222 BOTANICAL GAZETTE [MARCH 
1. Humus little harmed.—This is the commonest type of burn 
upon Isle Royale and results in the development of a characteristic 
“burn forest’’ preceding the reestablishment of the climax. The 
composition of such a forest is mainly the outcome of the differing 
success with which the various species withstand the effects of the 
Fic. 51.—Recently burned area on Fic. 52.—Young birch stump sprouts 
Smithwick Island: fireweeds dominant; in a two-year-old burn near Siskowit 
a relict birch at the left; unburned forest Lake 
in the background. 
fire. The coniferous element of the climax forest, consisting of 
Abies balsamea and Picea canadensis, is entirely eliminated by a 
fire of any severity. Betula alba var. papyrifera, on account of its 
dry papery bark, is very inflammable, and the aerial portions are 
quickly destroyed. The underground parts, however, are not 
killed as are those of the conifers. They persist with great tenacity 
through most unfavorable conditions, provided the humus in which 
