49 CLAYBERG— UPLAND SOCIETIES 1920] 



followed by maple-beech, although the regenerating climax forest 

 can enter at any stage of the upland secondary series. One of the 

 evidences suggesting equivalency of the thorn, fern, and milkweed 

 societies is that sumac can follow any one, and that any of the three 

 can succeed the fireweed flora. 



Xerarch tree society 



The aspen-white birch-pin cherry society varies much in general 

 form and specific content, so three types (consocies) are found. 

 The dominant trees are Populns tremuloidcs Michx., P. grandi- 

 dentata Michx., Betula alba papyrijera, and Prunus pennsylvanica L. 



Pin cherry-birch. — The birch may be absent. Pure pin cherry 

 stands in particular occur in upland and middle level clearings fol- 

 lowing the thorn society. They can spring up suddenly. In spite 

 of good light the lower branches remain slender and die early. 

 The mode of growth is the arboreal expression of the clearing 

 society type; all are also soft wooded. The pin cherry is eco- 

 logically peculiar in being strongly excurrent, with elongate form 

 and filiform type of branches, wasting the minimum of tissue on 

 laterals and trunk diameter. This gives it great power of vertical 

 elongation, an aid in competition for place in clearings, but makes it 

 short-lived ; so in time it must give way to longer-lived hardwoods. 

 Thus the forest of this type is fairly open, with good herbage. 



Aspen-pin cherry. — This is a dry open xerarch type found 

 along shore, especially on the ridge back of the Nipissing cliff. 

 Often half the trees will be dead and the remainder equally divided 

 between the two species. Herbage is scant or none, and dead 

 twigs and branches are thick below. Such a stand is far opener than 

 either maple-beech or cedar forest, although similar to the cedar 

 in number of dead trees. 



Aspen-Pteris. — This is found more on dry levels inland. The 

 small-toothed aspen dominates (90 per cent or more); the large- 

 toothed aspen is prominent ; and some birch may be found. Being 

 secondary, the herbage below the bracken synfolium suggests a 

 high type of primary forest. The following species are found: 

 Gaiiltheria procumbens L., Cornus canadensis L., Lonicera hirsuta 

 Eat., Corallorhiza spp., and Lycopodium tristachyum Pursh. The 



