282 JOURNAL OF FORESTRY 



Lightning damage, like windfall, is confined almost entirely to large 

 yellow pine. The mean annual loss in yellow pine on the four ex- 

 tensive plots is 0.16 per cent of the total number. Taking volume as a 

 basis, the percentage would be higher. The loss in black jack is almost 

 negligible, the average number for the four plots being only 0.02 per 

 cent per year. The data for these sample plots were combined by 

 Woolsey* with data from forests throughout Arizona and New 

 Mexico. Among his deductions are the following: 



Tall yellow pines are most liable to be struck ; 23.2 per cent of the 

 trees struck are topped or shattered; about 60 per cent of the trees 

 struck by lightning are killed; beyond the tendency of lightning to 

 strike on high points or ridges, no relation between topography and 

 lightning damage is apparent. 



Insects show sufficient activity to warrant attention. Practically all 

 of the insect damage in trees above the sapling stage is due to bark 

 beetles (several species of Dcndroctonus and Ips). The attacks 

 are at present confined to the killing of occasional trees. There is no 

 record of extensive devastations in this region. Notwithstanding the 

 absence of serious damage, however, the presence of species of bark 

 beetles which are known to have been destructive to western yellow 

 pine in other regions should be regarded as a latent menace capable of 

 assuming dangerous proportions. 



The record of deaths from suppression will prove exceedingly 

 valuable, because -no data on this subject are available. Although the 

 yellow-pine stands in the Southwest are very open, the grouping habit 

 results in the suppression of many trees. The records on "intensive" 

 plots where each tree is numbered and charted will in time prove spe- 

 cially valuable ; but results from such plots are not given here because 

 the period is too short. In fact, the deaths from suppression recorded 

 on "extensive" plots are mainly the result of conditions before cutting. 

 Many trees below merchantable size in dense groups of black jack, 

 however, still remain in a suppressed state. The records will show 

 how long trees of dififerent ages can persist when overtopped and also 

 their capacity to recuperate when released by cutting. 



INCREMENT 



Table 5 shows annual board-foot increments per acre ranging from 

 31.7 to 145.8, and corresponding cubic increments ranging from 5.44 



* Woolsey, Theodore S., Jr. "Lightning Damage in Western Yellow Pine." 

 F. S. Circular Letter SI, D-3, March 10, 1915. (Not published.) 



