ECOLOGY OF NORTHERN MICHIGAN. 39 



separated from the mesophytic forests of the slopes by a coniferous society 

 of Tamarack, White Spruce, White and Black Ash, and follows closely the 

 foot of the ridge. The floor of the valley is occupied by a broad beaver 

 meadow^ covered with a luxuriant growth of grasses, sedges and other 

 herbaceous forms, Fig. 20. 



Among the conspicuous forms in this meadow may be mentioned Carex 

 Tnonile, filiformis and viridula, Juncus effusus and tenuis, Agrostis hyemale, 

 Calamagrostis canadensis. Scirpus cyperinus, Deschampsia flexusa, Pani- 

 cularia canadensis, Solidago neglecta and erecta, and the Marsh Bel] flower, 

 Joe Pye Weed, Swamp Milkweed and Nodding Ladies Tresses. The fauna 

 is composed chiefly of the butterflies, Basilarchia arthemis, Vanessa antiopa 

 and Argynnis cybele; the dragon-flies, Sympetrum ohtrusum and Aeschna 

 clepsydra; the grasshopper, Camnula pellucida; and the amphibians, Hyla 

 pickeringii and Rana clamitans. This is also the habitat of the Song and 

 Swamp Sparrows, and there was abundant evidence that it was a favorite 

 feeding ground for deer. 



Station VII. Substation 3. The dams at the west end of the beaver 

 meadow are not now in repair, so that they influence but little the nature 

 of the river, except as small pools, four or five feet deep, are formed behind 

 them, where the current is deflected to one side. In these pools the char- 

 acteristic fish is Couesius plumheus, although the Sucker is sometimes found. 

 The fauna of the river, in harmony with the conditions, is composed mostly 

 of brook and creek forms, such as the Shiner, Nototropis cornutus, and the 

 Dwarf Stickle Back, Eucalia inconstans pygmaea. There is very little 

 aquatic vegetation. 



The mud flats along the river are small and practically devoid of vegeta- 

 tion with the exception of scattered grasses, such as Dulichium arundinaceum 

 and Calamagrostis canadensis, on the dryer portions. The birds that were 

 observed here were the Solitary and Least Sandpipers and the Yellow-legs. 

 On the submerged edges of these flats, the characteristic form is the mollusc 

 Sphaerium simile with which is occasionally associated Anodonta marginata. 



The meadow is the result of an extension of the conditions that normally 

 prevail on the wetter parts of the flood-plain, and with this extension of the 

 habitat there is associated an increase of the grass and sedge zones. When 

 the dams, which are largely formed of Hoary Alder, were constructed, 

 the flood-plain in the broad part of the valley was flooded, and this ponding 

 of the stream, resulted in the killing off of the dryer flood-plain flora. It 

 is not probable that the pond covered the entire valley, but the low adjacent 

 ground between the pond and the sides of the valley would be saturated 

 and subjected to floods, making the conditions favorable for the grasses 

 and sedges and an associated fauna, so that a small meadow analagous to 

 the present one probably existed about its margin. 



No evidence of the extent of the pond now remains, for with the trapping 

 off of the Beaver the dams were no longer repaired and were broken through 

 by the river. The pond was thus drained and the water resumed its former 

 channel. This resulted in better drainage and a consequently dryer sub- 

 stratum in the meadow, so that the meadow forms were able to follow the 

 water as it retreated, while the conditions are, at the present time, becom- 

 ing favorable for the higher flood-plain and deciduous forest forms, that are 

 working in about the margin. That the encroachment of the forest forms 

 will ultimately destroy the meadow by narrowing the habitats of the grass 

 and sedge societies, is evident from an examination of the conditions in 

 localities where the Beaver formerly occurred. For instance, there have 



