While these gross comparisons favor spring over fall planting, the averages for 

 the two seasons can be misleading. Wide variation in survival percentages occurred 

 within the fall planting season. Survival from some fall plantings exceeded average 

 survival from spring planting. Notable were survival percentages for early fall-planted 

 spruce and late fall-planted larch, both of which exceeded the average survival result- 

 ing from spring planting by wide and fairly consistent margins. This wide variability 

 of survival results within the fall planting season suggests that much of the perform- 

 ance of fall-planted trees depends upon their physiological condition at time of 

 lifting and planting, as well as the environmental conditions at the planting site. 

 Changes in seedling physiology during the fall season are not visibly as spectacular 

 as those of the spring. Nevertheless, profound changes do occur within the plant as 

 it responds to shortened photoperiods and cooler temperatures and gradually becomes 

 more and more dormant. A 2-week period during this development could bring about 

 physiological changes that would radically alter the ability of the seedling to cope 

 with transplantation and the conditions of a new environment. Add to this the vari- 

 able and rapidly changing conditions of the planting site environment. The result 

 is an extremely complex set of interactions, which, because of our limited knowledge, 

 defy conclusive explanation. 



In contrast to the situation in the fall, spring lifting and planting conditions 

 are somewhat less variable. With the exception of part of the 1969 spring-planted 

 material, stock was lifted prior to any visible bud activity and placed in cold 

 storage until shipped and planted. The cold environment of the stored seedlings 

 tended to inhibit physiological activities of the seedlings and to keep them in a 

 quiescent condition until exposed to the growth-promoting environment of the planting 

 site. Although physiological changes do occur in trees in cold storage, the changes 

 may not be as great as those that take place in the nursery during equivalent time 

 periods in the fall. Thus we feel that our spring-planted trees were more uniform in 

 their physiological condition than the fall-planted seedlings. 



The contrast between survival of western larch and that of Engelmann spruce when 

 planted at various times within the fall planting season is noteworthy. Larch could 

 not tolerate lifting and planting until mid-October, but spruce survived best when 

 planted in mid-September. Also, larch continues to grow throughout September at the 

 Coeur d'Alene Nursery, but spruce sets winter buds in late August and early September. 

 The increase in size of larch stock as the fall planting season progressed may have 

 contributed to its better performance, but we feel that physiological changes between 

 October 1 and October 15 made the most significant contribution. Threshold photoperiod 

 or temperature occurring during this period probably triggered dormancy and conditioned 

 the stock so that it could be lifted and planted with minimum physiological disturbance. 



As in most coniferous species, the earlier bud set in Engelmann spruce is probably 

 followed by increased root growth, which gradually decreases as the growing season 

 becomes less favorable. Possibly, spruce seedlings that are lifted and planted in mid- 

 September are better able to extend their root systems at the planting site than are 

 those planted later when the fall surge in root-growth activity is declining. A seed- 

 ling that has been able to extend its root system in the fall probably would have a 

 decided survival advantage through the following growing season and subsequent drought. 



The reactions of Douglas-fir and grand fir to planting date within the fall plant- 

 ing period were less pronounced than those of Engelmann spruce and western larch. On 

 the moist sites, both Douglas-fir and grand fir tended to survive best when jilanted 

 early, as did spruce. On the dry sites, the opposite, larch-like trend seeined to 

 prevail, especially with grand fir. This curious interaction of the effects of planting 

 time and aspect upon survival may result from different environmental factors being 

 limiting on the two aspects. On the northerly aspect, declining soil temperatures riav 

 gradually limit fall root growth and reduce the survival potential. In contrast, soil 

 moisture could be the limiting factor on south-facing sites. 



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