206 P.J. Webber et al. 



PLANT SUCCESSION AND 

 RESPONSE TO PERTURBATIONS 



The explanation of vegetation patterns can lie in the physiological 

 constraints of the species and growth forms as already discussed and in 

 the change in plant populations as the vegetation recovers from distur- 

 bance or invades new territory. 



Plant colonization of new or disturbed surfaces and subsequent 

 plant succession is an important topic in arctic tundra, especially with the 

 prospect of increasing disturbance associated with the development of 

 natural resources. Unfortunately the problem is complex and really no 

 better understood at the present time than when Churchill and Hanson 

 (1958) wrote their comprehensive review of tundra succession. Too often 

 successional patterns are interpreted by inference without either an ade- 

 quate set of observations through time or dated surfaces (Polunin 1935, 

 Costing 1956, Spetzman 1959, Johnson and Tieszen 1973). Ahhough 

 succession was not a main emphasis of the vegetation studies, a descrip- 

 tion of inferred succession patterns can be useful in interpreting such 

 studies. The plant succession discussion is based largely on field in- 

 ference and the literature. The rates of change in succession are variable 

 and some changes may take a thousand years while others take only a 

 few tens of years. 



Thaw Lake Cycle 



Short-term linear succession is apparent in the Biome research area, 

 but the overriding patterns are cyclic and can be related either to the 

 thaw lake cycle (Britton 1957) or to the colonization of alluvium (Figure 

 6-9). The resulting successional pattern is oversimplified and may only 

 apply to the immediate Biome research area. Only the most commonly 

 followed pathways are discussed; many others are possible. The succes- 

 sional changes are controlled primarily by changes in microrelief and 

 thus drainage regimes. 



Plant colonization on stable floodplain alluvium is rapid. In a few 

 years a good cover develops, made up of species such as Cochlearia offi- 

 cinalis, Stellaria laeta, Phippsia algida, Alopecurus alpinus, Poa arctica, 

 Saxifraga cernua, and Bryum spp. Other plants, including Dupontia 

 fisheri, Petasites frigidus and lichens soon follow, and stands belonging 

 to the Cochlearia meadow type develop. In areas that are not dominated 

 by snow accumulation, stabilization of the sediments allows develop- 

 ment of stands belonging to the Carex-Poa meadow type. Stabilized 

 areas may become drier either by high-centered polygon formation, or by 



