ECOLOGY OF NORTHERN MICHIGAN. 33 



The fate of the pines on the exposed top of this ridge, the scrubby nature 

 of the aspens and oaks, and the fact that the tops of a large percentage of 

 the living pines are dead, suggests that the timber lines on some mountains 

 may be greatly influenced by wind. 



Station IV. Substation 3. Beyond the limit of the falling rock fragments 

 on the talus slope, where the rocks have been disintegrated and decomposed 

 to form a soil, the Paper Birch, Mountain Maple, Aspen and Mountain Ash 

 become mixed with the Sugar Maple, Balsam Fir and Bass wood, that 

 .gradually predominate to the exclusion of the Aspen and Mountain Ash. 

 In the forest near the bottom of the slope, Hemlock forms a part of the tree 

 cover and occasionally predominates to such an extent that a hemlock 

 forest results similar in composition to the hemlock forest at the foot of 

 the north slope. More often, however, the Sugar Maple predominates in 

 this forest, associated with the Balsam Fir, Basswood and Ironwood, with 

 scattered Hemlocks, and White Pines, thus making it similar in composition 

 to the mesophytic forest of the north slope with which it is connected through 

 the saddles. The ground cover and fauna are also practically the same 

 and need not be listed. 



Station IV. Substation 2. Owing to the flat nature of its valley, Carp 

 river above Carp Lake is a slow meandering stream that is doing practically 

 no vertical cutting, Fig. 18. It is easily turned from side to side, and, as 

 it is deflected toward one side of its valley, it tends to cut into it, while on 

 the other side of the bend, owing to the decrease in the velocity of the current, 

 part of the load is deposited to form mud flats. The river thus tends to 

 broaden its valley at the expense of the neighboring divides and to build 

 up its flood-plain with a part of the material derived in this way. The 

 material that is not deposited on the mud flats is carried on until the stream 

 reaches Carp Lake, where again owing to its diminished velocity, the stream 

 deposits much of its load in the lake, forming a large delta at the mouth 

 of the river. On the flood-plain of the river, Fig. 18, the deciduous forest 

 either gives way to a. coniferous society characterized by the Tamarack, 

 Spruce, Arbor Vitae and Black and White Ash, which in turn grades toward 

 the river into an extensive alder thicket, or, where the valley is narrow, 

 the coniferous society may be nearly or entirely absent, and the hardwood 

 fores't grade directly into the shrub society. The shrub society is largely 

 composed of the Hoary Alder (Alnus incana} associated with several willows, 

 occasional Tamaracks, and scattered clumps of Red-osier Dogwood. The 

 undergrowth in these thickets is not extensive ; among the more noticeable 

 forms are the Skunk Cabbage, Sensitive and Cinnamon Ferns, Skull Cap, 

 and several species of violets. 



The fauna is characterized by a great increase in the number of birds; 

 the warblers and sparrows are especially conspicuous. This is also the 

 habitat of the Red Backed Salamander (Plethodon cinereus) and the Wood 

 Frog (Rana sylvatica cantabrigensis) . For some undetermined reason, the 

 molluscs seem to be very poorly represented in this society. 



Between the alder thickets and the river, in the broader portions of the 

 valley, there is often a well defined zone, of vegetation characterized princi- 

 pally by the Dwarf Cassandra. Between the two societies the Hoary Alder 

 and Dwarf Cassandra occur mingled with the Wax Myrtle, High Bush Black- 

 berry, American Meadow Sweet, and Few Flowering Cranberry. Toward 

 ^the river, the Hoary Alder, Willows, Red-osier Dogwood and Tamarack 

 occur only in scattered clumps among the Cassandra that forms a low dense 

 thicket. Less prominent but" conspicuous forms in this society are the Pale 



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