Figure 1-27. The Washingtonia palm (Washingtonia fili- 

 fera) is ecologically successful in limited areas of south- 

 eastern California, Yuma County, Arizona, and in northern 

 Lower California by growing in rocky stream beds or in the 

 vicinity of springs. Near Palm Springs, California. (U. S. 

 Forest Service.) 



been a long time for adaptation of plants to special habitats. The 

 roots of a number of species, including Arctagrostis latifolia and 

 Eriophorum vaginatum var. spissum, are able to follow, within about 

 1 cm, the melting of the permafrost; thus essential rapid growth 

 at low temperatures takes place during the short growing season. 

 The occurrence of certain rare species, such as Minuartia stncta and 

 its associates in the North Pennines of Great Britain, is possible 

 because of the maintenance of favorable habitats since the Late- 

 glacial Period. ^^3 



High-alpine species often seem to be restricted to the high 

 altitudes partly through lack of competitive capacity. They can 

 hold their own only where the usual growth requirements can be 

 met and where the growing season is so short that all plants with 

 longer growing periods and greater competitive capacity, are 

 eliminated. For example, in Swedish Lapland many alpine 



Ecological CHaracteiristics of Species &. Populations 



57 



