48 



BULLETIN 1233, U. S. DEPARTMENT OF AGRICULTURE. 



may fall far short of showing the really critical conditions which must 

 ultimately be examined. In considering these Nebraska tempera- 

 tures, the effects of a scantily covered and strongly mineral soil are 

 apparent in the high daily ranges, which in clear weather often go to 

 40 and occasionally to 50°, while averaging 27.6° for the year and 

 30.4° for the growing season. Thus, for the growing season the mean 

 maxima are 20.7° in excess of those at the control station, while the 

 minima are only 11° in excess, the difference becoming less in late 

 summer. These facts, considered with those of distribution, are at 

 least strongly suggestive that, although yellow pine may make 

 vigorous growth with temperatures which are both theoretic ally and 

 actually very favorable for corn, yet the seedlings at their most 

 sensitive stage must have much more moderate conditions. The 

 relation of these high temperatures to surface drought in such a 

 sandy soil must not be overlooked, especially when it is noted that 

 seeding fails even in well-shaded situations. 



2. The northern Colorado Douglas fir site (F-17) should possess 

 characteristics somewhat similar to those of the control station, as it 

 is similarly situated on the east slope of the mountain range. Its 

 considerably lower winter temperatures, however, indicate that it is 

 not so potently affected by descending winds, and that these may be 

 peculiarly developed in the Pikes Peak region. On the other hand, 

 the southern Colorado station (W-Al) is very much colder than the 

 control station during the winter — the locality being peculiarly free 

 of wind at all times — and appreciably cooler also tnroughout the 

 growing season, although the latter difference is not a serious one. 



If the north slope open and covered stations are used to represent 

 Douglas fir in the Fremont locality, the temperatures for this type, as 

 computed, may be summarized in the following order based on the 

 growing season: 





Growing 

 season. 



Year. 



Locality. 





Highest 



°F. 



57.50 

 i 56. 65 

 i 55. 78 



54.18 

 3. 32 



°F. 

 39. 5S 

 39.59 

 3& 89 

 35. 76 

 3. 83 



Northern Colorado. 

 Fremont, cut-over. 

 Fremont, closed stand. 

 Wagon Wheel Gap, north. 





Lowest 





Total rang* 













U3ased on April, July, and October differences. 



The Douglas fir temperatures, which happen to have been taken 

 entirely at middle elevations, do not show so great a range as those 

 of the yellow pine type. In either annual or growing-season require- 

 ments, the species seems to have a somewhat limit ed range, giving 

 way appreciably to spruce under the lowest temperatures here 

 recorded. Even if the brief record for the south-slope station at 

 WagOD Wheel (lap {\\ 2A) be considered, temperatures in excess of 

 those noted are not, found. The south slope hero shows an excess of 

 about 1 .8° over the corresponding north-slope site, and the conditions 

 thus produced seem to be about the maximum that fir will bear, if t he 

 large summer mortality among seedlings may be taken as evidence. 

 Kurt her evidence of t hie lack of adaptive qualities in fir is found in the 

 f;i<i thai in the Pikes Peak region, as observed by themriter. Douglas 

 fir does not go to such high elevations as the western yellow pine 

 occasional!}' <1 



