REPRODUCTION OF WESTERN YELLOW PINE. Ill 



Xo studies have been made to ascertain whether the burning of 

 brush piles is attended by any important effects other than the 

 destruction of vegetation. It is reasonable to expect an increase of 

 soil moisture as a result of stopping the root action of grasses and 

 other plants killed by the fire. In the surface layers, however, 

 direct evaporation may decrease the moisture content on bare ground. 

 Burned brush piles and other bare spots during temporary droughts 

 in 1920 showed a perceptible excess of moisture, especially at 

 12 inches, when compared with adjoining areas occupied by a full 

 stand of bunch grass (Table 26). This increase may not always be 

 realized however, because the roots of surrounding vegetation, par- 

 ticularly trees, develop rapidly in the bare spots and soon use up any 

 surplus moisture. Instances have been observed where the spots 

 left by burned brush piles were completely occupied by roots from 

 trees 50 feet distant. Other factors of possible importance are 

 sterilization of the soil and addition of mineral salts found in the 

 ashes. Hesselman (10) has found that in northern Sweden burning 

 stimulates nitrification of " raw humus " and thus greatly favors 

 reproduction of Scotch pine. In view of the practical absence of 

 organic matter in our soils, however, it is improbable that nitrifica- 

 tion is a factor to be reckoned with. Cases have been observed 

 where the surface soil appeared to have been injured by burning. 

 This can be avoided by limiting the size of piles. It is a curious 

 fact that pine seedlings should thrive in these burned spots which 

 other vegetation invades so slowly. This and other questions afford 

 a good field for further investigation. The important fact in the 

 present stage of the investigation is that burned spots and other areas 

 which are bare of herbaceous vegetation are almost invariably re- 

 stocking better than grassy areas. Exceptions to this rule may 

 occur where the destruction of herbaceous vegetation has been ac- 

 companied by packing. The burning of brush piles on such areas 

 can not be expected to improve moisture conditions through the 

 elimination of plant roots. If the soil happens to be a stiff clay, 

 burning may prove positively injurious by consuminig what little 

 surface mold or litter may have been present. All available informa- 

 tion points to the desirability of leaving the brush on bare sites, par- 

 ticularly if the soil is clayey or if the gradient is such as to encourage 

 erosion. 



Reference is frequently made to the benefits supposed to accrue 

 from the decomposition of brush and the incorporation of this 

 organic matter in the soil. Light or moderate applications of 

 brush, as in scattering, produce negligible quantities of humus. As 

 has already been pointed out, however, the semidecayed litter re- 

 sulting from scattered brush aids germination on bare ground. 

 Large accumulations of brush, as in pulled tops or where piles 



