"'' ^- ^tate Col/ege 



CONTENTS. 



PAOE. 



Introduction 5 



Geography and Topography of the Santa Catalina Mountains 6 



Vegetation of the Santa Catalina Mountains 11 



The Desert Region 15 



The Upper Bajadas 15 



The Desert Arroyos and Canons 19 



The Lower Desert Slopes 22 



The Upper Desert Slopes 23 



The Encinal Region 24 



The Lower Encinal 25 



The Upper Encinal 27 



The Forest Region 29 



The Pine Forest 31 



The Fir Forest 33 



Flora of the Santa Catalina Mountains 36 



Phytogeographic Relationships of the Flora 36 



The Desert Flora 36 



The Encinal Flora 38 



The Forest Flora 39 



List of Characteristic Species 41 



CUmate of the Santa Catalina Mountains 46 



Rainfall 48 



Seasonal Distribution of Rainfall 48 



Altitudinal Increase of Rainfall 51 



Soil Moisture 59 



Evaporation 63 



Humidity 67 



Temperature 69 



Length of Frostless Season 70 



Normal Altitudinal Temperature Gradient 75 



The Absolute Minimum of Winter 79 



Departures from the Normal Temperature Gradient due to Cold-air Drainage 82 



Soil Temperature 86 



Correlation of Vegetation and Climate in the Santa Catalina Mountains 88 



The Normal Altitudinal Gradient of Vegetation 88 



The Vertical Distribution of Individual Species 89 



Physical Factors Involved in the Determination of the Normal Altitudinal Gradient 



of Vegetation 91 



Moisture Factors 92 



Temperature Factors 94 



The Role of Topographic Features in Determining Departures from the Normal 



Altitudinal Gradient of Vegetation 97 



The Role of Slope Exposure 97 



The Role of Streams and Flood-plains 104 



The Role of Topographic Relief 107 



General Conclusions 109 



3 



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