ECOLOGY OF ISLE ROYALE. 225 



The forested bog areas are characterized by the dominance of Tam- 

 arack, Black Spruce and White Cedar. As a rule, where the Tamarack 

 is more abundant the White Cedar is less abundant, and the opposite. 

 Where the White Cedar is dominant (as it is in many bog areas, the 

 largest trees being 2 — 314 feet in diameter), the few Tamaracks pres- 

 ent are large and appear as pioneer relicts. The White Cedar, more- 

 over, does not appear with the Black Spruce and the Tamarack in the 

 earliest, wetter stages; but seems to come in only when a drier con- 

 dition has been reached. 



It may also be added that none of these characteristic bog trees are 

 here so closely confined to their bog habitats as to the south of here; 

 but they have a much more general distribution. The Black Spruce, 

 for example, one of the earliest pioneers of the bogs, occurs sparingly 

 distributed in the original forests along with the White Cedar and 

 Balsam Fir; and I have also noted it growing on dry exposed rocks 

 where very little soil was present. The Tamaracks also get out of the 

 bogs and occur sparingly distributed in the upland forests — sometimes 

 in most unexpected places. 



Of all the island conifers the AMes halsamea is easily the most com- 

 mon, and seems to be superseding the spruces and tamaracks. The 

 young seedlings of it grow in dense shade, as well as in more open 

 places. Seedlings of the Balsam Fir come up abundantly under the 

 White Spruces in place of the seedlings of that species which do not 

 seem to be able to endure the shade of the dense forest. It will doubt- 

 less form an important part of the rlimatic forest of the island. 



The Picea canadensis is fairly common along the margins of forests, 

 and in the more open parts — even in the deeper parts of the forest — 

 when it has come in as a pioneer with firs and other conifers of the 

 present generation; but the White Spruces do not seem likely to suc- 

 ceed themselves and become a considerable part of the dominant forest, 

 on account of the inability of their seedlings to withstand deep shade. 



4. Burnings. The burnings and old clearings are everywhere char- 

 acterized by an abundance of Populus tremuloides and Betula papyri- 

 fera, while the undergrowth consists largely of Diervilla diervilla, Aster 

 macrophylla, Chamaenerion angusti folium, Rubus parviflorum, Cornus 

 canadensis, and in places an abundance of Taxus minor. Burnings of 

 different periods were suggested by uniform stands of Quaking Aspens 

 and White Birches which were of different heights. 



The Pennsylvania Cherry {Prunus pennsylvoAiicus) occurs in burned 

 areas and elsewhere where thex'e is little soil, sometimes growing out 

 of the crevices of exposed rocks where the conditions of growth were 

 strikingly unfavorable. Perhaps no other tree on Isle Royale can 

 withstand more xerophytic inland conditions, with the possible excep- 

 tion of the Jack Pine {Pinus divaricata) which was occasionally found 

 associated with it on high exposed ledges. In one locality where the 

 two were growing in close company — a high rocky ledge near Conglom- 

 erate Bay (III, 5) — there was an almost total absence of soil, due 

 to its removal to lower altitudes by wind and rain; there was a strik- 

 ing range of 50°-70° F. in the daily temperature, and a complete ex- 

 posure to the powerful Lake Superior winds which overturn so many 

 trees when they had developed enough heart wood to become rigid and 

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