Forest Renewal 



123 



branch of forestry called management 

 or regulation, which determines the 

 rate of growth and allowable cut so 

 that continuous production from a 

 single property is assured, provided the 

 renewal phases are properly handled 

 in harvesting. 



Such an all-aged forest is known as 

 a selection forest, and the harvest and 

 renewal method applicable to it as 

 the selection system. No particular 

 provision is needed for differences in 

 seeding characteristics of species, be- 

 cause many trees of seed-producing age 

 are always standing on an acre. Also 

 present are smaller trees ready to take 

 advantage of and fill in the high open- 

 ings created by the harvest of the large, 

 mature individuals or groups. Natural 

 renewal under the selection system 

 therefore is constantly under way and, 

 unlike some of the other systems, is not 

 limited to any particular period in the 

 life history of the forest. 



Too much emphasis cannot be 

 placed, however, on the greatest con- 

 trolling factor respecting the applica- 

 bility of the selection system : It works 

 well as a method of forest renewal only 

 where the chosen species are capable 

 of germination, survival, and satisfac- 

 tory development in the shade of a 

 productive stand of older and larger 

 trees. Some species native to the United 

 States that fall in this category are 

 sugar maple, beech, some of the firs 

 and spruces, and several more tolerant 

 hardwoods or broadleaved species. 



For species that will not thrive in 

 an intimate mixture of all ages and 

 sizes, methods aimed at eventual com- 

 plete removal of the mature crop must 

 be adopted. Although a number of such 

 methods have been developed, they all 

 have their origins in two broad, basic 

 systems; each has the ultimate objec- 

 tive of producing stands in which there 

 is relatively little variation in the age 

 of individual trees. 



ONE OF THE BASIC SYSTEMS COn- 



sists of a series of partial cuttings as the 

 stand approaches maturity and termi- 

 nates in a final cut that removes the 



last of the crop. Two or more cuttings 

 may be spaced over a period of 10 to 

 30 years, or more, if the situation is 

 particularly difficult. 



Early cuttings of the series have 

 several objectives. They harvest the 

 poorer trees that may not survive until 

 later cuts as well as improve the growth 

 rate of the better trees that are left. 

 They may also harvest trees suitable 

 for specific products that have an un- 

 usually good demand at the time. From 

 the viewpoint of forest renewal, how- 

 ever, they open the stand enough to 

 stimulate production of seed and pro- 

 vide light so that new seedlings may 

 start. Later cuttings continue the har- 

 vest features and gradually provide 

 more light and other conditions favor- 

 ing the continued establishment of the 

 new crop and its development. 



When a satisfactory stand of young 

 trees has become established, the final 

 cut of mature trees is made; it frees 

 the new crop of all competition with 

 the old. The number of cuttings, their 

 intensity, and the periods between the 

 cuttings vary widely with the species 

 and other conditions, but all these vari- 

 ations are covered in the shelterwood 

 system. In the partial-cutting stages, 

 it may closely resemble or even be 

 confused with the selection system. 

 Where such confusion exists, the for- 

 est manager must seek reorientation in 

 a knowledge of the basic requirements 

 of the species or the mixture of species 

 with which he is dealing. 



The shelterwood system is designed 

 to meet the requirements of species 

 that require partial shade during es- 

 tablishment and early life, or of those 

 that tolerate some shade but are poor 

 seed producers, or of those that are 

 heavy-seeded. Red pine is an outstand- 

 ing example of a species whose re- 

 quirements are met by this system. 

 Ponderosa pine, the southern pines, 

 and the less tolerant oaks (such as 

 black oak and scarlet oak) also seem 

 well adapted to renewal by the shelter- 

 wood system. 



This system has an important fea- 

 ture in the opportunity it provides for 



