322 Annals of the Carnegie Museum. 



tamarack swamp, sandy soils along the Great Lakes, rocky mountains, 

 or gravelly moraines, owes its prominence there to its ability to thrive 

 in light, infertile, and semi-xerophytic soils. Wherever the ecolog- 

 ical conditions are suitable for the growth of more mesophytic trees 

 the white pine is likely to succumb to competition ; .even though its 

 germination may be successful its seedlings cannot endure the dense 

 shade of hemlock or of most hardwood forests. 



The winged seeds of the white pine are often blown for a consider- 

 able distance by strong winds and, as the white pine woods lie 

 immediately to the southwest of the heath at Presque Isle, many white 

 pine seeds find lodgment in the tangled mat of bearberry (see Plates 

 XXIV, XXIX and XXX). There they find in the sandy loam the 

 very best conditions for ecesis, viz., moderate moisture and a low 

 open vegetational covering, which gives protection from the extremes 

 of heat and drought, and yet lets in the rather abundant light, which 

 . is believed to be so essential for the white pine seedlings. Many seeds 

 of the white pine undoubtedly find lodgment in the soil of the sand- 

 plain, but although germination might be successful in certain wet 

 periods, the seedlings could never endure the heat and drought to 

 which they would be exposed. Certain other formations on Presque 

 Isle, however, as the Myrica-thicket and Cranberry-formations, to be 

 discussed later, offer conditions such that a partial occupation by white 

 pine may take place. In no case, however, on Presque Isle does the 

 white pine accomplish ecesis without the presence of more or less 

 humus in the soil, and without the protection afforded by some low 

 shrubby growth of vegetation." 



(The Formation.) 



From what has been said it may naturally be inferred that the 

 heath may eventually be crowded out by the ever-increasing number 

 of white pines, and such is actually the case. A pure white pine 

 forest (the Finus Sfrobus formation) lies immediately to the south of 

 the Light House (see Plate XXXII) and occupies a considerable por- 

 tion of the area contiguous to the western end of Cranberry Pond. 

 Along the shore to the southwest of the Light House this forest ex- 



^« Spring, S. N. "The Natural Replacement of White Pine on the Old Fields 

 of New England." U. S. Dept. Agricul., Div. Forestry, Bull. 63 : 11, 1905. 



"C/". Livingston, B. E. " The Relation of Soils to Natural Vegetation in Ros- 

 common and Crawford Counties, Michigan." Bo/. Gaz., 39 : 31, January, 1905. 



