Botany in Colorado 27 



Climatic factors might also be called atmospheric factors 

 since they are light, humidity, temperature, wind, pressure and 

 precipitation. Great differences in these factors are imposed 

 upon vegetation at various altitudes and upon various exposures. 



Edaphic factors are in other words soil factors. The water 

 content of the soil is by far the most important of these because 

 of its bearing upon root activities. Other soil factors such as 

 chemical composition may also be of importance, but soil tem- 

 perature, slope, exposure, and surface character are of more 

 importance to the development of the forest. Such soil char- 

 acters as texture and cover are very important when we are con- 

 sidering the reproduction of stands. Vegetation is constantly 

 under the influence of biotic factors, and while the animal life 

 of the forest is usually of little importance, nevertheless it be- 

 comes of extreme importance in the grazing industry in its re- 

 lation to the forest cover. In this form the biotic relations 

 demand the most careful study. The relation of other plants 

 to the forest are also many, but I shall not here enter into a dis- 

 cussion of these principles. 



Climatic and edaphic factors are not always- easy of separa- 

 tion.^ Indeed at present it seems in some cases impossible to 

 distinguish clearly between the effects of climate and soil. In 

 the mountains we find all gradations from precipitous canon 

 sides to jumbled talus slopes. The talus slope when new is free 

 from timber. Later on in life it may become so covered with 

 trees that its early history is sealed for the young investigator. 

 In such places we have great variation in run-off and in the 

 amount of precipitation retained. Many most interesting ob- 

 servations on the results of post glacial weathering may be made 

 in canons where such masses of talus are piled along the bases 

 of the cliffs. At the lower end of such canons may often ^be 

 found a series of terminal moraines with morainal lakes, and for 

 some distance along the sides lateral moraines occur. The 

 floor of such canons especially near the upper course may oftimes 

 be nearly bare, or here and there morainic material may be 

 seen in the form of scattered bowlders. On the smooth some- 

 times polished surface of such places the usual scratches and 

 striae are prominent. Lower down in the valley large areas have 

 a fine-textured soil, while other soil areas are characterized by 

 large particles. This difference is most often a matter of the 

 age of the soil. 



I have already called attention to the telescoped nature of 

 mountain vegetation and to the great differences in the plant 

 cover at various elevations. This arrangement of vegetation 

 superimposed in bands or belts is very commonly called zona- 



