TECHNICAL NOT E number 990 l OF "_ ._ 6 UNITED STATES DEPARTMENT OF AGRICULTURE FOREST^ SERVICE FOREST PRODUCTS LABORATORY Madison 5. Wisconsin revised"* - p ^ May 1^6 1 COMPARATIVE DECAY RE: OF DIFFERENT NATIVE UNDER CONDITIONS THAT FAVOR DECAY SISTANC^ ^F-^i^'l^UyD E SPECIES WHEN IT.SF.n Wood kept constantly dry or continuously submerged in water does not decay. 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 which affect the rate of decay; they vary greatly with the local conditions surrounding the wood in service. -L When exposed to condi- tions 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 tempera- tures 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 exposure. 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 similar conditions. General comparisons of the relative decay resistance of different species must be estimates. They can not be exact and they may be very mis- leading if understood as mathematically accurate and applicable to all cases. They maybe very useful, however, if understood as approximate averages only, from which specific cases may vary considerably, and as having application only where the wood is used under conditions that favor decay. The following tabulation of common native species in groups according to the decay resistance of the heartwood is subject to the limit- ations mentioned; iReport No. 68, entitled" Factors Which Influence the Decay of Untreated Wood in Service and the Comparative Decay Resistance of Different Species," discusses this matter inmore detail. Copies of the report may be obtained, without charge, from the Forest Products Lab- oratory, Madison 5, Wis. Resistant or very resistant Baldcypress (old growth) Catalpa Cedars Cherry, black Chestnut Cypress, Arizona Junipers Locust, black— Me s quite Mulberry, red- Oak, bur Oak, chestnut Oak, Gambel Oak, Oregon white Oak, post Oak, white Osage -orange- Redwood Sassafras Walnut, black Yew, Pacific Moderately resistant Baldcypress (young growth) Douglas -fir Honeylocust— Larch, western Oak, swamp chestnut Pine, eastern white Pine , longleaf Pine, slash Tamarack Slightly or nonresistant Alder Ashes Aspens Basswood Beech Birches 3 Buckeye- Butternut Cottonwood Elms Hackberry Hemlocks Hickories Magnolia Maples Oak (red and black species)— Pines (most other species)— Poplar Spruces Sweetgum— Sycamore Willows Yellow-poplar ^.These woods have exceptionally high decay resistance. —These species, or certain species within the groups shown, are in- dicated to have higher decay resistance than most of the other woods UNIVERSITY OF FLORIDA in their respective categories Z M 86078 F 3 1262 09216 7617