36 VEGETATION OF BLAKENEY POINT. 



Colonisation and Succession. 



From an examination of the various phases of shingle bank 

 succession there seems little doubt that the primary colonisers 

 are usually forms with extensive root systems, such as Arenaria 

 peploides and Silene maritima, followed on closely by Rumex 

 trigranulatus. The main bank must doubtless be viewed as 

 exhibiting an early condition in pebble beach colonisation, 

 which condition is rendered permanent by its mobility. On the 

 intermediate " Yankee " bank (p. 34) we still find most of the 

 plants of the main bank, but with the addition of species of 

 more stable situations. 



On the older laterals of the Marams the open association has 

 given place to an almost continuous turf, in which the early 

 colonisers are less and less abundant ; thus in the Marams 

 series we find Silene maritima with less and less frequency, 

 Arenaria peploides is only on banks Nos. 6 and 8, and Rum'ex 

 trigranulatus, although present on all but three, is rare in every 

 case, but most frequent on the first and second. Some of the 

 annual species, such as Senecio vulgaris, Sonchus oleraceus, 

 and Myosotis collina, which were frequent on the main bank, 

 have been entirely driven out. 



In marked contrast is the increase of those plants which 

 prefer a stable habitat, such as Sedum, Armeria, Agrostis, 

 Lepturus, and Triticum junceum. Besides which there is a 

 steady influx of gravel heath plants. On the " Yankee " bank 

 these last are represented by a few species only, and these in 

 no great abundance ; they comprise Air a prcecox, Filago 

 minima, Lotus corniculatus, Plant ago Coronopus, and Rumex 

 acetosella, the last being the most common. Such become 

 much more numerous both in species and in individuals on the 

 high elbows of the older laterals. 



Factors Determining Distribution : Case of Statice 



binervosa. 



There seem then to be two factors of prime importance 

 which together determine plant distribution on the shingle ; 

 these are stability and the amount of accumulated soil, the latter 

 in part depending on the former. The importance of stability 



