FOREST TYPES AND THEIR RELATIONS TO BURNS 

 ON THE GILA NATIONAL FOREST. 



By O. F. Swenson. 



It has been well recognized for a long time that different 

 forest types show distinctive injuries and that they are control- 

 ling influences in the severity and the destructiveness of forest 

 fires. This is especially true in a mountainous region where 

 topography causes a larger number of variable and abruptly 

 marked types than are to be found over level areas. The 

 result is a greater diversity of burn effect in mountainous re- 

 gions which is especially true in the Southwest. 



The effect of different aspects on type offers the greatest 

 contrast as a rule when the north slopes are compared with 

 south slopes. It is common to find north slopes in the Gila 

 National Forest which support perfect stands of high class 

 timber while the south slopes of the same mountains may 

 support a pronounced desert type of stunted, shrubby vegeta- 

 tion which has little density and ground cover. Again, on a 

 northern exposure, one may occasionally find a stand of one 

 species while in the same locality on southern exposure, there 

 may be a pure high class stand of an entirely differenv species. 

 Peculiarly enough, the yield per acre may occasionally be the 

 same on these different slopes, though the trees show a wide 

 variation in diameter, height and form factor. These extremely 

 diversified type conditions, brought about by topographical feat- 

 ures which in turn affect climatic and edaphic conditions, are 

 the controlling factors in the extent and severity of the forest 

 fires. Consequently a study dealing with fire injuries must 

 involve a consideration of the forest types and their relative 

 influence in the causes of fires, injury to timber and to site, 

 and in methods of fire fighting. 



Good opportunity for the study was found in the Mogollon 

 Mountains of the Gila National Forest where the varied topo- 

 graphy gives rise to almost every representative forest type 

 found in the Southwest. The following types are the prevail- 

 ing ones in these mountains : 

 I. Woodland type. 



L Conifers over mesas and dry slopes. 



2. Mixed conifers and broad-leaved trees along stream 



courses. 

 II. Western Yellow Pine type. 





