Breeding and Selecting Pest-Resistant Trees 



465 



eliminating fire, reducing felling and 

 skidding injuries, favoring low-origin 

 sprouts in hardwood cleanings, cut- 

 ting defective trees in partial-cutting 

 operations, controlling dwarf mistle- 

 toe, and by making prompt salvage in 

 stands that have been heavily dam- 

 aged by fire, wind, or ice. 



By maintaining suitable density in 

 stands until the lower tree trunks are 

 cleared of branches, or by artificial 

 pruning in the more open stands, the 

 incidence of heart rot attacks that de- 

 velop through dead branches and 

 branch stubs can be considerably re- 

 duced in young stands of a number of 

 important western conifers. Defects 

 can also be reduced in eastern white 

 pine and scarlet oak by early pruning. 



In eastern and southern softwoods, 

 a cutting age up to 80 years will avoid 

 serious rot losses unless the stands are 

 badly damaged. If fire-scarred pines or 

 otherwise defective pines are removed 

 during partial cuts, even longer rota- 

 tions would be fairly safe from the 

 decay standpoint for this group. In 

 most eastern hardwoods that are not 

 stump sprouts, cutting ages can be 

 raised to more than 100 years with lit- 

 tle loss from decay where the stands 

 are undamaged. Many of the western 

 conifers can be grown to even greater 

 ages without serious decay. 



The heart rots that develop through 

 the roots, as in the case of many of 

 the spruce, fir, and pine butt rots, will 

 never be entirely eliminated. Where 

 they are known to be common in a 

 stand, however, cutting can be done 

 early enough to minimize the loss, and 

 in such a way that the residual stand 

 will not suffer undue breakage or 

 windthrow as a result of the decay. 



GEORGE H. HEPTING, senior pathol- 

 ogist of the Division of Forest Pathol- 

 ogy, Bureau of Plant Industry, Soils, 

 and Agricultural Engineering, has 

 been engaged in the study of diseases 

 of forest and shade trees and forest 

 products for more than 20 years. He 

 has been stationed from time to time in 

 the Northeast, the Middle Atlantic 

 States, and the Deep South, and is now 

 in charge of the work of his Division 

 in the Southeast, with headquarters 

 at Asheville, N. C. 



JAMES W. KIMMEY, pathologist in 

 the same Division, has for the past 20 

 years conducted research in forest 

 pathology in the West. His territory 

 has included the entire area west of 

 the Rocky Mountains, and some in- 

 vestigations have taken him into west- 

 ern Canada as well. Dr. Kimmey is a 

 graduate in forestry of Oregon State 

 College and Yale University. 



BREEDING AND SELECTING PEST-RESISTANT TREES 



RUSSELL B. CLAPPER, JOHN M. MILLER 



Genetics has given us a good new 

 tool to use against the diseases and in- 

 sects of trees the selection and breed- 

 ing of trees for resistance to pests. It 

 is a long job. The time that a tree crop 

 takes to produce seed and to mature 

 exceeds the span of a human genera- 

 tion. Natural forces, aided now and 

 then by man, have determined through 

 the ages which forest species should 

 survive, and these are the species with 

 which the forester, the geneticist, and 

 the forest pathologist now work. 



Epidemics of introduced parasitic 

 fungi stimulated interest in the devel- 

 opment of healthier trees. Forty years 

 ago the Department of Agriculture em- 

 ployed Walter Van Fleet to breed 

 chestnut trees that would resist the 

 introduced blight fungus. Since then 

 several agencies have taken up the 

 work of breeding and selection, for the 

 most part to obtain vigorous, fast- 

 growing specimens for lumber and 

 other products. More recently, greater 

 emphasis has been placed on develop- 



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