A NATIONAL PLAN FOR AMERICAN FORESTRY 699 



seed from distant sources and different climates, rendering the native 

 tree species essentially an exotic in the locality where it is planted. 

 For example, Norway pine from northern Minnesota seed cannot be 

 expected to be normally resistant to parasites if it is planted in the 

 Middle Atlantic States. A native tree may even be planted entirely 

 outside of the natural range of the species; for example, northern 

 white pine is planted in Ohio and Indiana where despite good initial 

 growth plantations have suffered severe losses from an obscure wilt 

 disease. This practice of use of seed from a distance is always likely 

 to be followed to a certain extent, because of the difficulties in ob- 

 taining seed of some species just when and where it is wanted, but is 

 fortunately becoming less common as the foresters recognize its danger. 

 Another factor must, however, be considered in estimates of disease 

 susceptibility of future plantations. Forest geneticists are beginning 

 to select particularly desirable types from our timber species and even 

 to breed them. In poplars planted for pulp, vegetatively propagated 

 varieties will probably be in common use in the not distant future. 

 This means that strains of fungi very specially adapted to the par- 

 ticular strain of the tree species that is being used will have an un- 

 precedented opportunity to spread. In a promising attempt begun 

 some years ago by a paper company to utilize fertile overflow land 

 in Ohio by growing the so-called " Norway poplar", a uniform fast- 

 growing variety, the tree had to be abandoned because of a branch 

 canker disease which overran the plantings after they had been under 

 way for a period long enough to let the specialized parasite multiply. 

 While the forest- tree breeder will select his types from those that 

 appear resistant to the more important diseases, it will be very diffi- 

 cult to insure resistance to all the species and strains of fungi con- 

 cerned, and this will be particularly true for the soil-inhabiting fungi. 

 We have some reason to fear that progress in forest genetics, if or 

 where it goes far enough to give us planted forests of selected strains, 

 may conceivably put our forest plantations into somewhat the same 

 condition of disease susceptibility that we already see in our orchards. 

 This is particularly likely unless study of diseases and development 

 of methods for testing resistance proceed more rapidly for the species 

 to which the geneticists give their attention. On the whole, more 

 trouble is expected from disease in plantations than in nurseries or 

 in young stands arising by natural regeneration. Because of its cost, 

 there is little chance for direct control of diseases in field plantings. 

 This means that we must not only learn to distinguish the different 

 diseases, but particularly for the root diseases we must know their 

 means of spread and their relation to soil conditions, stand density, 

 species mixture, kind of mycorrhiza, and every other factor through 

 which the activity of the parasite or the resistance of the host may 

 be indirectly influenced either in choosing plantation sites or in making 

 and managing the plantations. Unless the present information on 

 these subjects is rapidly increased, it is to be expected that there will 

 continue to be disappointing results in some of the new plantations 

 due to injury by native disease organisms. 



DISEASES AFFECTING IMMATURE FORESTS 



Forest stands throughout their life are subject to unfavorable 

 influences which reduce their productive capacity, either by a reduc- 

 tion in the rate of growth or by adverse changes in the density of 



