156 UNIVERSITY OF COLORADO STUDIES 



Arenaria. It is such xerophytic species that form the main part of the 

 vegetation, although some of the species listed for the forest zone are 

 mesophytes. These occur chiefly on north slopes where the soil is 

 moist from melting snow far into June or early July. 



As shown in Table V one-third of the species collected in the forest 

 zone are plants which range to lower altitudes and only 7 per cent, are 

 of alpine distribution. The forest then is invaded to a considerable 

 extent by low-country plants but is not entered to any extent by the 

 plants from higher levels. This is what might be expected from the 

 fact that alpine plants are poor "fighters" and would be unable to 

 compete with the species belonging naturally to the altitude of Redrock 

 Lake. Such alpine plants as do occur are here found in open places 

 where the soil is very dry. Here, in early spring, conditions quite like 

 those of the dry alpine tundra exist and such plants as Eritrichium, 

 Lewisia and Arenaria are able to flourish. 



A better understanding of the forest will be reached if the different 

 conditions there present are fully stated. It is to be remembered that the 

 forest is the natural plant formation of the region around Redrock Lake. 

 The trees grow to moderate size, some of the Engelmann spruces in 

 favorable situations being 6 to 8 dm. (2 to 3 ft.) in diameter. The 

 limber pines are seldom more than 5 dm. (1 . 5 ft.) and often much 

 less. None of the trees are deep-rooted. The soil is very thin and 

 rocks come to the surface in many places. Wind storms from time to 

 time uproot some of the trees, leaving open spaces. When this occurs 

 it may be many years before the gaps are filled with trees. If the bare 

 place is in the drier part of the forest it is likely that it will become occu- 

 pied with xerophytic plants, some of them from the alpine region, but 

 others low-country species. On the other hand, if the open space in the 

 forest is moist — a seepage area — it grows up to Dasiphora and sedges, 

 grasses and gentians. These two types of forest openings are present 

 to the east of Redrock Lake. A short account of these as well as of the 

 differences in the forest itself may be given at this point. 



Arenaria Associations. — This name may be applied to plants of 

 dry openings where soil is stony and there is very little humus. The 

 conifers are at sufficient distance so that there are no pine or spruce 



