Bergman and Slallard: climax formations 361 



Laihyrus venosus Pteris aqiiiUna 



Lycopodium. clavalitm Pyrola amcricana 



Lycopodiiiin obsciiriim Pyrola scciinda 



Maianthemum canadense Ruhiis triflorus 



Oryzopsis asperifolia Viola conspersa 



Arctostaphylos nva-nrsi and Danthonia spicata are present, usu- 

 ally in abundance, Arctostaphylos forming broad mats over the sur- 

 face of the ground. There were found only in the area of sand and 

 gravel outwash, and were not noted elsewhere. Lycopodium com- 

 planatum occurs in the northeastern part of the state, but has not 

 been observed at other places. 



The following may be present, but usually only as scattered indi- 

 viduals or in restricted areas : Apocynuni androsaemifoliiim, Clin- 

 tonia horeaUs, Comandra unibellata, Habenaria orhiculata, Hepatica 

 triloba and Lathyriis ochroleiicus. 



Piniis resinosa and P. strobus of the climax association begin to 

 invade this associes, especially in any gaps that occur due to wind- 

 falls or to the death of one or a few trees from any cause. Piniis 

 divaricata and Populus tremuloides are both short-lived, the wood 

 of both is brittle, and the trees are easily broken off by wind, so that 

 the opportunity for invasion by the long-lived pines of the climax 

 forest is soon presented. The composition of the climax forest and 

 its characteristic secondary species have already been discussed 

 (page 345) and need not be repeated here. 



b. Secondary Succession in the Larix-Picea Subclimax 



Although the Larix-Picea associes represents only a stage in the 

 development of the climax pine forest, it is a stage which often per- 

 sists indefinitely as a subclimax on account of the great differences 

 in the habitat as compared with that of the climax pine forest. The 

 very different habitat conditions result in marked differences in the 

 vegetation and in a difference in the sequence of successional stages, 

 which makes it necessary to treat secondary successions in tamarack 

 swamps under a special heading. 



The causes work in the same way and may operate singly or to- 

 gether, as indicated elsewhere. Fire as the more destructive agent 

 affects the habitat more profoundly and causes succession to begin 

 at a lower stage. This is especially true if burning occurs during a 



