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UNIVERSITY OF COLORADO STUDIES 



The greatest single edaphic factor is soil moisture; its effects are so 

 important that they should be accurately noted. Indeed, differences 

 in soil moisture can be recognized without the use of instruments if we 

 compare such associations as sage-brush scrub, Potentilla scrub and 

 willow-birch-honeysuckle scrub. The various grassland associations 

 also show striking differences in soil moisture. Even in a single asso- 

 ciation, as the meadow, it is evident that the different societies which 

 can be there recognized depend for their existence on differences in the 

 water content of the soil. The tall valerian, the small-flowered, low- 

 growing blue Pentstemon, the cream-colored Pentstemon, the large- 

 flowered Erigeron, all so abundant in the meadow formation, do not 

 grow mixed together but have their own places chiefly determined by the 

 moisture of the soil. An interesting study would be to resolve this one 

 association into its separate societies, following carefully the changes 

 which occur in general appearance from week to week through the 

 season and keeping accurate records of moisture in soil samples taken 

 at stations in the different societies. Other problems connected with 

 other associations will occur to the student as subjects for study. 



Tables I and II give records of a few observations on soil tempera- 

 tures and moisture content at East Lake during the summer of 1909. 



TABLE I 



Soil Temperatures at Depth of i Ft. at East Lake, Tolland, Colo., during the 

 Summer of 1909 (Degrees F.) 



Zonation. — An arrangement of plants in zones, 1 or belts, is strikingly 

 illustrated in the vegetation around East Lake near Tolland, and some- 

 what less well shown at Park Lake. Next to the water is a zone of 

 sedges which is followed by willow-birch-honeysuckle and this,- in turn, 



"The name "circum-area" has been suggested by Professor John W. Harshberger for such "zones" 

 as are here described. 



