Bergman and Siallard: climax formations 375 



When a tamarack swamp is drained and afterward burned, the 

 succession begins usually with the Carex-Calamagrostis associes. 

 As a result of the combined draining and burning, all the character- 

 istic plants of the swamp disappear. The water-content of the habi- 

 tat is still high but much less than if Sphagnum were present. The 

 disappearance of Sphagnum, Larix and other swamp species permits 

 the invasion of species of Carex and Calamagrostis, so that the 

 Larix-Picea stage comes to be replaced by this associes as the first 

 stage of secondary succession initiated by draining and burning. 

 If the area affected be mowed or burned over each year, it may be 

 kept indefinitely in this stage and valuable hay meadows result. If 

 the swamp be kept drained but not mowed nor burned over, a 

 secondary succession culminating in the climax Acer-Tilia forest 

 will ultimatel}^ result. 



In such a case the Carex-Calamagrostis associes is invaded first 

 by Betula pumila and Salix petiolaris soon followed by Salix bebbii, 

 S. discolor and Cornus stolonifera. In the region bordering on the 

 climax pine forest, Alnus incana may also occur. As a result of the 

 invasion of these, the plants of the Carex-Calamagrostis associes 

 are killed out. The swamp gradually fills up by the washing in of 

 soil around the edge, aided by the accumulation of humus from the 

 decay of dead vegetation. The process of filling reduces the water- 

 content of the soil and permits the invasion of Populus and Betula, 

 and occasionally plants of Fraxinus nigra and Abies balsamea. 

 Nearer the pine forest region, Abies is present more abundantly. 

 The invasion proceeds from the edge, gradually encroaching on the 

 swamp. After a time an associes of Populus and Betula, as de- 

 scribed on page 373, becomes established. With the occurrence of a 

 windthrow or by the death of individuals of Populus or Betula, the 

 spaces left vacant are invaded by Acer, Tilia or Ulmns or by two or 

 more of them together. The seedlings of these are able to grow in 

 rather dense shade, and continue to develop until they finally over- 

 top the poplars and birches, resulting in the death of the latter. In 

 this w^ay the climax Acer-Tilia forest, as described on page 367 under 

 normal primary succession, becomes established. The successional 

 stages of secondary succession in drained swamps from the initial 

 stage up to the climax Acer-Tilia forest proceed more rapidly than 

 in normal primary succession, but in stages common to both, the 

 composition of the associes and the secondary species present are 

 essentially alike. 



