149 



On the other hand, cottonwood (Populus), basswood (Tilia), and 

 silver maple (Acer saccharinum) decay rather rapidly. I have found 

 little definite information on the rate of decay of our trees. The 

 most definite information I have found concerning the durabil- 

 ity of wood in contact with the soil is in a study of fence posts 

 by Crumley ('lo). He shows that heartwood is particularly liable 

 to decay (1. c, pp. 613-614). He gives (pp. 634-635) the following 

 scale of durability, beginning with the most durable; Osage orange, 

 yellow locust, red cedar (woodland grown), mulberry, white cedar, 

 catalpa, chestnut, oak, and black ash. The following have poor dura- 

 bility: honey-locust, sassafras, black walnut (young trees; old trees 

 are durable), butternut, and elm. Red cedar growing "in the open 

 is about the same as oak in durability." These observations aid in 

 giving some idea of the relative rate of decay of logs and stumps in 

 contact with the soil. In the West, Knapp ('12, p. 7) has shown 

 that the upper part of the bole of fire-killed Douglas fir "deteriorates 

 more rapidly than the lower part because of the larger proportion 

 of sapwood. . . . Down timber is less subject to insect attacks than 

 standing timber but decays more rapidly." Hopkins ('09, p. 128) 

 publishes a photograph of an Engelmann spruce forest, at an eleva- 

 tion of 10,000 feet on Pike's Peak, which was killed about 1853-56, 

 about fifty years previously ; there were, however, still preserved on 

 the trunks, the markings of the beetles which killed the trees. The 

 rate of decay in warm moist regions is relatively more rapid than 

 that in cool and dry regions. 



As wood decays it loses the characteristics which distinguish the 

 living and solid trees. For this reason we anticipate that animals 

 showing a preference for different kinds of trees are more charac- 

 teristic of the living and sound wood, and decline in numbers as 

 disintegration progresses, being replaced by the kinds which live in 

 and upon decaying wood. There is thus with the decay of wood a 

 progressive increase in the kinds of animals characteristic of humus. 

 This is true in general terms, for certain animals even show a pref- 

 erence for certain kinds of decayed wood, while others are general 

 feeders upon almost any kind of such wood. Hamilton ('85, p. 48) 

 has observed that "Cucujus clavipes feeds on locust, maple, sycamore, 

 wild cherry, hickory, white oak, elm; Clinidium sculptile on spruce, 

 hemlock, tamarack, black oak, hickory, chestnut, ash, gum, poplar, 

 birch ; Synchroa punctata on all species of oak, hickory, apple, cherry, 

 mulberry, Osage orange, chestnut; Dendroides canadensis on nearly 

 everything." 



The decay of wood begins when moisture and fungi are able 

 to gain entrance, as at some point of injury — an insect burrow, a 



