Bcrcjman and Slallard: climax formations 343 



a more or less indefinite zone of Picea along the border of the 

 swamp. Larix ranges farther to the south than Picea, so that the 

 latter is less abundant as the southern limit of its range is ap- 

 proached. Usually Larix and Picea are intermingled, or sometimes 

 Picea becomes more abundant and replaces Larix more or less com- 

 pletely. 



When Larix is the most abundant species, the growth is less 

 dense, and the smaller reduction of the light intensity may enable 

 the shrubs of the Chamaedaphne-Andromeda associes to persist as 

 long as Larix remains the dominant. Andromeda and Cliamae- 

 daphne disappear first, as they are unable to endure shading, but 

 Ledum may persist as long as the swamp itself remains. 



When the bog becomes filled up with partly decayed Sphagnum 

 and rotted wood, or filled around the edges by the washing in of 

 soil from the sides, Picea and Thuja may replace Larix completely. 

 When they become more numerous than the tamaracks, the shrubs 

 of the Chamaedaphne-Andromeda associes disappear, and the suc- 

 cession advances to the next stage. 



If very extensive areas are occupied by this associes, it may per- 

 sist indefinitely as a subclimax, owing to the slowness with which 

 changes take place that would make possible the invasion and estab- 

 lishment of species of the following Abies-Betula associes. The 

 natural development may be retarded by burning or lumbering, or 

 may be accelerated by draining. 



Secondary species: In addition to Andromeda, Chamaedaphne, 

 and Ledum, which belong typically to the preceding stage but per- 

 sist in the Larix-Picea associes, the following occur as characteristic 

 shrubs of this associes: Ribes hudsonianum, R. triste, Rhamnus 

 alnifolia and Lonicera oblongifolia. Many of the herbs which occur 

 in the Chamaedaphne-Andromeda associes are still to be found in 

 this stage. Others are characteristic of this associes, since in a reg- 

 ular sequence of stages they appear here for the first time and find 

 their best development here. The following herbs occur on hum- 

 mocks of living Sphagnum: 



Drosera rotundifolia Sarracenia purpurea 



Eriophorum gracile Saxifraga pennsylvanica 



Miiella nuda Sin Had na tri folia 



Oxxcoccus oxycoccus Viola blanda 



With the exception of Mitella and Viola, the plants of the above 



