A NATIONAL PLAN TOR AMERICAN FORESTRY 697 



that they require several more years to start height growth than do 

 the uninfected trees, and many of them die. Spraying with fungi- 

 cides during the first two or three years, and in some cases the use 

 of fire in preparing planting sites, are expected on the basis of studies 

 now in progress to minimize the losses from this disease at a cost 

 that would be more than counterbalanced by the decreased length 

 of time required for the establishment of the plantation; but with 

 the best success than can be expected this disease will continue to 

 be something of a handicap in the reforestation of the large areas 

 of denuded longleaf land in the South. Another disease of young 

 plantations which can be only partially avoided by any methods at 

 present known is the Phacidium blight of spruce and fir in the North- 

 east, which destroys trees that are small enough to be buried in 

 snow. 



Where sites are obviously not properly adapted to the species or 

 are chosen without reference to disease hazards, plantations may be 

 badly injured by disease in early life. For example, Douglas fir is 

 seriously damaged if planted where late spring frosts are frequent. 

 Conifer plantations should not be located on land where certain 

 parasites are present in quantity unless it first proves practicable to 

 destroy the sources of infection. This rule holds for the dwarf mistle- 

 toes of pine and Douglas fir in the West, and for stem rusts that easily 

 attack ponderosa pine, loblolly pine, and other species of both East 

 and West. In reforesting sites in parts of the industrial region of 

 the Northeast, species particularly susceptible to injury or growth 

 reduction by smoke or sulphur dioxide should not be employed. 



In general plantations continue healthy till they reach the sapling 

 or pole stage, but some of them begin to deteriorate after that time. 

 Even trees that are not overcrowded may stagnate, or become de- 

 formed, or perhaps die. Such failures in plantations that had started 

 well are little understood. Part of them appear to be due to root 

 diseases, which are enabled to attack the trees as the result of too 

 deep planting, unfavorable soil, the use of pure stands of a single 

 species, or the use of stock grown from seed collected in habitats 

 different from that in which the planting is made. All types of 

 parasitic disease, but especially the root rots, are favored by growing 

 large numbers of the same species of plant in pure stand. Pure 

 stands are relatively rare in nature, and their use in plantations 

 undoubtedly accounts for some of the disease liability. No one 

 knows enough about soil factors to be certain what sites will grow 

 healthy plantations of any particular species, and most plantations 

 are of necessity placed on old fields where soil conditions are no longer 

 normal for forest growth. There is particular need to correlate soil 

 studies with studies of plantation diseases. While root troubles are 

 difficult and expensive subjects for investigation, it is highly desir- 

 able that unsatisfactory plantations should be subjected to intensive 

 root study by pathologists. 



Most of our forest species have practically all of their finer absorb- 

 ing roots infected with mycorrhiza fungi, so that their absorption 

 of moisture and minerals from the soil must be through layers of 

 symbiotic fungi. Some students of the mycorrhiza have regarded 

 them as beneficial to the tree, while others consider them harmful. 

 There is every reason to believe that some of the species of mycorrhiza 

 fungi are harmful to particular tree species or under some kinds of 



