FOREST TYPES IX CENTRAL ROCKY MOUNTAINS. 7 



inapplicable to mountain soils, that considerable ingenuity has been 



required to develop suitable procedure for this study. The aim has 

 been to obtain an accurate measure of soil temperature on the one 

 hand and on the other to determine the moisture content of the 

 soil throughout the growing season. At the same time measure- 

 ments have been made of those more or less stable soil qualities 

 which have an influence upon the availability of soil moisture. 

 After considerable observation and experiment the conclusion has 

 been reached that soil-moisture data can be directly valuable in 

 such a study as this only if they are reducible to terms of exterior osmotic 

 pressure, which is opposed to the osmotic pressure in the plant itself. 

 Although soil-moisture quantities have not been measured in exactly 

 these terms, in the data certain guides are found by which the rela- 

 tive osmotic pressures may be approximated. There remains, how- 

 ever, a great need for further refinement of the data and for new 

 methods especially applicable to the surface of the soil. 



The special conditions affecting the value of the soil moisture and 

 temperature data will be described under these respective captions 

 just before the presentation of the results. 



DESCRIPTION OF THE LOCALITIES STUDIED. 



For the purpose of compilation the stations have been arranged 

 in alphabetical and numerical series, rather than according to the 

 forest types which they represent. The letter represents the initial 

 of the geographic name by which the station is likely to be known, 

 and the number indicates simply the serial order under each letter in 

 this particular study. As the reader is not likely to hold these 

 descriptions in mind and may wish to refer to them frequently, the 

 indexing idea will prevail in then arrangement, except that the 

 control station at Fremont will be first described. 



F-l: Control station. — Elevation, S,836 feet; aspect, S. 15° W.; 

 slope, 21 per cent. Whether this station represents any forest type 

 or will for ages remain a grassy park is very uncertain. It is situated 

 practically on the crest of a narrow east-west ridge, lying only a few 

 feet above stream channels on either side. The ridge represents 

 granite in situ, however, rather than stream deposit. At the exact 

 spot where the instruments are located there were no tree specimens, 

 but a very compact sod. Within 30 feet, on the southerly slope, 

 aspen, limber pine, and 3'ellow pine seedlings were found, the aspen 

 particularly being of very poor development, the nearest trees not 

 over 10 feet high. On the northerly slopes of the same ridge yellow 

 pme, limber pine, and Engelmann spruce form a poorly defined 

 stand. Irregularities in conformation also give room for birch and 

 aspen on this slope. 



In the light of both topographic and vegetal ional evidence, the 

 exact spot at which the station is located must be considered to repre- 

 sent conditions most conducive to a growth of yellow pine or perhaps 

 limber pine. This classification, however, is not so important, since 

 the station was designed primarily to secure data for the general 

 atmospheric conditions of the Douglas fir zone in which it lies; and 

 for the study of either atmospheric conditions or soil conditions one 

 common point of comparison is perhaps as good as another. The 

 records of this station are used in all comparisons of type conditions. 



