128 



THE CLIMATIC FACTOR AS ILLUSTRATED IN ARID AMERICA. 



Table 3. 



Unless undue weight is given to the vagaries of a single year, it demands such an amount 

 of calculation that it is not worth attempting. 



Turning now from the method of obtaimng the corrective factors to their application, 

 let us see how they work in actual practise. Let us take as an example the western yellow 

 pine, the tree used by Professor Douglass, and examine first the curves upon which its 

 corrective factors are based, and then the final corrected curves of growth for the last 300 

 j-ears. The yellow pines for which data are available fall into two groups : one from the 

 mountains of New Mexico not far from the ruins which were discussed in previous chapters, 

 and one from Idaho. We will begin with those from New Mexico. The figures for all the 

 trees discussed in this chapter, as has al- 

 ready been said, were placed at the disposal 

 of the Carnegie Institution of Washington 

 by the United States Forest Service through 

 the kindness of the Forester, Mr. H. S. 

 Graves. In the case of the yellow pine of 

 New Mexico the Institution is indebted to 

 Mr. A. B. Recknagel, chief of silviculture in the Forest Service at Albuquerque, New Mexico, 

 who not only gathered most of the data, but had them compiled in his office, and placed his 

 results at our disposal. His data, based on 645 trees from four of the United States forest 

 reserves, are shown in table 3. 



The Gila and Datil national forests are in the southwestern part of New Mexico near 

 the Arizona line, between the ruins of the Santa Cruz A'alley on the west, those of the 

 Animas Valley on the south, and those of the Jarilla Mountains on the east. All three of 

 these groups of ruins are about 150 miles from the center of the Gila forest. The Jemez 

 forest lies in the center of the northern part of New Mexico and adjoins the Pajaritan 

 Plateau, where the ruins of Tuyoni and the Canyon de los Frijoles are situated. The other 

 reserve, the Zuni forest, is in northwestern New Mexico about 80 miles south of the remark- 

 able ruins of the Chaco Canyon and not much over 30 miles from some of the other ruins 

 described in preceding chapters. Thus the forests have approximately the same distri- 

 bution as the ruins with which we have been dealing, but in general lie at greater altitudes 

 than the ruins. "The measurements," to quote Mr. Recknagel, "were all taken within 

 the western yellow pine type between altitudes of 7,000 and 9,000 feet. They were taken 

 in the main body of the western yellow pine type, and therefore can be considered as belong- 

 ing to members of the pure stand of the species." In other words, the trees with which 

 we are concerned grew in the portion of the yellow pine area where the trees grow best and 

 where they are neither at the lower limit, so as to be especially liable to injury by drought, 

 nor at the upper limit, so as to be especially liable to injury by excessively low temperature 

 or long winters. In general, the conditions under which the trees grew were practically ident- 

 ical with those described by Professor Douglass at Flagstaff and the higher regions around 

 Prescott. In the selection of the analyses to be used age was the only criterion. All of the 



50 



75 



100 ia5 150 175 



200 



225 250 275 300 325 Years 



Inches 

 0.60 



0.40 



0.20 



0.00 



Fig. 28.— Curve of Grov\-th and Correction for Age of Yellow Pine in New Mexico, based on 

 j\leasurenieut.s of 272 Trees computed by Mr. A. B. Recknagel. See Table .3a on page 130. 



f No. of trees 

 I used as basis 



