148 UNIVERSITY OF COLORADO STUDIES 



flora which is nearly absent in the other localities. Especially is the 

 absence of spring flora to be noted in the sedge zone where the soil is 

 cold even through the month of June. The high temperature of the 

 lake is accounted for by the slight depth of water. 



Soil Moisture Observations. — Samples were taken at a depth of 

 about 3 dm. with a soil borer, put at once into tight cans and weighed 

 the same afternoon or the following day. After this they were dried in 

 an oven to constant weight. In the printed figures all fractions have 

 been omitted for sake of clearness. An examination of the averages in 

 Table IV shows that the plant formations may be arranged as follows 

 in order of moisture content : (1) sedge zone; (2) shrub zone; (3) Engel- 

 mann spruce forest; (4) Dasiphora association; (5) Arenaria association. 

 The last, together with the dry pine forest, is xerophytic; the first four 

 formations here named are mesophytic. 



No study of non- available moisture was made but this may be 

 roughly estimated by comparison of work by other investigators. In a 

 field study by Hedgcock 1 at Lincoln, Neb., in the summer of 1900 it was 

 found that the non-available water in "hard loam" was from about 

 5 to 6 per cent, for xerophytic plants. Since the soil of the Arenaria 

 associations is a hard loam and coarse sand or gravel mixture the per- 

 centage would be less ; but it is evident that there is very little available 

 water any time during the summer. It is also to be remembered that 

 the very low soil temperature in all the formations restricts the activity 

 of roots, making them less able to absorb water from the soil. A series 

 of studies on soil moisture of mountain districts is planned for the 

 summer of 1909. 



IV. Z0NATI0N 2 



General Account. — Redrock Lake was chosen for study because of 

 the sharply marked zonation presented. A belt of sedges extends all 

 the way around the lake followed by a belt of dwarf willows and birches, 

 which, in turn, is surrounded by coniferous forest (see Figs. 1 and 7). 



1 Hedgcock, George G., "The Relation of the Water Content of the Soil to Certain Plants, Principally 

 Mesophytes," Studies in the Vegetation of the State, II (Botanical Survey of Nebraska, VI), p. 74, 1902. 



' A preliminary account of the zonation of mountain lakes was presented by the writers at the Chicago 

 meeting of the American Association for the Advancement of Science and the abstract was printed in Science, 

 n. s., Vol. XXVII, p. 208, 1908. 



