224 MICHIGAN SURVEY, 1908. 



pioneer of the two. In parts of the upper, or third, lichen zone there 

 are unusually dense and luxuriant formations of Cladonias, often 50-60 

 feet across. Scattered among the Cladonias were Juniperus nana, J. 

 procumbem, ArctostajiUylos iiva-ursi, and Vacciniuni pennsylvanicuni. 

 The upper, or back ])ortion, of this zone will be designated as the 

 Cladonia-heath zone, for it is here that the real shore heath begins. The 

 back of the heath zone contains numerous young Balsam Firs and White 

 Birches which have worked in irregularly from the adjacent forest. • 



A similar sloping rock shore near our Siskowit cabin camp (V, 4) 

 showed some interesting later stages. The shore was here better pro- 

 tected from waves and wind by the flat neighboring wooded islands ; and 

 the forest development had gone on more rapidly, having extended irreg- 

 ularly from the higher shore down to the very water's edge sug- 

 gesting the ultimate condition elsewhere along the less protected rock 

 shore. There were still open places, suggesting the irregular manner 

 in which the trees had pushed out to take possession of the lower shore; 

 but the forest was here far better established (seemingly on account of 

 the better protection) than elsewhere along the beach where exposed 

 directly to the lake winds and waves. 



As the trees increase in number, and afford better conditions of shade 

 and moisture, vigorous mosses and wood plants begin to invade the 

 Cladonia patches still occupying the more open places. A series of 

 I)hotographs was taken showing various stages of this invasion of 

 under-growth wood plants, from a pure formation of Cladonias to a 

 climax of a dense society of wood plants with not a vestige of Cladonias 

 remaining. These later back shore formations were equally well shown 

 along the heath-forest tension zone at Kock Harbor. 



If carefully worked out the rock shore series, from the water's edge 

 back to the neighboring forest, might be made to rival in interest the 

 lake-bog-forest series, so deserving of more careful study on Isle Royale. 



.'{. Forests. The forests of Isle Royale include about 21 species of 

 trees, 13 of which are deciduous, the remainder evergreen conifers. The 

 paucity of species has been more than offset by a generous distribution 

 and abundance, for the island as a whole is heavily forested. The largest 

 and dominant trees of the present forest are Aiies ialsaniea (Balsam 

 Fir), Betula papyrifcra (^Yhite, or Canoe Birch), and Picca canadensis 

 (White Spruce), with the exception of the western end of Greenstone 

 ridge Vhere Acer saccharum (Hard Maple), Betula lufea (Yellow 

 Birch), and Betula l^rntu (Black, or Cherry Birch) are dominant. 



Between the end of Washington Harbor and Lake Desor there are 

 places where almost pure stands of Hard Maple and birches obtain. 

 The scarcity of Ahicx halsanica here, which is so abundant over almost 

 all other parts of the island, is an interesting matter of speculation. 

 Young Balsam Firs were noted growing in the shade and shelter of 

 the maple groves, and they appeared to be vigorous and thriving, yet 

 scarcely a large fir could be found associated with the maples in this 

 ])art of the Greenstone ridge. An examination of the soil here showed 

 that it is only 4-6 inches deep. This, together with the laterally 

 limited root system exhibited by the larger overturned firs, seemed to 

 suggest that, after attaining a certain height and rigidity, they be- 

 came sufficiently exposed to be overturned by the powerful winds that 

 sweep that exposed part of the Greenstone ridge. 



