10 DISEASES OF DECIDUOUS FOREST TREES. 



ENVIRONMENTAL DISEASES. 



In a bulletin of this kind it is impossible to more than refer to 

 certain general types of diseases caused by unfavorable environ- 

 mental conditions. Of such conditions the principal ones affecting 

 American broadleaf trees are undoubtedly smoke and injurious gases. 



SMOKE AND SULPHUR GASES. 



In many parts of the United States (7, 37, 71, 109°) extensive 

 areas of deciduous forest lands have been severely injured by the 

 action of smoke or sulphur gases emanating from paper-pulp mills, 

 copper smelters, coke ovens, and blast furnaces. The effects of the 

 sulphur gases first show themselves in deciduous trees either by a 

 discoloration of the young leaves, which ultimately turn mottled 

 yellow and brown and finally die, or by a gradual shriveling and dry- 

 ing of the leaves. A general reduction in the rate of growth likewise 

 takes place, both in the length of the twigs and in the amount of 

 w< »( >d formed by the trunk. 



In both broadleaf trees and conifers the first effect of smoke or 

 gas injury is usually seen in the tops. This refers especially to trees 

 standing together in a forest or in groups. Single trees may first be 

 affected either in that manner or throughout the crown generally. 

 The leaves in the top gradually become smaller and die, while those 

 near the base may be perfectly healthy. The smaller twigs in the 

 top die next, then larger branches, and with long-continued exposure 

 to injurious gases the tree slowly dies downward until it is killed. 



The extent to which trees become diseased as a result of the action 

 of sulphur gases varies materially with the species and the distance 

 from sulphur-gas formation. Buckhout (7) finds twice as much sul- 

 phuric acid in the leaves of white oaks grown three-fourths of a mile 

 from a large range of coke ovens as occurred in similar leaves taken 

 from the vicinity of the Pennsylvania State College. 



The results of an extended investigation on the effect of smelter 

 fumes on vegetation were recently published by Haywood (37), who 

 confirms the extensive experience of European investigators (36, 112) 

 as to the killing effect on vegetation of very small quantities of sul- 

 phur dioxid in the air. Haywood found that in the vicinity of the 

 copper smelters where his investigations were carried on the injury 

 showed itself by the increased sulphur trioxid content of the foliage. 

 He found that the vegetation around the smelter for at least 3 J 

 miles north, 9 miles south, 2 J miles east, and from 5 to 6 miles west 

 had been greatly injured. He suggests that the gases from the 



a The serial numbers used in this paper refer to the bibliography which will be 

 found on pages 69 to 73. 

 L49 



