Bergimui and Slallard: climax formations 363 



quent burning- does not seriously afifect the successional sequence 

 since the water relations of the habitat remain essentially unchanged. 

 The most marked effects are in the changed light relations and in- 

 creased exposure to evaporation. These changes may result in the 

 disappearance of some of the shade-loving plants. 



In extensive swamp areas where filling from the edge can not 

 alter the general conditions of the swamp, the effect of clearing is 

 to permit the development of the bog shrubs which had been sup- 

 pressed by the tamarack and spruce and consequently in the re- 

 establishment of an associes of Ledum, Andromeda and Chamae- 

 daphne. Usually the clearing is not complete, a greater or lesser 

 number of young tamarack and spruce being left. These now de- 

 velop, and with the appearance of new tamarack and spruce, the 

 original Larix-Picea associes soon becomes dominant again. 



In small swamps and in a zone along the edge of larger swamps 

 where the soil is built up more as the result of filling in, an associes 

 of Alniis incana, Cornus stolonifera and species of Salix appear 

 after the removal of Larix and Picea. Betiila pumila, Lonicera 

 oblongifolia, Ribcs hudsonianum and R. triste occur more or less 

 abundantly with these. 



Windthrows are to be regarded as miniature clearings. In a 

 Larix-Picea swamp, when a windfall occurs, its place is invaded at 

 once by Larix and Picea or by either of these alone, which results 

 in keeping the area indefinitely in the same developmental stage in 

 spite of the prevalence of windfalls. This applies in deep swamps 

 where Sphagnum is abundantly developed. 



In swamps that are more nearly filled up and where in conse- 

 quence Sphagnum makes little or no growth, Picea, Thtija, Abies, 

 Betiila and Po pubis appear in the places left vacant by windthrows. 

 Ahius incana, Salix discolor and Corniis stolonifera often come in 

 also, but these are later replaced by the trees named above. As the 

 SAvamp fills up, an Abies-Betula associes becomes established to be 

 succeeded finally by the climax pine forest as the process of filling 

 is carried still further. 



A Larix-Picea swamp, if drained and not disturbed by clearing 

 or burning, gradually fills up, thereby reducing the water-content 

 of the soil. With the draining away of the Avater and filling up, 

 Sphagnum disappears. As the filling up proceeds, Larix dies out, 

 Picea and TJiuja taking its place. In time Abies balsamea, Betula 



