FORAGE CROPS, MEADOWS AND PASTURES 1^69 



which do not naturally contribute to the flora of a well marked type of 

 grassland. 



e) Exotic species, which are not indigenous in a district. 



The number of primary species on most types of grassland is not 

 considerable. When a field long under arable cultivation is put down to 

 grass the primary species are usualh^ late to come in ; this is particularly 

 true of Bromus credits, Molinia caerulea, Nardus sfricta, Triodia decumbens 

 and Festitca ovina ; and if they come in early, they do not rapidly make 

 their contribution to the herbage, i.e. they may fall below their minimum 

 or exceed their maximum figmes. Primary species which sometimes 

 come in early are frequently met with as arable weeds, such as Poa tri- 

 vialis and Festuca nihra at lower elevations and on the better soils, and 

 Agrostis vulgaris on the poorer soils. 



The various stages in the process of stabilisation of semi-natural 

 grassland — through tended to untended and thence into natural t3^pes — 

 may be summarised thus : 



At 20-30 years, under the influence of periodic manuring and compa- 

 ratively heavy grazing with cattle and sheep the secondary species {Cy- 

 nosurus cristatus, Trifoliiim repens, Plantago lanceolata etc) are still abun- 

 dantly represented ; the primarj^ species {Agrostis vtdgaris, Festuca ovina 

 and the heath herbs) are, however, beginning to take a prominent plac^ 

 in the herbage. 



At 50-100 3'ears the primary- species have gained considerably but do 

 not yet stand in their normal relation to each other ; the secondary' species 

 aie much reduced. 



After 100 years the influence of the original disturbance and of manur- 

 ing is now finally lost ; the grazing is generally by sheep only, the nett 

 result being that the primary species have completely suppressed the se- 

 condary species. 



The relation of primary and secondary species to their commercial 

 and sown counterparts is as follows : 



a) The commercial seed does not appreciably^ hasten the appearance 

 nor add to the contribution of the desired plant. This is true of sowing 

 Festuca ovina or other fine leaved fescues and is, in many cases, equally 

 true of Anthoxanthum odoratnm ; the inclusion of such seeds in mixtures 

 is not justified economically. It is far from certain that the commercial 

 Trijolium repens seed produces a lasting plant, as on many soils phosphatic 

 manure is all that is necessar}- to hasten the appearance of the indigenous 

 plant. 



b) The commercial seed may produce a great bulk of the required 

 plant in the earh- years of a Ic}' (far more than the indigenous species would 

 attain to naturally at any time). The behaviour of Lolinm peremie sown 

 on good soils is an excellent example. Under these circumstances good 

 seedings of the commercial seed is economically justified, especiall}^ if hay 

 is required in the early years of the lej-. 



c) The commercial seed may hasten the appearance of the desired 

 plant and cause it to bulk somewhat more largely in the early )'ears of a 



