Botany 49 



has probably gone 011 for centuries. It is evident that although bush 

 colonisation will be prevented by tliis practice, yet the peat level will 

 continue to rise, and new successions, still subject to the cutting factor, will 

 take place. These will, however, differ from the primary succession and 

 give rise to conmiunities not found therein. Such are the "mixed sedge" 

 and "litter" which cover almost 50 per cent of the fen. These two com- 

 munities occur on peat often much higher above water level than even 

 mature carr, and as soon as the "deflecting factor" of cutting is removed, 

 they very rapidly become colonised by bushes and give rise to carr. It is 

 quite likely that the carr development stages we have already mentioned 

 as part of the prisere may more properly be referred to these shortened 

 successions. 



(J) Mixed sedge {Cladio-Moliiiiettmi). Vegetation in which Cladium 

 mariscus znd Molinia coeruha are more or less co-dominant has long been cut 

 by fenmen for thatch or for fuel. In it, the sedge {Chdiitm) is rather less 

 vigorous than in the pure sedge, a reflection of the influence of the 

 drier habitat upon its summer growth rates. It is scattered through 

 with Phragmites; while flowering plants such as Eiipatorium cantiabiiiuin, 

 Angelica sylvestris, Peiicedatmm palustre, Lysimachia vulgaris, Hydrocotyle 

 vulgaris and Salix repens vzr.fusca, occur sparsely throughout, though they 

 are much more conspicuous in the season following a sedge crop than 

 afterwards. 



It is clear that this vegetation has arisen by persistent cropping of the 

 vegetation, which serves to exclude bushes, but which allows continued 

 peat growth and the ingress of plants characteristic of drier habitats but 

 not susceptible to cutting. Alolinia is, of course, the most important of 

 these, for it produces annual photosynthetic shoots, and its tuberised stem 

 bases are unharmed by winter scytliing : in this, it contrasts greatly with 

 Cladiiiin, the leaves of wliich are evergreen, and the loss of wliich seriously 

 damages the plant. Bush invasion, especially by Rhamiitis frangtda, is very 

 rapid when cutting is discontinued. 



(g) Litter {Molitiietum) . When fen owners have cut the vegetation at 

 short intervals, such as one year, the sedge has been rapidly killed out. 

 The Mohnietum, thus formed, like the Cladio-Mohnietum, contains much 

 Phragmites. In it, however, Carex panicea and Junciis ohtusiflortis are sub- 

 dominant, and several smaller plants, encouraged by the removal of taller 

 dominants, also appear. These include Succisa pratensis, Thalictriimflainiifi, 

 Cirsiiiin anglicutu, Valeriana dioica, and Orchis iiicarnata. The yearly crops 

 of litter are used for cattle-bedding or for coarse chaff; the straight 

 boundaries of the litter communities coincide with the limits of different 

 owners' plots, and betray their origin. 



DBA 4 



