222 The Breckland 



"grass-headi", Carex arenaria, Calluna vulgaris, Pteridium aquilinum and, 

 locally, Ulex europaeus. Of these species, Carex arenaria and. Ulex europaeus 

 are West European; while Calltma vulgaris, although it stretches far east- 

 wards to the plains of Russia, attains its best development in the west ; and 

 the cosmopolitan Pteridium aquilinum tends, in those parts of Europe with 

 a continental climate, to become a woodland plant. But the behaviour of 

 some of these plants shows an insecurity of teniure suggesting that as 

 dominants they are near their limit. 



With the exception of the community dominated by Ulex europaeus, 

 which is local and has not been studied, there are four major easily 

 recognisable plant communities forming a somewhat bewildering patch- 

 work, whose pattern formed the subject of the first ecological investigation 

 of Breckland. Farrow in a series of illuminating papers' dismissed soil 

 variabihty as the primary cause, and from experimental and detailed 

 observational evidence he explained the pattern in terms of the intensity 

 of rabbit-grazing. All the doininants except Pteridium are grazed. Their 

 palatabihty and power of withstanding grazing vary, and the differential 

 effects of diminishing intensity of grazing can be seen in a series of zones 

 with grass-heath the most heavily grazed, followed by a zone of Carex, 

 and that in turn by Calluna. 



In interpreting the vegetation of Breckland, the importance of the 

 biotic factor must be recognised, but too great emphasis upon it obscures 

 primary relationships between the different dominants. By taking cog- 

 nisance of soil variation and the varying behaviour of the dominants on 

 different soil types, the way is opened to a more exact understanding of 

 plant behaviour and the distribution of the plant communities. The soils 

 of Breckland have this in common that their physical properties vary 

 within a rather narrow range. Open, porous, with a liigh percentage of 

 coarse particles, and with an almost negligible amount of silt and clay, 

 they have a low water-holdmg capacity, although this varies with the 

 amount of chalk stones present. And primarily because of the chalk there 

 is considerable chemical variation. 



The soil over much of Breckland is derived from the chalky boulder 

 clay, which contains roughly 50 per cent of CaCOj and 50 per cent of 

 sand wdth small amounts of silt and clay. By leaching, the CaCOj is 

 removed from the surface downwards. Following its removal the change 

 in acidity brings about the initiation of podsohsation, the leaching of 

 bases, the mobilisation of the sesquioxides of iron and aluminium and their 

 transference to lower layers. These changes result in a complete series of 

 stages in the development of a podsol, from shallow and highly calcareous 

 ' £. P. Farrow, Plant-Life on East Anglian Heaths (1925). 



