394 Annals of the Carnegie Museum. 



the water. Several of the secondary species are often able to success- 

 fully complete their growth upon decaying driftwood floating upon the 

 water near the shore. Among these species may be mentioned Radi- 

 cula palustris hispida, Cardamine pennsylvanica, and Erigeron 

 ramosus. 



It is very likely that this formation will eventually fill up the space 

 out to the old piles and will be followed by an Alniis thicket. That 

 the formation has not made more progress in the past has doubtless 

 been due to the proximity of the lake to the east and the consequent 

 drifting of sand, but with the recent closing in of the Horse-shoe 

 Pond on the east, and the further advance of the shore-line beyond, 

 the driftwood habitat will be farther and farther removed from these 

 xerophytic influences, and will approach more and more the conditions 

 of ahydrophytic muck -swamp, passing eventually into the Ulmus-Acer 

 stage. 



Secondary Successions. 



Presque Isle presents but two secondary successions — the Burn 

 Succession and the Cultural or Pasture Succession. 



The Burn Succession. 



Examples of this succession are to be seen in small areas immedi- 

 ately to the south of the east end of Long Ridge and along the ridge 

 to the south of Ridge Pond. The first mentioned area evidently 

 supported in part a mixed formation derived from the Rhus-Alnus 

 thicket and the Prunus-Acer forest formations, and in part sup- 

 ported a patch of the Sorghastruin nutans consocies. During the 

 year following the denudation of the habitat many shoots arose from the 

 uninjured roots of the Rhus typhina and a few shoots of Myrica cafo- 

 liniana appeared. The habitat will likely soon support a well-devel- 

 oped Rlius typhina thicket. 



Where the habitat of the So?ghastruin nutans consocies had been 

 burned over, apparently but little damage had been done. The clumps 

 had not been burned so low as to kill the roots entirely and the grass, 

 although thinned out considerably, appeared again the following 

 season in sufficient abundance to completely dominate the area. 

 Most of the normal secondary species were also present in reduced 

 numbers. 



To the south of Ridge Pond it appears that certain portions of the 

 sandy ridge had been cleared and burned in connection with the build- 



