CORRELATION OF DISTRIBUTIONAL FEATURES. 511 



respect with the conditions for the Southeastern Evergreen Forest and 

 for the Deciduous Forest, indicating that the western section of the 

 Northern Evergreen Forest is confined in its distribution to a region 

 in which there is a relatively narrow range of physical conditions, in 

 spite of its wide geographical extent. Owing to the mountainous and 

 thinly settled character of most of this region, there is an inadequate 

 series of cUmatological stations from which data may be obtained. 

 This is particularly true of the southernmost portions in New Mexico, 

 Arizona, and California, and of the portions which face the Desert 

 region on all sides of the Great Basin. The climatic conditions of the 

 western Xerophytic Evergreen Forest (see plate 1) are even more 

 poorly known, and this has been a strong consideration in omitting 

 that vegetation from the generalized map. Its conditions would 

 doubtless be found to be generally intermediate between those of the 

 Desert and those of the western section of the Northern Evergreen 

 Forest. 



The length of average frostless season ranges from the minimum for 

 the United States to 307 days, a remarkably great amphtude, which 

 is matched only for the Desert region. The lowest values of this 

 condition are recorded for several stations in the Klamath Lake region, 

 where frost has been observed on every day in the year. The shortest 

 normal frostless season outside these stations is 25 days in length, and 

 this has been taken as the minimum for the United States in view of 

 the fact that there is actually, in any given year, a growing-season for 

 plants even in localities where frost is of average daily occurrence, and 

 that the length of this season is at least 25 days even for Klamath 

 Lake stations. The maximum length of frostless season for this vege- 



TCMKRATUMt 

 DATS IN NORMAl. FlIOSTlCM SXAtON (F. 8J 



Hot Oa»». F. S. 

 Cold Days. F. S. 



PMVSIOLOaiCAt. SUHMATIOH. F. S. 



Normal Oailv Mcan, coldest 14 0**s or VCAK 

 Normal Daily Mcan, Vcaii 



Prccipitation 

 Normal Daily Mcam, F. S. 

 Days in lonscst Normal Rainy Period, F. S. 

 Days in longest Normal Dry Pcrioo, F. 8. 

 Mean Totau Year 



Cvaroration 

 Daily Mean, 1B8T>a, F. S. C 



Moisture Ratios 

 Normal P/E. F. S. Q 



Normal n/Z, F. S. CI 



Normal P/E, Vea* C 



Humidity 

 Normal Mean, F. S. C 



Sunshine 

 Normal Daily Duration, F. S. II 



Moisture-Temrerature Indices 

 Normal P/E i T. F. S., PMYSioLOOiCAL Method C 



Fig. 34. Climatic extremes for western section of Northern Mesophytic Evergreen Forest. 



