DECAY OF STRUCTURAL TIMBER. 



63 



RATE OF DECAY. 



The rate of decay varies according to the species of wood and the 

 part of the tree from which it is taken. Sapwood decays vcrv much 

 more rapidly than heartwood. In many broadleaf species the sap- 

 wood may be attacked by one or more of the wood-destroying fungi 

 within a few weeks after the wood is cut. The most notable exam- 

 ples of the rapid decay of the sapwood are to be found in timbers like 

 beech (Fagus atropunicea (Marsh.) Sudworth), red oak {Quercus 

 rubra L.), and chestnut (Castanea dentata (Marsh.) Borkh.). The 

 relation which the presence of organic matter in the sapwood has to 

 its decay has been a much discussed question. It has generally been 

 thought that sapwood will decay most rapidly when cut from the 

 tree during the period when the organic matter, such as starches and 

 sugars, is present in the largest quantities and is being actively 



so 



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fUTU 



Fig. 10.— Diagram showing relative rate of decay of 2,400 pieces of "hill" and "bottom" red oak. 



Countings made April 26, 1906. 



formed by the tree; that is, during the spring and early summer. 

 This has given rise to the almost universal practice of requiring struc- 

 tural timber to be cut during the winter period, in order to insure 

 a long life. 



From a number of experiments made on a large scale with red oak 

 the writers found that the idea that material cut in the winter un- 

 less susceptible to fungous attack certainly did not hold in all ca 

 Reference to figure 10 shows that red-oak timbers cut in November, 

 1903, decayed more rapidly than did similar timbers cut from the 

 same land and piled in the same locality in June, 1903. A\ hile this 

 single experiment does not necessarily show that summer-cut wood 

 is preferable to winter-cut wood, it indicates very clearly that many 

 of the ideas held for a long time as to the relative value o{ winter and 

 summer cut wood deserve more extensive and careful in 



79152— Bui. 149—09- 



