The Vegetation: Pattern and Succession 207 



Carex-Poa 

 meadow 



Dupontia 

 meadow 



Carex- 



Oncophorus 



meadow 



Thaw I 

 lake"" 



Carex- 



Eriophorum 



meadow 



Arctophila 

 pond margin 



FIGURE 6-9. Principal successional trends oj vegetation types and prin- 

 cipal allogenic geomorphic processes controlling them. (After Webber 

 1978.) 



increased drainage as local water courses deepen through thermokarst or 

 frost heaving activity. Drier areas will support Salix and Luzula heaths. 

 Although good field evidence exists for the transition to Luzula heath, 

 such transitions are rare. 



The colonization of drained lake sediments is also rapid. The basin 

 of Footprint Lake has become covered with vegetation within 25 years 

 (Dennis 1977). The present vegetation of the basin varies according to 

 local drainage and substrate composition. It includes Carex-Oncophor- 

 us, Dupontia and Carex meadows, and Arctophila pond margins. The 

 Dupontia meadow is the most abundant vegetation in the Footprint Lake 

 basin at present. Once a surface has a complete cover of vegetation it 

 seems slow to change to another vegetation type. As ice wedge polygons 

 develop, with their attendant variety of microrelief and moisture re- 

 gimes, the vegetation of the Footprint Lake basin should become similar 

 to the highly polygonized Biome research area, but many decades must 

 elapse before the same variety of vegetation types develops in the lake 

 basin. The frequency with which thaw lakes drain and with which new al- 

 luvium is laid down is increased by man's activities. 



The mechanisms responsible for changing vegetation types are pre- 

 dominantly geomorphic. The Carex-Oncophorus meadow can form 

 when polygon troughs drain in a Dupontia meadow. The development of 



