38 Pasture Prohle77is 



the primary, they occur at higher elevations where land has been 

 disturbed (even 50-100 years ago) than elsewhere. This is well illus- 

 trated by a comparison of the disturbed with the undisturbed heath 

 fescue pastures (of the uplands) which have very similar altitudinal 

 limits, yet the disturbed have a more varied flora than the undisturbed. 

 Again, Vicia Cracca, Crepis virens, and Leontodon hispidus are more 

 or less common on the semi-natural untended heath pastures below 

 600' ; but have not yet been met with on the corresponding type above 

 600' ; yet they have been frequently seen on the more recently disturbed 

 and less stable permanent pastures (20-50 years down) at even 1000' ; 

 whilst Hieracium horeale, a plant not uncommonly met with on the 

 heaths below 600', but, as far as our observations go, absent from those 

 above, has once or twice been seen on old tended grasslands at 900'- 

 1000'. Trifolium repens, normally absent from the natural heath 

 pastures, has been found at 1900' on sheep tracks on Radnor Forest 

 and elsewhere under similar conditions at 1700'. 



(5) The delaying effect of grazing animals on the progress of 

 stabilisation cannot be overlooked. Smith and Crampton(i3) have 

 pointed out that but few of our grasslands are stable (in the ecological 

 sense of the word), but that the majority are migratory and tend to 

 pass into moorland or woodland types of vegetation, and that these 

 changes are delayed by the continued operation of animals. Thus 

 neglected^ "tended pastures" at the edges of woods may revert rapidly 

 to scrub without going through the more normal intermediate stages 

 of disturbed to undisturbed heath. 



It would seem probable, moreover, that the grazing factor influences 

 all the gradual stages in stabiUsation that grasslands themselves pass 

 through. 



Thus the difference between the mountain fescue pastures and the 

 undisturbed heath fescue pastures must not be regarded as only due 

 to more rigorous chmatic conditions (due to difference in altitude) ; 

 for since the latter tend to offer more favourable grazing grounds for 

 sheep, this factor of greater interference by animals may in part account 

 for the more varied flora (more backward stabiUsation) of the heath than 

 the mountain pastures. Again, on sheep walks that are very under- 

 stocked, even at comparatively low elevations, the tendency is for the 

 fescue types of grassland to pass into the Nardus types. Furthermore, 

 constant and heavy grazing on the best types of permanent grassland 

 has been shown to be, almost certainly, competent to occasion a state 



^ Very understocked. 



