ROLE OF SEDGES IN COLORADO PLANT COMMUNITIES I27 
be almost any of the species previously noted as belonging to high altitudes. 
Even some of the sedge-moor Carices may here enter the meadow, since the 
limits of plant associations in the alpine zone are not at all clearly marked. 
Xerophytic Car ex Grassland Association Type 
Four xerophytic Carices are especially important as being the dominant 
species of definite associations, often covering areas of considerable extent. 
These associations will be considered in order, beginning at the lower alti- 
tudes. 
{a) Car ex stenophylla Grassland Association. — This is a highly primitive 
association, well developed in open parks of the foothill and montane zones 
Fig. 2. Carex stenophylla Association on an old flood plain at Tolland, Colorado. The 
Carex plants, scarcely a decimeter tall, form a thin sod. At this particular point very few 
plants of secondary species are present, 
in coarse sandy and gravelly soil lacking in humus. Plants of Carex steno- 
phylla are low, generally less than i dm. in height. They spread by means 
of rhizomes and produce a rather thin sod. In dry grassland of a mountain 
park at Tolland, Colorado (altitude 8,889 feet), as previously reported by 
the present writer (5), this associat^'on is well represented. Associated 
plants are such pioneers as Selaginella densa, Erigeron trifidus, Potentilla 
concinna, Potentilla strigosa. As soil conditions become more favorable 
through accumulation of humus the Carex becomes less important, its 
place being taken by such grasses as Festuca, Agropyron, Koeleria, Dan- 
thonia, and Muhlenbergia. The Carex stenophylla association is, then, the 
inceptive stage of typical xerophytic grassland dominated by true grasses. 
