680 JOURNAL OP FORESTRY 



supply. It is also evident that the midsummer rainfall, since it does 

 not begin until July, when height growth has practically ceased, is of 

 little or no consequence, as far as the current year's height growth is 

 concerned. 



The water storage which makes growth possible is mainly the result 

 of the preceding winter's precipitation ; but it is the supplementary sup- 

 ply in April and May which determines whether the growth is to be 

 above or below normal. Records at the Fort Valley Experiment Sta- 

 tion covering the nine years from 1909 to 1917, inclusive, show a mean 

 precipitation of about 8 inches for the winter months, from December i 

 to March 31. The greatest amount recorded for this season is 16.3 

 inches, in 1915-16, and the lowest 5.1 inches, in 1913-14. The great 

 bulk of this comes in the form of snow, which often accumulates to a 

 depth of 3 to 4 feet, representing a water equivalent of 6 to 8 inches 

 on the ground at one time. In some years the snow melts more or less 

 through the winter, as a result of temporary thaws or rains, and then 

 the accumulation is considerably below the above figures. Usually the 

 snow is all gone by April i, and the soil at that time is saturated to a 

 depth of several feet. The penetration depends upon the rapidity of 

 thawing and upon the depth of frost in the ground. Usually the snow 

 goes off with a rush, and if the accumulation is large a considerable 

 portion of the water is lost as run-off. It follows, therefore, that the 

 heaviest snowfalls do not necessarily result in the greatest storage of 

 soil moisture. Observations during the past nine years have shown 

 that even in years of lowest winter precipitation moisture penetrates 

 below the deepest tree roots. Unfortunately a continuous series of 

 deep-soil moisture determinations is not available, but observations 

 made in connection with excavations for improvement work have 

 shown a high moisture content down to 6 feet or more. The following 

 table gives the moisture content at i foot intervals down to a depth of 

 7 feet on June 6, 1913. The precipitation of the preceding winter was 

 6.67 inches, or about i inch below normal, while for April and May it 

 was only 0.09 of an inch. Applying the given wilting coefficient, the 

 moisture available to trees at i and 2 feet is 6.5 per cent, which figure 

 probably holds approximately for the lower strata. 



The stored supply of moisture indicated by the tables would probably 

 be ample if it were all within reach of the tree roots, but this is not the 

 case. Mature trees in this region rarely send their roots down more 

 than 4 feet, while often the depth is less. The average 3-year-old seed- 

 ling has a root only 10.5 inches long. Examinations of 6 of the sap- 

 lings in this study showed that their tap roots extended to depths 



