228 Forestry Quarterly. 



Here again we see the trees react to the deficiency in precipi- 

 tation, and the drought year 1908 shows a decrease in the wood 

 increment. Even the ten measurements taken on section 3 N. H. 

 which show the same increment for both 1907 and 1908 when con- 

 sidered separately prove that the tree is affected by the drought. 

 1908, 3556 3.25 2.5 4 3 2.5 3 



1907, 2235 4.00 4.0 4 4 4.0 4 



A clearer and more graphic manner of showing the relation 

 which exists between tree growth and the rainfall is to plot the 

 growth curve as percentages of some one year taken as 100%, 

 usually a year of maximum rainfall and comparing same with the 

 rainfall curve, referred to the same year as 100%. 



The deduction to be made from the above observations and 

 tables is that rainfall is a great factor in tree increment, the 

 location of the tree, however, must be taken into consideration as 

 an exposed and isolated tree is more easily affected than one sur- 

 rounded and protected by other trees, or shielded in some manner 

 from the cold winds. An early warm spring and a continuous rise 

 in the summer temperature with a fair and average amount of 

 precipitation, will cause the tree to flourish and to form a broad 

 annual ring. It is necessary, however, to have at least an average 

 rainfall and this combined with the above meteorological con- 

 ditions will produce healthy and sound wood. Generally the wood 

 increment of the year following the drought year is small and 

 readily observable in the cross section. This is frequently the 

 case although the spring and summer conditions may be the most 

 favorable for tree development. 



