324 FRANCIS RAMALEY 



arral it is an ecological community intermediate between forest 

 and grassland. It is less stable and permanent than either of 

 these others. It readily gives way to one or the other with 

 slight differences in angle of slope or depth of soil. In this part 

 of Colorado gentle slope and fine-grained soil favor grassland 

 development; steep slope and coarse soil favor coniferous forest. 

 A belt of shrubs will continue to exist along the base of the can- 

 yon wall because more sandy material is continually being 

 brought down from above and because this is again disturbed by 

 rain and wind. 



IV. ANNOTATED LIST OF SPECIES IN SANDY SOIL* 



Juniperaceae, cedar family 



Juniperus sibirica; only where sandy covering is thin and solid rock comes close 



io the surface. 

 Sabina scopulorum; under same conditions as juniper but quite infrequent. 



Poaceae, grass family 



Agropyron richardsonii; in coar. e sand. 



* Agropyron smithii; often in the loosest, most sterile sand, a good sand binder. 



*Bouteloua gracilis; the typical short grass of the present study dominating the 



"Bouteloua consociation." 

 Bromus porteri; in sand with some humus. 

 *Distichlis spicata; dense mats in pure sand. 

 Eriocoma hymenioides; a typical sand species seldom found at such high altitude 



in Colorado. 

 Kocleria gracilis; this widely distributed grass occurs here in coarse sand or in 



disintegrated granite. , 



*Muhlenbergia cuspidata; a short grass which develops on sand having a moderate 



amount of humus. 

 *Muhlenbergia richardsonii; a short grass which forms dense tufts in compact 



sand. 

 Stipa nelsonii; in coarse sand or in sand and gravel. 



Gyperaceae, sedge family 



*Carex stenophylla; in coarse sand and disintegrated granite, often forming thin 

 sod over considerable areas. 



Juncaceae, rush family 

 Juncus ater; only in moist areas of sandy soil. 



1 Stray plants, evidently not regular members of the sand communities, are 

 omitted from the list. The more important species are marked with an asterisk. 



