Discussion 



RECOMMENDATIONS 



Results from both tests reported on here show that overwinter 

 storage of planting stock at subfreezing temperatures results in 

 survival and growth rates equal to or better than those obtained 

 with conventional spring lift-cold storage procedures. In only a 

 few situations was the survival of frozen stock significantly less 

 than that of regular stock. Moisture stress plot test results were 

 not completely verified by the field tests, however. In the field 

 test, survival of late planted frozen and fresh stock did not ex- 

 ceed the survival of regular stock as in the moisture stress plot 

 test. The difference in results can probably be attributed to the 

 failure of the stress plot test to provide for decreasing soil mois- 

 ture supply for the later planting. It was thought that keeping the 

 stress plots at relatively high soil moisture levels until July 1 

 would emulate natural precipitation and soil moisture conditions 

 in the field. Either this was not true, or the postplanting soil 

 moisture depletion in the field was more rapid than in the stress 

 plots. Of course, both factors could have contributed to the 

 differences. 



Because of this difference, the stress technique as used here is 

 not recommended for tests that involve variations in planting 

 date. A stress plot test using a modified physical arrangement 

 and improved soil moisture monitoring and control is feasible, 

 however. 



Operationally, the frozen storage technique has great potential 

 value for spreading nursery work, especially stock lifting and 

 packing, over a longer time span. This could result in increased 

 efficiency of operation and better utilization of nursery facilities. 

 Furthermore, seedlings can be lifted in a fully dormant condition 

 and stored at temperatures which effectively retard fungal activ- 

 ity. Complete satisfaction of chilling requirements may be an ad- 

 ditional benefit. 



Seedlings which must be stored until high elevation sites open 

 late in the planting season also store better frozen. Freshly lifted 

 stock, which has neared or reached the end of the initial rapid 

 shoot elongation period in the spring, has good survival potential 

 only if unusually good soil moisture and atmospheric conditions 

 prevail following planting. 



1 . Frozen storage over winter of Engelmann spruce, lodgepole 

 pine, and western larch, in the manner described, simulates na- 

 tural overwinter conditions. It is feasible and offers important 

 advantages over other storage methods, especially for stock to be 

 planted late in the planting season. 



2. Regardless of the storage regime used, early planting results 

 in better survival and subsequent growth. Fall lifting and over- 

 winter storage should facilitate early planting, especially in years 

 when weather conditions preclude early lifting of stock at the 

 nursery. 



3. Frozen storage is probably extendable to other western con- 

 ifers. Validation of this assumption is needed. 



4. Planting freshly lifted stock late in the planting season, 

 after most stem elongation has taken place, is biologically feas- 

 ible, but operationally difficult. Such planting may give survival 

 rates well above those of trees coming out of long-term storage, 

 but fresh stock of this sort must be replanted very soon after lift- 

 ing to avoid severe mortality. Such stock must be treated del- 

 icately in the interval between lifting and planting. It is better to 

 plant dormant trees early in the season for both growth and 

 survival. 



5. More study is needed to determine the effects of fall lifting 

 dates on the survival and growth potential of stock stored over 

 winter and on methods to determine when stock is physiologic- 

 ally ready for lifting. Until information is available, it is recom- 

 mended that stock not be lifted prior to November 1 or until 

 there is suitable evidence that the stock is "dormant" and that 

 food reserves are at a high level. The current practice at the 

 Coeur d'Alene Nursery involves testing the plants' activity status 

 using the oscilloscope technique described by Ferguson and 

 others (1975). Plants are not lifted until 2 weeks after they show 

 a "dormant" oscilloscope trace. 



6. The described frozen storage may provide for more com- 

 plete satisfaction of the "chilling requirements" of Engelmann 

 spruce buds leading to more normal bud break and shoot growth 

 than that obtained with other lifting and storage procedures. 



7. Methods and studies of overwinter cold storage of nursery 

 stock are well documented and the procedure can be made oper- 

 ational in most cases if cold storage facilities are available. 



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