88 LOGGING 



the means of entrance for the spores of certain fungi ^ which 

 cause a discoloration. The fungi develop most rapidly during 

 warm, sultry weather. Summer-felled timber may be very seri- 

 ously damaged by insects and fungi in from two to four weeks. 



The felling time of trees, such as oak, is sometimes restricted 

 to the late summer and early fall if the timber is to be trans- 

 ported by water because heavy species cut at this season and 

 allowed to dry for from sixty to ninety days will float. 



The logging of hemlock is restricted to the period between 

 May and August, at which time only the bark can readily be 

 removed. As it is a valuable by-product, used for tanning pur- 

 poses, the logger cannot afford to cut the timber without saving 

 the bark. 



Tanbarks are also secured from chestnut oak {Qiiercus priniis) 

 and from the tanbark oak of California {Quercus densiflora) . The 

 season for peeling chestnut oak is from early April until the end 

 of June, and for tanbark oak, from the middle of May to the 

 middle of July. The timber in both cases is now used for com- 

 mercial purposes, although the bark is the more valuable product. 



Coppice fellings should be made during the winter and early 

 spring because the sprouts are then more thrifty than those from 

 trees cut during the growing period.- Late winter felling is 

 preferred because there is less chance for the bark to be loosened 

 from the stool by the collection and freezing of moisture. 



The season of the year in which timber is cut does not, so far 

 as known, influence its strength, although it may affect its dura- 

 bility. Hardwoods are more complex in structure and are more 

 easily damaged in seasoning than are softwoods. Winter-felled 

 hardwood timber air dries more satisfactorily than summer-felled 

 timber because the water content evaporates slowly and the 

 woody structure adapts itself to the gradual shrinkage with a 

 minimum amount of checking. 



^ There are several genera of fungi which attack the sapwood of deciduous and 

 coniferous woods, causing a bluish, blackish or reddish discoloration. The infec- 

 tion takes place largely through spores carried by insects into the galleries that have 

 been made by ambrosia beetles, sawyers and other borers. 



2 See Chestnut in Southern Maryland, by Raphael Zon. Bulletin No. 53, 

 U. S. Bureau of Forestry, 1904, pp. 14-17. 



