288 



LIST OF THK SPECIES OE THE ELYMUS CANADENSIS DUNE ASSOCIATION 



Dominant Species 

 Blymiis canadensis 



Secondary Species 



Sporobolus cryptandnts 

 Bnphorhia polygonifolia 

 Euphorbia coroUata 

 Rhus toxicodendron 

 Artemisia caudaia 



Relic Species 

 Cakile edentida 



Salix lo ngifo lia 

 Cycloloina atriplicifoliuiu 

 Asclepias syriaca 

 Panicuni virgatuin 



THE JUNIPERUS DUNES ASSOCIATION 



When a small dune has been formed by some of the sand-binding" 

 plants, such as Calamovilfa, Primus puiuila, or, less frequently, An- 

 dropogon scoparius, either one or both of two species of Junipcrus 

 may come in and replace them, forming what is called the juniper 

 dune. Bearberry {Arctostaphylos uva-ursi), a heath plant, may be 

 present, but in this region it shows a preference for the sides rather 

 than the crests of dunes. These plants, Arctostaphylos and the two 

 species of Juniper us, seldom intermingle but form adjoining families 

 in the same association. There seems to be no evidence as to which 

 juniper appears on a dune first. Junlperus horizoutaJis, however, is 

 by far the more abundant on the dunes, although Juiiipcrits coniiuunis 

 depressa is just as well developed. It is characteristic of juniper 

 dunes to have the sides as well as the crest densely matted with vege- 

 tation. Junipcrus horizontalis is especially adapted for this (see PI. 

 XLIX, Fig. i). Its prostrate stems form a dense matwork of vege- 

 tation in both winter and summer, which retains considerable sand. 

 The junipers themselves easily keep pace with the infiltration of sand, 

 and by; gTowing outwards permit the dune to grow radially at the 

 same time that it is growing in hight. This figure shows a place 

 where the wind is demolishing the dune. The Calauioi'ilfa which ap- 

 pears midway at the left was carried there when the crest gave way to 

 undermining. These dunes reach an altitude of three to four meters. 

 Higher growth is difficult because most of the sand-blowing winds 

 are parallel to rather than at right angles with the axes of the dunes. 



Junipcrus couiuiunis depressa dunes are less frequent and more 

 gently sloping than those of J^miperus horizontalis. Their sides are 



