FOREST TYPES IN CENTRAL ROCKY MOUNTAINS. 



127 



Surface moisture in the wells was measured for local stations only 

 in 1917, and at Wagon Wheel Gap not at all. 



As the large mass of figures in Table 41 is difficult to grasp, the 

 averages by species groups are presented in Table 42. 



Table 42. — Average "well" moisture for growing season. 



Group. 



Depth. 



Surface. 1 1 foot. 2 feel. 3 feet 



Control station 



Four western yellow pine sites 



Seven Douglas fir sites 



Four spruce sites 



One lodgepole pine site 



Onelimber pine site 



Percent 

 5.72 

 5.13 

 8.59 

 10.18 

 8.84 

 8.56 



Percent, 

 7.59 

 8.75 

 13.33 

 17.90 

 10.53 

 11.80 



Percent. 

 8.19 

 10.14 

 14.78 

 19.92 

 12. 54 

 12.20 



Per cent. 

 9.20 

 11.14 

 15.57 

 21.44 

 15.16 

 13.02 



i Local stations only and season of 1917 only. 



On the face of these data it is very evident that the yellow pine 

 sites possess less moisture during the growing season than do the 

 Douglas fir sites, which, with one exception, are northerly aspects — 

 and likewise that the spruce soils have a still larger supply. It is 

 unsafe to estimate the positions of the limber pine and lodgepole pine 

 sites without some correction for the type of soil involved, as there 

 is here no opportunity for compensating peculiarities. 



In considering the high average values for the spruce sites, however, 

 it is worth while to mention that the group of four was made up of 

 two local stations and also of two at Wagon Wheel Gap whose soils 

 have much better water-holding properties. Thus, for example, 

 the mean 1-foot moisture for the local sites is only 12.5 per cent, 

 or almost the same as for the local Douglas fit sites, but the corre- 

 sponding figure for the heavier Wagon Wheel Gap soils is 23.32 

 per cent. It will be shown later, when wilting coefficients are con- 

 sidered, that this apparent difference is unreal, so far as availability 

 of the water is concerned. 



In the yellow pine group, the relatively high moisture contents at 

 Stations F-4 and F-12 are worthy of note, as both of these sites 

 are fairly favorable for Douglas fir. Of the two, Station F-12 has 

 the more favorable conditions if allowance is made for the quality 

 of the soil. 



As data are available for every site for the season of 1917, which 

 has previously been mentioned as the driest year in which extensive 

 records have been made, it is desirable to give consideration to 

 minimum moisture conditions, which are far more likely to give 

 something significant with respect to the survival of the species. In 

 using the 1917 data, the individual and successive moisture deter- 

 minations are found to be so variable that it seems unsafe to base 

 any conclusions on single observations. The most meager basis 

 would appear to be the average for a month, made up from four or 

 five weekly determinations. The lowest monthly average for each 

 station and depth has, therefore, been accepted. In Table 43 the 

 results are grouped according to the plan of Table 42. 



