MICHIGAN ACADEMY OF SCIENCE. 109 



A CATALOGUE OF THE FLORA OF ISLE ROYALE, LAKE 



SUPERIOR. 1 



william s. cooper. 



Introduction. 



This catalogue is a portion of the outcome of two summers' work upon 

 Isle Royale, in the years 1909 and 1910. The main purpose of the study 

 was ecological, and the results have appeared in the four papers noted in 

 the list of literature appended to this preface. The first three are strictly 

 ecological; the fourth may be regarded as supplementary to the present 

 list. 



I have included here a number of species reported by previous collectors 

 upon the island, but not seen by me. These are indicated by an asterisk. 



In describing the habitats of the species listed I have taken pains to avoid 

 such time-honored but meaningless phrases as "hillsides," "glades," "thick- 

 ets," "woods," "rich woods," "open woods," "cool dry woods," "cool moist 

 woods," "rich, dark, moist woods," etc., and have endeavored to define as 

 accurately as possible the habitat of each plant, and to assign it to its suc- 

 cessional place or places. 



For detailed information regarding the plant associations and succes- 

 sions of Isle Royale the reader is referred to a previous paper (No. 6 in the 

 list of literature). It will be well, however, to sketch briefly here the courses 

 of the successions. The climax forest is composed mainly of Abies balsamea, 

 Betula alba papyrifera, and Picea canadensis, and covers the island almost 

 completely. Only along the shores and in bog areas are there tracts of any 

 great extent controlled by other plant associations. It is in the latter situa- 

 tions that we find indications of the successional processes that have re- 

 sulted in the establishment of the climax forest over nearly all of the island; 

 and these situations too are far richer in number of species than is the great 

 mass of the forest. We may distinguish four primary lines of succession, 

 and a fifth which follows the burning of the forest. The rock shore succes- 

 sion progresses through crustose, foliose, and fruticose lichen, crevice, rock 

 pool, heath mat, and xerophytic forest stages to the climax state. The 

 beach succession is unimportant, beaches of any kind being uncommon upon 

 Isle Royale. The bog succession proceeds through aquatic, sedge, shrub- 

 sphagnum, and bog forest stages, ending with the establishment of the 

 climax forest. The delta swamp succession, developing upon the deposits at 

 the mouths of streams, has a similar course, differing in the interpolation 

 of a grass stage after the sedges, and in the absence of sphagnum. The 

 burn succession begins with the "fireweeds," and progresses through a "burn 

 forest," composed mainly of birch sprouts, to the re-establishment of the 

 climax forests, unless the burning has been very severe, in which case the 

 succession is practically a repetition of that characteristic of the rock 

 shores. 



I am greatly indebted to Doctor M. L. Fernald, of the Gray Herbarium 



'From the Michigan Geological and Biological Survey. 



