotation used in white 

 pine were seventy-five years, these reserves or standards might be 

 left over one rotation, until they were one hundred and fifty 

 years old, when they would be very valuable for special purposes, 

 as for derrick sticks, besides having served as seed trees. While 

 under the previous system less than a dozen trees per acre are 

 required for seeding, under this system from 15 to 25 reserves 

 per acre may be left. Naturally the reproduction is better on 

 this account. 



