CONIFERS VS. CROP PLANTS AS BREEDING MATERIAL 23 



Changes in the technology of converting wood to useful products may 

 be large and sudden, with consequent sudden changes in the relative values 

 of the tree species composing a forest This obvious fact has led to the 

 argument that disease-threatened species are replaceable. The history 

 of American agriculture records several major shifts in crop production 

 caused, at least in part, by biotic enemies of crop plants. Nevertheless, 

 it may be fairly argued that the situation in forestry is different, at 

 least where an indigenous host species is involved. Most of our agricul- 

 tural crop plants are to some extent exotics. Their loss from cultivation 

 in a particular area is not an impoverishment of our biological endowment. 

 Our indigenous forest tree species are uniquely adapted to growth in 

 specific areas and some of them cannot be moved to escape their enemies. 

 There is only short-term monetary justification for allowing indigenous 

 species to become extinct or rare, one by one. 



White pine forests and forestry have distinctive characteristics, 

 mostly related to the fact that these forests are found almost exclusively 

 in mountainous or glaciated terrain. (Any of the world's white pines 

 could have aptly been named P. monticola.) Much of the area has numerous 

 micro-climates which are especially favorable to spread of white pine 

 blister rust, specifically the heavy fogs of early autumn when transmission 

 from ribes to pine occurs. The mountainous or glaciated terrain also tends 

 to accentuate the features of forest management noted above, namely 

 reliance on natural regeneration and the maintenance of mixed stands. The 

 white pine regions of North America are among our most scenic areas, either 

 as settings for lakes or as easels on which the forests are held up to 

 view. In either case, public scrutiny is intense and becoming more so. 

 As a serai or pioneer species, Pinus monticola Dougl. forms important 

 stands following the many and extensive fires which have occurred in 

 several of the broad habitat types delinated by Daubenmire and Daubenmire 

 (1968) in the northern Idaho--eastern Washington region. This habit is 

 shared by P. monticola elsewhere in the west, and Pinus strobus L. has 

 reached high levels of economic importance as a pioneer species following 

 fire and land abandonment on many types of habitat throughout its much 

 larger region in eastern North America. 



Aside from the occurrence of white pines over a very wide spectrum 

 of environments, we have evidence that, not surprisingly, local populations 

 have become adapted to local environments. How local these may be is 

 suggested by a study by Bingham and Squillace (1958) which showed evidence 

 of localized ecotypes adapted to differences in aspect and to environmental 

 variables found within a north Idaho area measuring less than 30 by 24 

 miles, but including white pine populations on sites ranging from 2700 to 

 5000 feet above sea level. Bingham and Squillace's evidence on aspect 

 races of a conifer growing in mountainous terrain has recently received 

 support from similar findings of Hermann and Lavender (1968) , who studied 

 aspect races of Douglas-fir in southwestern Oregon. These are simply two 

 of a number of studies which are revealing important clinal and ecotypic 

 variation in forest tree populations in mountainous regions. It is impor- 

 tant to note that many of the respects in which these ecotypes and clines 

 exhibit variation are revealed in growth and survival of seedlings--a 

 matter of obvious concern in the development of disease-resistant types 

 for planting. We have therefore not only a wealth of breeding materials, 

 but a plethora of environments requiring adapted resistant trees. 



These characteristics of white pine trees and forestry influence both 

 the strategy and tactics of resistance breeding. Another important influ- 

 ence is the nature of the host-parasite relationship, specifically the 



