70 



BARRINGTON MOORE 



Vol. Ill, No. I 



humus and its influence on rate of growth in certain forests seems amply 

 demonstrated. 



Surface burning in a forest, by adding ashes to the soil, may stimulate 

 growth temporarily; but, since it destroys the nitrogen which is seen. to be 

 such a large factor, and allows the remaining nutrients to be rapidly carried 

 off by rain, its ultimate result must be to seriously check growth. 



n iefti Ti 



Fig. I. On left, pitch pine seedlings, rate of growth in height on unlimed (heavier 

 lines) and on lightly limed soils (lighter lines), showing the strong response to 

 humus. On right, Jack pine seedlings, rate of growth in height on unlimed and on 

 lightly limed soils, showing the influence of humus. 



On the sand to which 4 percent of humus by weight had been added the 

 growth rate was more rapid than on the pure sand, except in the case of cedar, 

 which will be considered below. The difference in the growth of the trees 

 on the pure sand and on the sand plus humus was not great, but distinct. It 

 is interesting that the improvement produced by the addition of the humus 

 to the sand, so far as trees are concerned, bore a closer relation to the pro- 

 portion of humus in the sand by weight than by volume. The amount added 

 by weight was small, 4 percent, and the increased growth of the trees was 

 small. This would indicate that in forests the customary practice of measur- 

 ing the percentage of humus by weight rather than by volume may be the 

 better after all. The growth was, however, only that of a single season, a 

 very short proportion of the life of a tree, and later growth might, show the 

 humus mixed with the sand to have a greater influence than that indicated by 



