MacMillan: shores at lake of the woods. 985 



VIII. Coniferous arboreal back strand. The principal plant 

 of this formation is Pinus divaricata, the "Jack pine" of the 

 Minnesota loggers. Yet it is only under certain favorable con- 

 ditions that formations of this plant arise upon the sandy 

 ridges of the Lake of the Woods back strand. It appears from 

 my observations that these conditions are relatively deep ster- 

 ility of the soil, slight exposure to winds, and a low, irregular 

 surface on which, however, pools are not abundantly formed. 

 The clear sand, which is so constantly seen about the roots of 

 the pines, does not appear to become much richer in nitrogen- 

 ous content even when one digs below the surface. A slight 

 contrast therefore arises between this type and the Rosaceous, 

 shrubby back strand, for, in the case of the latter, usually the 

 superficial layers of soil are more sterile than those deeper 

 down. 



IX. Populus arboreal back strand. Favorable areas for the 

 development of this formation appear to be low, fairly nitro- 

 genous soil, with regular surface- contour and infrequent inun- 

 dations. Such back strands are sheltered from strong winds 

 if they are to be perfectly developed, otherwise Populus shrub 

 is formed instead. From the more sheltered localities occupied 

 by such back strand formations, and from the wind-breaking 

 force of the trees it becomes possible for the sand to lie quietly 

 and for dead leaves and other plant products to build up humus. 

 Hence the greater fertility of the soil than where a Populus 

 shrub is established. In the differences which arise between 

 Populus shrub and Populus tree formations I presume the rela 

 tive exposure to wind currents is of no slight importance. It 

 will be observed that, once established, a tree formation acts 

 as a wind-break, and thus accentuates the conditions under 

 which it is supposed to develop most readily in the first place. 



X. Salix arboreal back strand. In this formation, which is 

 developed upon certain special areas, there is an evident adap- 

 tation to the following conditions: a low-lying, moist, some- 

 times inundated, shore, considerable nitrogenous material, 

 absence of surf or heavy winds, and the absence of coniferous 

 formations in the back country reaching the back strand. A 

 Salix back strand formation does not flourish at Lake of the 

 Woods when backed by coniferous vegetation, for in such a case 

 the tree-types of its locality are more probably tamarack or 

 spruce. But when backed by meadows, or by hardwood tim- 

 ber such as Beiula or Populus, the Salix arboreal back strand 

 may maintain itself in great perfection. A fine example of it 



