402 INTRODUCTION TO PLANT GEOGRAPHY [CHAP. 



give remarkable effects, such as the grassy or flower-decked swards 

 that develop around human habitations, mammahan burrows, or, 

 particularly, the nesting-grounds of Geese, Eiders, and other 

 gregarious wildfowl (Fig. 127). An instance of a different kind 

 is shown in Fig. 128, in which a dense grassy patch is developed 

 around a boulder in an exposed Purple Saxifrage barren overlooking 

 the sea ; to such prominences Birds and predators repair, manuring 

 the ground in the immediate vicinity and doubtless sometimes 



Fig. 127. — Looking down on a luxuriant mossy mat on the manured periphery 

 of a wildfowl nesting-ground in Spitsbergen. The plant flowering on the right, 

 above the matchbox (giving scale), is Yellow Marsh Saxifrage {Saxifraga hircuhis 

 agg.), the flowers on the left are of Alpine Brook Saxifrage {S. rivularis agg.), 

 and the small ones below are of Fringed Sandwort {Arenaria ciliata s.l.). 



bringing in viable seeds. The result is often a luxuriant if limited 

 sward in an otherwise seemingly sterile situation. 



As very little cultivation or other human disturbance has so far 

 taken place in most arctic areas, few tracts bear witness to such 

 change ; on the other hand a common and widespread type of local 

 climax is that engendered by the drifting and late-melting of snow. 

 This tends to take place similarly each year and to lead to char- 

 acteristic vegetational zonation within the area of the drift. The 

 zones produced are of subclimax nature although the outermost may 

 be considered postclimax — especially in the Far North where the 



