224 UNIVERSITY OF COLORADO STUDIES 



of plants is denoted a "formation." In this case "general formation" 

 may be used to indicate the larger aggregations and "formation" be 

 applied to the associations denned in the previous paragraphs. 



In any region it is possible to make the associations many or few, 

 since classification depends largely upon individual judgment. No 

 two botanists are likely to agree in the method of naming or in the 

 number or limits of associations or other communities. 



On account of the altitude of Boulder Park 1 (about 9,000 ft.) with its 

 consequent low summer temperature (the July mean about 56 degrees 

 F.) the plant species are largely different from those of the plains area at 

 Denver or Boulder. Hence the plant communities are also different. 

 The student who wishes to make a comparison with other localities in the 

 state may consult some of the papers noted in the reading list. 



Life Zones. — Within a distance of ten miles of Boulder Park four 

 life zones, as listed below, are represented. The names here employed 

 are such as are readily understood and are the ones used in Europe. 

 Zoologists in America have another set of terms, originally proposed by 

 Dr. C. Hart Merriam, and these are given below in parentheses. 



1. Foothill zone (apparently the upper "Transition" of Merriam). At Rollinsville and 

 farther down the valley this zone is locally represented on south exposures of hillsides 

 even where the general vegetation is that of the montane zone. 



2. Montane zone (apparently the "Canadian"). Boulder Park and the adjacent hills all 

 belong to this zone. It is to be noted, however, that local areas in shaded gulches 

 have a sub-alpine flora. 



3. Sub-alpine zone ("Hudsonian" and part of "Arctic- Alpine"). The district around 

 Jenny Lake and, in general, wherever Engelmann spruce forests form the prevailing 

 vegetation may be classed as sub-alpine. 



4. Alpine zone (part of the "Arctic- Alpine"). Rollins Pass (Corona, Colo.) and all 

 other points above timberline are in this zone. 



Forest, Scrub and Grassland. — For our purposes we may consider 

 any assemblage of trees, or of shrubs taller than a man's head, as forming 

 a forest. The forest may be close or open, may be of wide extent or may 

 consist merely of a fringe of trees along a stream. A scrub consists of 



1 The term park is used in the western United States to designate a broad mountain valley, tree'ess or 

 nearly so, which is surrounded by wooded hil s. Such valleys are often the result of the action of glaciers in 

 modifying the form of an original V-shaped gulch. Sometimes they are due to stream erosion cutting back 

 and forth in an area softer than that up stream or down stream. Often the parks are old lake beds. As a 

 rule there are two or more streams uniting somewhere in a park and all the water flows out of the park through- 

 a single narrow canyon. 



