R. G. Stapledon and T. J. Jenkin 37 



(2) The more stable grasslands, i.e. those which have probably 

 not been under cultivation in historical memory, are colonised by 

 relatively few species ; whilst on pastures down no longer than about 

 20 years the number of contributing species is considerable. 



Thus the end stage in stabihsation of grasslands is reached when 

 the few most enduring species have suppressed the larger number of 

 less successful ones. 



Plants may therefore be considered as primary indigenous species 

 when they colonise land which has never been disturbed or which has 

 become completely re-stabihsed ; the number of such plants (in so far 

 as grassland is concerned) is relatively few. Examples are, Molinia 

 caerulea and Nardus stricta and Juncus squarrosus on moorland and 

 allied grasslands. Festuca ovina, Agrostis vulgaris, Triodia decunibens, 

 and AnOioxanthum odoratum (as a distributed plant), with Galium 

 saxalile and Potentilla erect a and other herbs on the Welsh hills. Bromus 

 erectus, Festuca rubra var., Lathyrus pratensis and Galium verum^ on the 

 Cotswolds. Agrostis alba et vars., and to a slight extent possibly also 

 Lolium perenne, Poa spp., Cynosurus cristatus, Anthoxanthum odoratum 

 and Festuca rubra on certain old lowland permanent grasslands. (See 

 Paragraph 5, hereunder.) 



(3) Plants are secondary indigenous species when they appear 

 (by themselves without sowing) on disturbed land. In a sense these 

 plants are followers of man. They tend to come in on land that has 

 been ploughed, very heavily manured, or even heavily grazed by 

 stock near a homestead. The effect of disturbance has presumably 

 been to upset the equihbrium between habit and primary species in 

 a manner favourable to the secondary species which are no longer 

 suppressed by their primary competitors. The secondary indigenous 

 species may furthermore persist for a generation even after man has 

 entirely withdrawn his attention. Most of the ordinary herbage 

 plants^ are secondary species on the majority of tended grasslands, 

 several being confined to definite types, and all showing a decided 

 quantitative relation to habitat; and thus, in conjunction with the 

 primary species, they give a definite character to the various types 

 of semi-natural grassland. 



(4) The altitudinal limit of a species depends largely on competitive 

 interaction ; and since the secondary species are finally suppressed by 



^ Also a locally prominent plant on some of the Radnorshire hills. 

 - The valuable grasses and clovers of the Agricultural text books, and the miscellaneous 

 plants of tended grasslands. 



