U. S. Department of Agriculture, Forest Service 
 
 FOREST PRODUCTS LABORATORY 
 
 In cooperation with the University of Wisconsin 
 MADISON, WISCONSIN 
 
 Mtt . 
 
 COMPARATIVE DECAY RESISTANCE OF HEARTWOOD 
 
 OF DIFFERENT NATIVE SPECIES WHEN USED 
 
 UNDER CONDITIONS THAT FAVOR DECAY 
 
 By GEO. M. HUNT 
 In Charge, Section of Wood Preservation 
 
 Revised 
 June. 1931 
 
Digitized by the Internet Archive 
 
 in 2013 
 
 http://archive.org/details/decayOOfore 
 
COMPARATIVE DECAY RESISTANCE OF HEARTWOOD OF DIFFERENT 
 NATIVE SPECIES WHEN USED UNDER CONDITIONS THAT FAVOR DECAY 
 
 Wood kept constantly dry or continuously submerged 
 in water does not decay, regardless of sapwood or species. A 
 large proportion of the wood in use is kept so dry at all 
 times that it lasts indefinitely. Moisture and temperature 
 are the principal factors that affect the rate of decay; they 
 vary greatly with the local conditions surrounding the wood 
 in service.! When exposed to conditions that favor decay, 
 wood in warm humid areas of the United States decays more 
 rapidly than in cool or dry areas. High altitudes are as a 
 rule less favorable to decay than low because the average 
 temperatures are lower and the growing seasons for fungi are 
 shorter. 
 
 The natural decay resistance of all common native 
 species of wood is in the heartwood. When untreated, the 
 sapwood of practically all species has low decay resistance 
 and generally short life under decay-producing conditions. 
 The decay resistance, or durability, of heartwood in service 
 is greatly influenced by differences in the character of 
 the wood, the attacking fungus and the conditions of expo- 
 sure. Therefore a widely different length of life may be 
 obtained from pieces of wood that are cut from the same 
 species or even the same tree and used under apparently sim- 
 ilar conditions. 
 
 General comparisons of the relative decay resist- 
 ance of different species must be estimates. They can not 
 be exact and they may be very misleading if understood as 
 mathematically accurate and applicable to all cases. They 
 may be very useful, however, if understood as approximate 
 averages only, from which specific cases may vary consid- 
 erably, and as having application only where the wood is 
 used under conditions that favor decay. The following 
 classification of common native species is subject to the 
 limitations mentioned above. 
 
 -A more detailed discussion of the factors that influence 
 the decay of untreated wood in service is given in a 
 mimeograph on that subject which may be obtained from 
 the Forest Products Laboratory, Madison, Wis. 
 
 R800 
 
From service records where available, supplemented 
 by general experience, the heartwood of the following species- 
 may be classed as durable even when used under conditions 
 that favor decay: The catalpas, practically all of the cedars, 
 chestnut, southern cypress, the junipers, black locust, red 
 mulberry, Osage-orange , redwood, black walnut, and Pacific yew. 
 
 Similarly the heartwood of aspen, basswood, cotton- 
 wood, the true firs (not Douglas fir), and the willows when 
 used under conditions that favor decay may be classed as 
 low in decay resistance, while the heartwood of Douglas fir, 
 red gum, western larch, chestnut oak, southern yellow pine, 
 and tamarack may be classed as intermediate. The heartwood 
 of dense Douglas fir, honey locust, white oak, and dense 
 southern pine may also be classed intermediate but nearly 
 as durable as some of the species named in the high dur- 
 ability groups. The heartwood of the ashes, beech, the 
 birches, the hemlocks, sugar maple, the red oaks, and the 
 spruces may be considered on the border line between the 
 intermediate and nondurable groups and can not with assur- 
 ance be placed wholly in either group. 
 
 2 
 
 "The species are listed alphabetically and not in order of 
 their relative durability. 
 
 R800 - - 
 
UNIVERSITY OF FLORIDA 
 
 3 1262 08929 1883 
 
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