been spotted up to 100 miles away 

 from any metropolitan source. 

 Along with the combustion of auto- 

 mobile and industrial fuels, ozone 

 is added to air by disturbances in 

 the outer stratosphere of the earth 

 and by electrical storms. Ozone 

 probably causes more injury to 

 plants than any other aerial toxicant 

 in the United States. 



The following lists, representing 

 the personal observations and re- 

 ports of many international scien- 

 tists, are a compilation of the known 

 responses by both hardwoods and 

 softwoods to various pollutants. 

 Check these lists before planting. 



A "Tolerant" rating indicates that 

 the tree species displays little or no 

 sensitivity to a specific pollutant, 

 but that it might behave differently 

 under other environmental condi- 

 tions. 



"Sensitive" trees respond to air 

 pollution injury. 



Trees of "Intermediate" sensitivity 

 show some response to air pollu- 

 tants, but they are not truly tolerant. 



(These lists should not be taken 

 as an absolute basis for assessing 

 the responses of trees to pollutants. 

 Considerable local variation must 

 be anticipated, because of genetic 

 and environmental factors.) 



SULFUR DIOXIDE 



SOFTWOODS 



Tolerant 



Intermediate 



Sensitive 



Balsam fir (Abies balsamae) 





• 





White fir (Abies concolor) 





• 





Silver fir (Abies pectinata) 





• 





Lawson cypress (Cupressus lawsonianu) 



• 







Juniper (Juniperus sp.) 



• 







Larch (Larix sp.) 







• 



Engelman spruce (Picea engelmannii) 







• 



White spruce (Picea glauca) 



• 







Jack pine (Pinus banksiana) 







• 



Lodgepole pine (Pinus contorta latifolia) 





• 





Western white pine (Pinus monticola) 







• 



Dwarf mugo pine (Pinus mugo mughus) 



• 







Austrian pine (Pinus nigra) 



• 







Ponderosa pine (Pinus ponderosa) 







• 



Eastern white pine (Pinus strobus) 







• 



Douglas fir (Pseudotsuga menziesii) 





• 





White cedar (Thuja accidentalis) 



• 







Western red cedar (Thu|a plicata) 



• 







Mountain hemlock (Tsuga mertensiana) 







• 



