FIRES CAUSED IJY LIGHTXIXG 



437 



grazing has been undertaken this year 

 on six distinct areas. The local stock 

 owners who had previously used the 

 land under lease from the former own- 

 ers have readily accepted the change 

 of ownership and appear to be favor- 

 ably impressed with the methods em- 

 ployed by the Forest Service for graz- 

 ing purposes. While the number of all 

 animals authorized to graze upon these 



southern Appalachian forests is not 

 large, it is the belief of the forest offi- 

 cers in charge of them that under care- 

 ful supervision the lands will support 

 more stock than they have in the past 

 and that there will be considerable im- 

 provement in the individual animals, 

 with a constant increase in meat pro- 

 duction. 



FIRES CAUSED BY LIGHTNING 



EXHAUSTIVE inquiry has es- 

 tablished the fact that lightning 

 ranks next to railroads as a 

 source of forest fires. Forest 

 officers say that the increasing care with 

 fire on the part of the railroads and the 

 public generally tends to make light- 

 ning the largest single contributing 

 cause. 



This statement represents a change 

 of view from that held less than a 

 decade ago in this country, when for- 

 est journals gravely argued whether 

 lightning caused forest fires, though it 

 was known that trees were the objects 

 most often struck. Trees are said to 

 be oftenest struck simply because they 

 are so numerous, and extending up- 

 ward, they shorten the distance between 

 the ground and the clouds ; further, 

 their branches in the air and roots well 

 into the earth invite electrical dis- 

 charges. 



While certain trees are said to invite 

 lightning, and others to be immune 

 from stroke, it seems to be a fact that 

 any kind of tree will be struck, and 

 the most numerous tree species in any 

 locality is the one most likely to suffer. 



Other things being equal, lightning 

 seeks the tallest tree, or an isolated 

 tree, or one on high ground. A deep- 



rooted tree is a better conductor than 

 a shallow-rooted one, and a tree full 

 of sap, or wet with rain, is of course 

 a better conductor than a dry one. 



Lightning sets fires by igniting the 

 tree itself, particularly when it is dead, 

 or partly decayed and punky, or by ig- 

 niting the dry humus or duft' at its 

 base. The forest soil, when dried out, 

 ignites readily, because it is made of 

 partly decayed twigs and leaves, and it 

 can hold a smouldering fire for a con- 

 siderable period. It is probable that 

 most of the lightning-set fires start in 

 the duff. 



In the mountains of southern Cali- 

 fornia, Arizona, and New Mexico there 

 are likely to be each year a number of 

 electrical disturbances known as "dry 

 thunder storms." They come at the 

 end of the long dry season, and being 

 unaccompanied by rain, are very likely 

 to start many serious fires. For this 

 reason the Forest Service has to keep 

 up its maximum fire-fighting strength 

 in those regions until the rains are fully 

 established. In the plans and organiza- 

 tion for fire fighting the service aims 

 l)articularly to catch these unprevent- 

 able lightning-set fires at the time they 

 start. 



Planting 858 .(K)0 Trees 



More than 858,000 young trees are being set out this spring on national forests in Utah 

 and southern Idaho, and the season is reported as particularly favorable to their successful 

 growth. 



