NORTHERN COLORADO PLANT COMMUNITIES 



233 



by an open Potentilla scrub. Still higher on the west and northwest 

 banks, with decreasing soil moisture follows first a belt of meadow and 

 then the dry grassland of the higher ground. At Park Lake in favorable 

 situations it is possible to recognize these same zones and in the same 

 order: sedge, shrub, Potentilla, meadow, dry grassland. Along the 

 south shore of East Lake the following zones occur: sedge, shrub, 

 Potentilla, meadow, forest. 



TABLE 11 



Soil Moisture of Samples Taken at Depth of i Ft. at East Lake, Tolland, Colo., 



during the summer of 1909 (percentages) 



A further distinction of zones may be made in many places if attention 

 be given to particular species of, let us say, the dry grassland or the 

 meadow. Frequently the yellow sulphur flower (Eriogonum umbellatum) 

 and the cream-colored species {Eriogonum subalpinum) grow close 

 together and in parallel zones near the base of a hill. In such cases the 

 yellow species occupies the drier situation. A zone of yarrow {Achillaea 

 lanulosa) is frequently well marked along highways, as the road between 

 Tolland and Jenny Creek. This is best seen about August i. 



In a visit to true alpine lakes or streams above timberline it will be 

 noted that, as a rule, definite belts of vegetation are not developed, 

 although a certain amount of zonation may be recognized. While sub- 

 alpine ponds generally show a Carex and a willow zone, the truly alpine 

 ponds, above timberline, are likely to have only a very imperfectly 

 developed zonation. There may be a mixture of plants of moor, 

 meadow, willow scrub and dry tundra even close to the water's edge 

 and possibly no true belts except along some one small part of the shore. 

 The failure of alpine plants to occur in zones is chiefly due to minor local 

 differences in depth of soil, amount of moisture, presence of large rocks, 

 etc. 



