42 Fire as a Biological Factor. 



and others of this association of the same physiological class, 

 must be more xerophytic in habit than the mesquite. It seems 

 that the flood-plain may be thought of as the home of two quite 

 different sets of plants, one with a tap-root and its branches 

 reaching the water-table, and the other depending upon the 

 water contained in the upper layers of soil; the former approach- 

 ing mesophytic, the latter more definitely xerophytic habits. 



(Continued to March number.) 



FIRE AS A BIOLOGICAL FACTOR. 

 By J. C. Blumer. 



It is a trite but truthful saying that fire is both a useful 

 servant and a dreadful master to man in all walks of life. The 

 prairie farmer made extensive use of it in the early days, at the 

 risk and cost of property and even human life. As a forest 

 fire it has been a much more dreaded destroyer. It is today the 

 most destructive enemy of the forest itself , yet bids fair to become, 

 in certain parts of the West, at least, the forester's most effective 

 aid. As some years ago suggested by the writer for certain high 

 parts of Colorado forests, Mr. E. H. Frothingham now advocates 

 the burning of the humus as a means of reforestation for the 

 dense Pacific Coast forests of Douglas fir. The argument often 

 advanced in favor of fire protection that fire destroys the humus 

 cover, is thus to som.e extent invalidated. Humus, even without 

 forest cover, m.av still do important service as a watershed cover 

 in the conservation of moisture; but it is becoming clear that, 

 especially in the coast forests and forests of high humus-content 

 generallv, destruction of the humus by fire is necessary if the 

 establishment of a young forest is to be successful in the broadest 

 sense of that term. 



Fire is also important from the phytogeographer's view- 

 point. It may have been a factor of far-reaching importance 

 in the establishment of the prairie sod of the Mississippi Valley, 

 the distribution of species, and composition of the societies of its 

 grassy flora. Over the entire Rocky Mountain region it would 

 probably be difficult to find a single square mile of forest that 

 does not show signs of invasion by fire at some time in its history. 

 Many areas can be found that have been razed repeatedly within 

 the history of the passing forest generation. This is conclusively 



