286 



Relic Species 

 Potcntilla anscrina 

 Juncus balticiis litforali: 

 Xanthiuni coiiuiiidic 



Invading Species 

 Andropogon scopariiis 

 SoUdago graniinifolia 



Calauwvilfa loiigi folia (not com- 

 mon ; it nsually occurs as a lit- 

 tle hill, built up 1-2 dm. above 

 its surroundings) 



Potcntilla fruticosa 

 BquisetiDii hicnialis 



THE PRUNUS PUMILA DUNK ASSOCIATION 



Entering into the composition of the dune-complex to the east- 

 ward of the pines are several steep mounds surrounded and capped 

 by sand cherry {Pniiiiis puiiiila). This plant is a very efficient dune- 

 holder, but no examples of stages in dune formation by it were found. 

 The occasional presence of a Calauiovilfa at the summit indicates 

 that, in this region at least, Primus pninila dunes are formed by the 

 replacement of a dune-originator. The fruit of the Prunus is eaten 

 by a few species of birds among which are two, the song sparrow and 

 the tree sparrow, which occasionally frequent the clumps of Calaino- 

 vilfa. Once the Prunus is started, sand can be easily held by its dense 

 growth. This is too dense for secondary species, but where there is a 

 break, a young Populus candicans may be present. Occasionally on 

 one of these dunes there is alongside of the Prunus puniila a bush of 

 dogwood {Cornus stolonifera), which has much the same habits as 

 the Prunus. The presence of the Cornus is due directly to birds, as 

 this species is avevectant. The robin seems to be the most probable 

 agent, as it has been observed eating the drupelets, and has been seen 

 on the Prunus bushes while drying after a bath in the lake. The dis- 

 tance traversed by the dogwood amounts to nearly a kilometer. 



On account of the dense growth of the dominant species, a Pru- 

 nus puniila dune remains an isolated unit in the dune-complex. In 

 case of the death of the Prunus the sand which it has held is again 

 mobile, and a few wind storms will effect its removal. 



LIST OF THE SPECIES OE THE PRUNUS PUMIEA DUNE ASSOCIATION 



Dominant Species 

 Primus puniila Cornus stolonifera (infrequent) 



Secondary Species Relic Species 



Populus candicans Calamoz'ilfa longifolia (not 



; _ . common) 



