DRY GRASSLAND OF A MOUNTAIN PARK 257 



to an earlier type than that through which the road runs, thus 

 in the Muhlenbergia-Aragallus, or in the Muhlenbergia-Dan- 

 thonia society an abandoned road most often shows at first 

 the characters of the Carex stenophylla or even of the Erigeron 

 multifidus society. 



So far as can be judged the Muhlenhergia-Danthonia society 

 represents the ultimate grassland vegetation of the park. It 

 is found now on older stream terraces and on protected parts 

 of the moraine, in shallow glacial sinks and depressions where 

 washing of adjacent slopes results in an accumulation of humus. 

 It is probable that meadow land also on becoming drained gives 

 rise eventually to a society of this general type, although likely 

 with a greater number of flowering herbs. 



Other communities, not a part of the main series noted above, 

 are as follows : 



Agropyron association. This community is named as an 

 association rather than a society because of its striking differ- 

 ence in appearance from the societies that have been named, 

 also because of the existence over large areas along the moun- 

 tain front in the plains region of this ''wheat-grass association."^ 

 Often there is an almost pure growth of Agropyron smithii with 

 only a few straggling intruders from the ordinary dry grassland. 

 The Agropyron association appears on fine-grained and loose 

 soil, especially where it has been turned up by grading for roads 

 or preparing for foundations of buildings. Probably most of 

 the patches of this association here present have developed 

 since the coming of the white man. 



Stipa association. Stipa coviata, S. minor, Eriogonum umhel- 

 latum, Festuca saximontana. This, like the preceding commu- 

 nity, is here named as an association, rather than as one of the 

 societies of the ordinary dry grassland because distinguished by 

 associational rank in the writings of botanists who have studied 

 particularly in the plains region. '^ In some places there are 



* Vestal, Arthur G., 1914, I. c. 

 ' Vestal, Arthur G., 1914, I. c. 



Pound, Roscoe and Clements, Frederic E., Phytogeography of Nebraska, 

 2nd edition. Lincoln, 1900. 



