24 BULLETIN 544, U. S. DEPARTMENT OF AGRICULTURE. 



decay by that time. There are so many twigs or lops, however, that 

 they must be piled out of the way of logging, and thus elevated from 

 the ground they remain in an an flammable condition for a long time. 

 Windrows of spruce lops even under fairly moist conditions will sup- 

 port the weight of a man, thus showing them to be in comparatively 

 sound condition, at least from 7 to 10 years after cutting. Even 

 if the}' could be scattered over the ground, their bowed form and 

 elasticity would render it difficult to secure an intimate contact with 

 the ground unless they were cut up into small pieces. Their rapid 

 decay is still further hindered by the resinous character of the wood. 



FROST. 



Spruce is rather generally subject to splitting, particularly in very 

 cold exposed situations. This defect is caused by an unequal shrink- 

 age between the heart and sapwood under the action of a sudden drop 

 in temperature below freezing. It may also be accentuated to some 

 extent by the swaying of the tree in the wind when in a frozen con- 

 dition. Spruce having this defect is known among lumbermen as 

 "seamy" spruce. If the grain of the wood is straight, the defect 

 will not cause much loss in sawing; but if it is not straight, the tree is 

 useless except for pulp. As frost crack results from climatic condi- 

 tions, its prevention is not feasible. Spruce is not particularly sus- 

 ceptible to the defect known as "cup or ring shake." 



SUN. 



Trees grown in a dense forest usually have their boles well cleared 

 of branches. Therefore when a portion of the stand is removed 

 injury may result from sun scald through exposure of the remaining 

 trees to direct insolation. The damage is generally confined to the 

 side of the tree facing the southeast, and conditions are most favor- 

 abie to its occurrence hi the late winter and early spring. It may 

 result from the cambium on that side of the tree becoming prema- 

 turely active under the influence of a period of mild weather and a 

 heavy freeze coming on afterwards and killing the new growth. A 

 thawing of one part of the tree under the influence of direct insolation 

 while the rest remains frozen might also cause it. Separation of 

 bark and wood and the collection of moisture in the cavity almost 

 inevitably follow such thawing and afford suitable opportunity for the 

 entrance and development of fungous spores. Such a condition 

 gives rise to a defect known as "spruce canker." 



INUNDATION AND ICE GIRDLING. 



Although spruce will grow and thrive in moist situations, it is 

 permanently injured if not killed outright by inundation, depending 

 upon the duration of the flooding. Spruce is also killed by girdling ' 

 when the inundation is accompanied by the formation of ice about the 

 1 ree trunks. 



'Seen. 57. Bulletin 20. U. S. DeDartment of Aericulturo. Division of Forestry, Oct. 1899. 



