CONSERVATION AND MANAGEMENT OF FORESTS 341 



The Dutch elm disease results in a plugging of the water con- 

 ducting elements in the sapwood of elms, with resulting wilt and 

 death of leaves, branches, and finally the tree. It was introduced 

 from Europe ten years ago, and threatens the elm with a fate 

 similar to that of the chestnut. Wood rotting fungi, though not 

 causing a speedy death are responsible for great losses, especially 

 in over mature timber, or timber in which growth is rapidly 

 diminishing due to age. In such timber, the annual amount of 

 wood added by growth is generally offset by the loss of an equal 

 amount through decay caused by various wood rots. Thus there 

 is lost each year a large volume of wood in standing timber and 

 likewise in manufactured wooden products which are used in 

 environments favorable to decay. While usually not directly 

 responsible for death of forest trees, these organisms do cause a 

 mechanical weakening of trees which predisposes them to wind- 

 fall and breakage by snow and ice. 



Among LEAF DISEASES of couifcrous trees, the rusts are proba- 

 bly the most damaging. In addition to destroying the leaves, 

 rusts often spread to twigs, branches, stems, and fruit. The pines, 



» spruces, hemlocks, firs, cedars, and larches are all subject to leaf 

 diseases of this sort. Among deciduous trees, the tar spot of maple 

 and willow is one of the commonest diseases. It may be found 

 as well developed, black splotches often one-fourth inch in 

 diameter on leaves of maple and willow in late summer or fall, 

 just before the foliage is shed. 



Further discussion of diseases of forest trees, as well as those 

 of mans other important plants, will be found in Chapter 25, 

 which deals exclusively with plant diseases. 



Harvesting the Timber Crop 



As pointed out before, the time to make provision for natural 

 reproduction of the forest is at the harvesting of the timber crop, 

 technically referred to as logging. In former days logging was 

 carried out with the idea expressed in the old slogan "cut and 

 get out." Today, however, far-sighted lumbermen and timber 

 owners log their forests with care, and thus are spared the 

 expenses of paying taxes upon unproductive forest areas as well 



