RELATION BETWEEN HEIGHT GROWTH OF LARCH 

 SEEDLINGS AND W^EATHER CONDITIONS 



By D. R. Brrwster 



Forest Examiner, U. S. forest Service 



It is a common experience in passing" through stands of coniferous 

 seedlings ten to thirty feet tall to notice the rapidly growing leaders 

 of the dominant trees. A casual glance will show a surprising varia- 

 tion in the rate of height growth of the same tree in different years. 

 The obvious explanation that occurs to one is that this variation is due 

 to a corresptjnding variation in the weather in the different years. 



On looking more closely, however, one is disappointed to observe 

 that whereas one tree grew more rapidly this year than last, its neigh- 

 bor just reversed the process and grew more rapidly last year than 

 during the present season. This fact raises the question as to whether 

 or not there really is any relation between rate of height growth and 

 annual variation in weather, and, if so, what that relation is. 



An opportunity for following up this question presented itself dur- 

 ing the past year, in connection with the work of securing growth 

 data on western-larch seedlings. Measurements of 153 trees were 

 taken in two 20-year-old stands at the Priest River Experiment Station 

 in northern Idaho; 41 in one stand November 78, 1916. and it2 in the 

 other, May 11. 191 7. 



Both stands were on level terraces not far from Priest River, the 

 one measured in May being on an upper bench about 50 feet above 

 that measured in November. Soil in both cases was sandy silt, that 

 on the lower bench being somewhat the finer, with a less porous sub- 

 soil. Soil-moisture conditions on the lower bench are better, because 

 of seepage from above and due to a more moisture-retentive soil. 

 Climatically both sites may be considered identical, being not more than 

 one-eighth of a mile apart. .\ meteorological station has been main- 

 tained on the upper bench, about half way between the two stands, since 

 ihe fall of 191 I, ftirnishing a daily record of tenijierature, precijiita- 

 tif)n. wind, sunshine, soil temperatmx, and other physical factors. 



'iVees were selected at random within small restricted areas and the 

 following measurements were taken of each: 



1. Diameter breast high. 



2. .\ge on stmn]). cut as nearly as possible at ground line. 



SOI 



