124 



the control of competing brush. In 

 many localities, too heavy a cut in the 

 maturing forest creates conditions 

 favoring the invasion of shrubs or 

 other undesired plants, which may 

 offer such serious competition to seed- 

 lings of the desired species that they 

 can later be established only by expen- 

 sive artificial measures, such as the re- 

 moval of brush followed by planting. 

 In many areas where such a threat is 

 present, careful attention to the tim- 

 ing and intensity of cutting can con- 

 trol brush and favor establishment of 

 valuable tree species. 



THE OTHER BASIC SYSTEM is sub- 

 stantially a single cutting that removes 

 all or nearly all of the mature crop. It 

 is primarily a clear-cutting system, but 

 its use in forestry is accompanied by 

 the concept of small cutting areas so 

 located with reference to seed sources 

 that a plentiful supply of seed can be 

 promptly disseminated over the cut- 

 ting locality. The methods developed 

 under this system take many forms. 

 In shape, they conform more or less to 

 the clear-cut strips, blocks, wedges, or 

 spots. After new growth is established 

 in the clear-cut areas, another series of 

 cuttings in adjoining mature timber is 

 made. In the United States, where 

 much forest renewal must be accom- 

 plished in forests that have been un- 

 managed in the past, a single series of 

 cuttings may consist of a diverse pat- 

 tern of irregularly shaped areas on 

 which mature timber stood at the time 

 management was started. 



If renewal is to be prompt and ade- 

 quate, the size of such clear cuttings 

 must be held to a safe minimum. 

 That is usually smaller than many per- 

 sons suppose, and is dictated by the 

 effective seeding distance of the ad- 

 joining uncut timber. For many spe- 

 cies (like the southern pines) such a 

 distance is usually not more than 400 

 or 500 feet. For others (such as red 

 spruce or Douglas-fir) it may be three 

 or four times that distance. Winds 

 often carry seed for many miles, but 

 the distance over which enough seed 



Yearbook^ of Agriculture 1949 



will reach the ground to produce a sat- 

 isfactory stocking of young growth is 

 usually rather short. 



The location of cutting areas down- 

 wind from seed sources is sometimes 

 important. For species that shed an 

 entire seed crop in a few days or weeks, 

 a wise precaution is to locate cutting 

 strips at right angles to the direction of 

 prevailing winds during the time of 

 year when seed is shed. The location 

 of other types of clear-cut areas can be 

 similarly directed with reference to de- 

 sirable seed sources and prevailing 

 winds during the time of seed fall. 

 Mountainous terrain and its effect on 

 wind currents may be fully as impor- 

 tant as the direction of prevailing 

 winds, and local knowledge of these 

 characteristics of wind is useful. For 

 species that shed seed slowly in the fall 

 and winter months, the location of the 

 cutting areas with respect to wind cur- 

 rents is of less importance. The varia- 

 tions in wind direction over a long 

 period are enough to accomplish the 

 necessary dissemination. 



Of greater importance than wind is 

 the quantity of seed necessary to pro- 

 duce an established crop of seedlings. 

 The difference between the number of 

 seed reaching the ground and the num- 

 ber of resulting seedlings is tremendous. 

 The difference has not been measured 

 for all species and localities in the 

 United States, but study thus far indi- 

 cates that 200 to 400 seed reach the 

 ground for every seedling that becomes 

 successfully established. 



Satisfactory renewal, therefore, re- 

 quires that several hundred thousand 

 seed an acre reach the ground within 

 a few years after cutting. 



The reasons for this difference are 

 many. Forest-tree seed are important 

 as food for wild birds and animals and, 

 where heavy populations of wildlife 

 exist, all or most of a seed crop may be 

 consumed. Many seed fall on inhos- 

 pitable spots for germination, and 

 many seedlings succumb during their 

 first season to the competition of other 

 plants or adverse weather. The practi- 

 cal importance of this difference be- 



