158 UNIVERSITY OF COLORADO STUDIES 



Aspen Association. — As noted in the previous paragraph a growth 

 of aspens sometimes forms an intermediate stage in the development 

 of coniferous forest, from sedge or grassland. Only one small grove of 

 aspen is found at Redrock Lake, located near the shore at the northwest. 

 Aspens generally occur in fine-grained soil with some accumulation of 

 humus and do not develop in coarse gravel and disintegrated granite. 

 They are followed, at this altitude, by moist forest of Engelmann spruce 

 and sub-alpine fir. 



Dense Dry Forest. — In those parts of the forest where the soil is dry 

 because of its shallowness or south exposure there may be, nevertheless, 

 a dense tree growth. As a rule Pinus murrayana and Pinus flexilis 

 are the dominant species with only an occasional spruce or fir. On the 

 forest floor, which is well covered by pine needles, the most common 

 plant is Vaccinium oreophilum; while scattered specimens of Polemonium 

 conjertum and certain few inconspicuous herbs make up the sparse 

 flora of shade plants able to exist in these conditions. A few mosses, 

 chiefly Funaria hygrometrica, occur at the bases of trees. Numerous 

 lichens are present on the boulders and, in early autumn, agarics and 

 pore fungi may be found in small number. 



Open Dry Forest. — As in the dense dry forest, Pinus murrayana and 

 Pinus flexilis are the dominant species. Here, however, more xero- 

 phytic conditions prevail. Vaccinium oreophilum, so common a plant 

 on the forest floor elsewhere, is absent. Dry-country plants are the 

 rule. Juniperus sibirica, Lupinus alpestris, Aragallus lamberti, Sedum 

 stenopetalum, Pentstemon alpinum may be named as examples. There 

 are no mesophytes. There is practically neither spring nor autumn 

 flora since in spring there is too much shade for alpine plants and in the 

 autumn the soil is too dry for the growth of even xerophytic foothill 

 species. 



Moist Forest. — This is commonly a close formation of Engelmann 

 spruce with scattered individual pines and firs. A dense cover of spruce 

 needles forms a mulch on the forest floor making it difficult for seedlings 

 to become established. This condition, together with the dense shade, 

 greatly limits the number of species. As in the case of the dense dry 

 forest, Vaccinium oreophilum is the prominent plant of the forest floor. 



