Bergman and Slallard: clkmax formations 355 



presence or absence is to be explained by the topography and nature 

 of the lake bottom. 



Young trees of Larix, Bctula pumila, Salix Candida, S. petiolaris 

 and others were found as invaders along the shoreward edge of the 

 Carex-Calamagrostis zone of the secondary succession. Betula 

 pumila and Salix Candida usually occurred farthest out. J\Iore to 

 the shoreward, Larix occurred, and with it or sometimes preceding 

 it were found Ledum and Cornus stolonifera. With the invasion 

 and establishment of Larix and Picea, the original conditions are 

 restored. 



2. BURN OR CLEARING SUCCESSION 

 a. In the Climax Forest 



The removal of the climax forest affects the water-content of 

 the soil to a greater or lesser extent by drying the soil, first by the 

 passage of fire, and second by exposure to the action of sun and 

 wind, in case of either burning or clearing. The light relations are 

 greatly changed also, and many of the characteristic plants of the 

 ground layer in the forest disappear, since they are unable to endure 

 the intense light and increased transpiration attendant thereon. 



Although initiated by distinctly different causes, the course of 

 succession is essentially or, sometimes, precisely the same, the differ- 

 ence being of degree and not of kind. Fires, particularly if of great 

 extent and fierceness, may affect an area more seriously in that all 

 the under-vegetation and even the leaf-mould on the surface of the 

 ground may be burned and removed completely. Seeds and per- 

 ennial underground parts are thus destroyed and succession must 

 begin anew. If such a burn occurs in a region with rock outcrop, 

 the succession may be a primary one beginning with crustose lichens, 

 or a secondary one beginning with foliose and fruticose lichens. 

 Clearing alone would never bring this about. In areas of sand, clay, 

 loam, or mixtures of these, the deeper-lying underground parts and 

 seeds would not be destroyed and would enable the succession to be- 

 gin at a later stage. These two causes often work together, as where 

 the brush and slashings are burned after the valuable timber has 

 been removed. Fires of such kind are less destructive and allow 

 succession to begin at a later stage than would otherwise happen. 



Windfalls, whether affecting a considerable number of trees as 

 a group or only a single individual, give rise to secondary succes- 

 sions. These are to be considered with cleared successions from 



