Jennings : A Botanical Survey of Presque Isle, 337 



The Quercus velutina Forest-formation. 



This formation is so closely similar to the forest-formation following 

 the Pinus Strobus forest-formation that its separate treatment is not 

 deemed necessary. The only essential difference noted was the 

 presence of occasional large trees of Pninus and Acer, relicts of the 

 earlier Pninus forest-formation. 



Mixed Formations. 



To the southwest of the Fog Whistle the Panicuni-Arteiiiisia forma- 

 tion gives way, near Long Ridge, to a mixed formation representing 

 the overlapping of the heath and the Myrica thicket-formations (see 

 Plate XXVIII). Here may be seen a struggle between the two forma- 

 tions sometimes resulting in favor of the one, sometimes of the other. 

 Juniperus and Pittus here find apparently equally congenial habitats in 

 either the heath or the thicket so that often a patch of Pinus Strobus 

 forest may be seen originating in a Myrica thicket (see Plate XXIV). 

 There is also a mixing of the principal and secondary species of the 

 two formations, so that in total number of species the mixed formation 

 is richer than either of the pure formations. 



Following this mixed heath-thicket-formation, as the structure 

 may be called, comes a mixed forest-formation derived from the Pijius 

 Strobus and the Prunus forest-formations (see Plate XXXVI). This 

 mixed forest occupies much of the area between Long Ridge and the 

 Yellow and Ridge Ponds (see map of Presque Isle). The disposition 

 of the respective facies is, perhaps, not so much a true mixture as it is 

 a case of promiscuous alternation of various sized clumps of the two 

 formations. The principal and secondary species of each clump are 

 usually those peculiar to the formation represented by the facies of 

 the clump, there being no indiscriminate mingling as in the mixed 

 heath-thicket-formation. 



Following the mixed Pinus-Prunus forest- formation comes finally 

 the same Quercus veluti?ia forest which follows in the normal succes- 

 sions. Such a Quercus velutina forest following a mixed Pinus-Prunus 

 forest is represented in a limited way south of Cranberry Pond. 



The Dune-Thicket-Forest Successions. 



Undoubtedly, in no phase of ecology has there been more field 

 work carried on than in the study of the vegetation of sand-dunes. 



