MICHIGAN ACADEMY OF SCIENCE. 211 



each composed of over ten associated species, such as are commonly met 

 with in the vicinity of Dearborn, Wayne, and numerous other places in 

 the county, where it is not at all uncommon to count over twenty species 

 of trees growing on a quarter of an acre. 



The problem is greatly simplified by selecting those species which 

 show the most marked tendency to be limited in local distribution to some 

 given area. With this in view, ten species have been chosen as the ones 

 most decidedly related in their local distribution in the county, to areas 

 where certain optimum conditions exist more or less uniformlv. Thev 

 are believed to be the trees whicli are the most certainly confined to 

 restricted areas, and it has been found tliat these ten trees indicate as 

 many regions wliich, together, cover the county, yet do not overlap. 

 These ten trees are assumed to be the most characteristic elements of all 

 the forests of Wayne County, past, as well as present. 



A portion of this number, like Larix, formed forests of pure growth 

 or like-commensal forests; others, like sassafras, tend to form mixed 

 forests or unlike-commensal forests; others, like hard maple, may form 

 forests of pure growth, but also occur in forests of mixed growth. The 

 list, therefore, falls under three headings, as indicated below: 



I. Species tending to form like-commensal forests. 



These are formed by tamarack (Larix laricina), birch (Betiila alba var. 

 papyrifera), and aspen (Populus tremuloides ), giving us respectively, 

 the tamarack forests, paper-birch forests, and aspen forests. Yet forests 

 of pure growth are rare in Wayne County, occurring as small island-like 

 patches here and there. 



Larix is the most strongly social species of this region and tends, more 

 than any other species, to form stands of pure growth. While the few 

 isolated individuals found here and there in some portions of the county, 

 usually in the vicinity of peaty areas, in Livonia, Greenfield, and other 

 places, would suggest that the species may have been somewhat more 

 common in the past than at present, it is not probable that the numerous 

 lakes and ponds existing in the past, and now all reclaimed by vegeta- 

 tion, ever had the Larix forest stage in the filling-in process, so com- 

 mon in the kettle hole bogs farther inland. Such lakes and ponds, while 

 numerous in the past throughout the northeast-southwest central sand 

 drifted belt of the county, were invariably shallow and have all been 

 reclaimed by vegetation, and, except for Yerkes Lake, near Northville, 

 are now represented by beds of peat. An excellent example is found in 

 northeast Brownstown, showing the final stage in the filling-in process. 

 The peaty areas are covered by wet prairie, formed by social grasses or 

 sedges. There is no evidence to show that such areas were ever occupied 



