538 CORRELATION OF DISTRIBUTIONAL FEATURES. 



120, whereas no cold days are experienced within the Hygrophytic 

 Forest. The normal daily mean temperature also ranges to lower 

 values for the tree than for the vegetation in which it is most charac- 

 teristically developed. The temperature conditions encountered by 

 Tsuga in northern Idaho and Montana are otherwise very similar to 

 those in coastal Washington and Oregon. The precipitation condi- 

 tions for the area occupied by Tsuga are very similar to those of the 

 Hygrophytic Forest, at least with respect to the frostless season. 

 Higher intensities of evaporation are encountered in Idaho and Mon- 

 tana and higher values for humidity in northern California, making 

 the amplitudes for both of these conditions somewhat greater than 

 they are for the Hygrophytic Forest. The remarkably wide amphtude 

 of the moisture ratios which is characteristic of the last-named forest 

 is also shown for the area of Tsuga. 



The narrow amplitude in the number of hot days in the frostless 

 season and in the physiological summation of temperature would 

 indicate that these conditions are important in the limitation of Tsuga 

 heterophylla, and the position of the isoclimatic lines also suggest that 

 the precipitation conditions are of critical importance, in spite of the 

 wide amplitude which they exhibit within the distributional area of 

 this tree. 



TCWWKTVIK 



0«T« IM NONM*!. FnotTtCSS SCkSOM (P. S.) I 



Hot Oats, F. S. ■ 



Cold D*y«. F. S. ■ 



Phtsiologic*l SuMM*Tien, F. S. I 



NORM«L DAII.T Mf*N, COLOf (T 14 0*TS OT VuK C 

 NORKOI. 0«ILT MCAH, VC*« 

 PnCCIPITATtON 



Normal Dailt Mcan, F. S. C 



Dat« in lohscst Normal Raint Pcriod. F. S. C 



DATS IN longest NORMAL ORT PcRIOO. F. S. CI 



Mean Total, Vcar ^ 



cvaroration 



Oailt Mean, laST-S, F. S. ■ 



Moisture Ratios 



Normal p/e. F. S. C 



Normal ir/t. F. S. C 



Normal P/E, Year C 



Humidity 



Normal Mean, F. S. C 



Sunshine 



Normal Oail* Duration. F. S. C 



Moisture-Temkrature Indices 

 Normal P/E i T, F. S., Pmtsiolocical Method I 



Fig. 46. Climatic extremes for Tsuga heterophylla. 



Pseudotsuga mucronaia (fig. 47). — The range of this tree covers all 

 of the Northwestern Hygrophytic Evergreen Forest and a large part of 

 the western section of the Northern Mesophytic Evergreen Forest. 

 The climatic extremes for it exhibit some of the features of each of the 

 vegetations with which it is coextensive, and in several cases the 



