TREE SELECTION 15 



years, compared with 200 to 500 for the pines. The sequoias also 

 grow close together, and in the basins are closely surrounded by other 

 vegetation. So fire once in them lingers and injures the tree. Amongst 

 thousands examined the uninjured trunk has been very rare, perhaps 

 less than 1 in 10, as one looks on top of the stump and sees the history 

 of each tree. The large groves of coast redwood show similar history. 

 Though the custom of burning over the area right after cutting may 

 lead to overestimation of the number of ancient fires, the impression 

 is gained from hundreds of stumps that large fire injury is very nearly 

 as common as in the giant sequoia. 



In tree selection the effect of a lightning scar is negligible. The 

 effect of a fire which kills small trees about but does not externally 

 injure the tree under examination is to cause a slight possible diminu- 

 tion in size of rings. In this connection one remembers that fires are 

 more frequent in times of drought and hence exaggerate climatic 

 effects already in the trees. But the effort of a tree to repair a large 

 burnt area changes the ring-size for some distance from the injury and 

 sometimes all about the tree. Hence trees showing large fire injury should 

 not be used. 



COLLECTION PURPOSES 



In securing records of climate in trees, necessarily length and 

 accuracy of record are the two primary considerations. In the previous 

 pages we have dealt with accuracy alone; now we deal with length, 

 always modified by the necessity of preserving accuracy also. 



Cycles and secular changes — The original thought in this study 

 emphasized the tracing of cycles. These are found in relative ring- 

 sizes which can be taken almost at once from the trees without a 

 knowledge of the absolute rain or climatic equivalent. Perfect dating 

 was absolutely necessary and all specimens have received the most 

 careful laboratory handling. It was found by early tests that no especial 

 gain was made by using large numbers of trees (Vol. I, pp. 21-22). 

 But when Huntington studied the big tree for absolute values and 

 secular changes, he did his work on the stump and obtained material 

 which served his purpose without accurate dating. He used many 

 specimens of all ages in order to work out a compensation for age, for 

 that was fundamental. 



Best collection methods — To allow for the needs of each of these 

 purposes the best collection includes, first, long records; second, a few 

 younger trees for the sake of certainty in dating the older trees if 

 recent rings are compressed and doubtful and in order to develop a 

 compensation formula for age of tree; and third, borings in the outer 

 parts of living trees in order to get present-day climatic comparisons 

 and to be perfectly sure of the ring of the current year, which sometimes 

 fails to show on the stump. 



