INTERDUNAL PONDS AND TAMARACK SWAMPS 201 



a willow marginal zone occupied by the typical plants of the 

 usual low, wet area. 



One must expect to encounter many variations from the 

 typical arrangement outlined above. The pond may have 

 disappeared entirely as the floating sedges have overgrown it. 

 The sedge zone may have disappeared and the sphagnum bog 

 may occupy the whole depression, either with or without the 

 tamarack border. The association may be in a still later stage 

 in which the tamaracks only are present, the pond having filled, 

 the floating sedge zone having been displaced by the sphagnum- 

 cassandra association, and this in turn driven out by the advance 

 of the tamaracks. This tamarack association may be gradually 

 disappearing as plant debris accumulates, transforming the bog 

 into a drier area with abundant humus in which the plants of 

 the surrounding highland may establish themselves. 



Most of the animals of the tamarack bog are not peculiar 

 to it but are found in other marshes or swamps. In the water 

 held by the leaves of the pitcher plant there breeds a species of 

 mosquito that is subarctic. Certain orthoptera are the most 

 characteristic animals of the sphagnum bog and its borders the 

 short-winged brown locust, Stenobothrus curtipennis, the striped 

 locust, Mecostethus lineatus, the northern locust, Melanoplus 

 extremis, the marsh ground cricket, Nemobius palustris, and the 

 small brown cricket, Anoxipha exigua. The bog tiger beetle 

 (p. 145) is also distinctive. 



