206 NINETEENTH REPORT. 



indicating a possible former vegetated period for the beach if they should 

 prove to be indigenous^ and in either case they give a measure for the 

 reduction of level of the beach by removal of sand by the Avind. 



IV. PROBLEMS. 



It seems desirable to indicate here certain problems which suggest 

 themselves in connection with the study of this region. At present 

 possible lines of solution can only be hinted at but study of their 

 phenomena will be continued, for their solution would tlirow much light 

 on some obscure points in the principles of dune succession. 



A. Character and Cause of tlie Border Zone Formation. It will be 

 noted that this formation is found only on the edge of the climax forest 

 bordering on the bluffs on Lake Michigan and in relic patches on the 

 Point Betsie complex. The species involved are more xerophytic than 

 those of the climax forest. Two factors suggest themselves as chiefly 

 contributing to produce this marked difference in vegetation. One is 

 that of light, for Thuja and Abies balsamea apparently are not shade 

 tolerant, and do not grow to any size when they accidentally germinate 

 in the heart of the climax forest. The other would be the moisture 

 situation, but so far as atmospheric conditions are concerned, atmometer 

 readings show that certain hill tops of the fixed dunes covered by a 

 climax forest have a higher evaporation ratio than this border zone, but 

 they are covered by the characteristic climax formation, except that relic 

 pines and oaks seem more common on these ridges. Soil moisture at the 

 deeper levels may also have something to do with the character of this 

 border zone formation, as soil water must drain away more rapidly 

 tlirough the exposed surface of the bluffs than in portions farther away 

 from the lake. 



B. Distribution of Pinus Strobus. In prehistoric times the sandy 

 plains to the nortlieast of Point Betsie were covered with a heavy growth 

 of Pinus Strobus. This was burned over before the arrival of the white 

 man, who cut manv of the trees which liad been killed bv the fire but 

 which were still standing. From the testimony of the oldest inhabitants 

 there are practically no white pines in the climax forest south of Point 

 Betsie. From other observations it would seem that the beech-maple- 

 hemlock forest extended in a strip 10 or 12 miles wide from Point Betsie 

 south practically to the sandy plains east of Manistee. East of this 

 strip white pine was the characteristic tree. Th^ soil map indicates a 

 region of glacial moraines, just about coterminous with this strip of 

 hardwood forest, while east of this strip is a similarly extensive region 

 of sandy soil. On the other hand, within the Crystal Lake Bar region 

 the climax forest extends apparently without change from the glacial 



