698 A NATIONAL PLAN FOR AMERICAN FORESTRY 



conditions, and that some of the plantation difficulties may be due 

 to them. The subject has been found by early investigators to be 

 one of extraordinary difficulty. Systematic studies have been under- 

 taken recently in this country, and it is hoped that some of the points 

 in question may be cleared up. There seems to be no hope of pre- 

 venting the development of mycorrhiza, even if it were proven desir- 

 able to do so. There is, however, a possibility that when our 

 knowledge of these fungus-root structures becomes more adequate 

 we can influence the success of a plantation by seeing that the right 

 species of mycorrhiza fungi get possession of its roots before the 

 trees leave the nursery. 



In this connection special mention should be made of the disease 

 situation resulting from the use of exotic tree species in forest planta- 

 tions. A considerable number of foreign trees are being tried in a 

 small way by our forest planters, and Scotch pine and Norway spruce 

 are grown to a considerable extent in the Northeast. Exotics can be 

 advantageously planted for special local wants; for example, to pro- 

 duce hardwoods on the Pacific coast, to produce chemicals, as tannin 

 or heptane, or to supply timber that is more resistant to termites 

 and decay than the local species. As native species are eliminated 

 by introduced diseases or insects, we will have increased need for 

 trial of exotics. One case of introduction of exotics to replace a lost 

 species has already appeared in the Asiatic chestnut species which 

 are being introduced in quantity in the hope of getting a satisfactory 

 replacement of the American chestnut; these, although resistant to 

 chestnut blight, are already being attacked by several of our native 

 fungi. It is true that in migrating to a new home, a tree species 

 sometimes escapes from parasites which have reduced its usefulness 

 in its native range, and makes better growth in the new habitat than 

 it did in the country of origin; but most exotics are not so fortunate. 

 An introduced tree is very likely to find in our rich fungous flora at 

 least one parasite to which it will lack resistance. Such a fungus 

 may be rare or geographically limited at first, and cause no serious 

 trouble to isolated test plantings; but if the exotic tree becomes 

 widely used, the troublesome fungus can multiply and extend, slowly 

 at first and with gradually increasing speed, till at the end of one or 

 two generations of extensive use of the new tree its early promise 

 may entirely disappear. This is exactly what happened to our 

 American white pine when it was used in Europe. It was adopted 

 by British and Continental tree planters with great initial success. 

 Rapid growth and high quality in early trials resulted in extensive 

 planting. Now, after half a century of additional experience, white 

 pine is being abandoned over a large part of the countries in which 

 it was once popular. The ultimate failure is entirely due to a rust 

 fungus, previously rare in Europe, which found a congenial host in 

 the introduced species and gradually became more widespread and 

 abundant till it became a controlling factor. Scotch pine, the exotic 

 which we have most employed in the United States, and which seemed 

 for the first few decades to be quite free from enemies, is now being 

 attacked to an alarming extent in Pennsylvania, New York, and New 

 Jersey by at least three diseases, the sweetfern rust, the Woodgate 

 rust, and the other of yet undetermined cause. 



As has been pointed out, much of the pathological condition of 

 plantings of native species in the past appears to be due to the use of 



