CARNIVORA 93 



several of the Central Otago ranges, as on the spurs of the Rough Ridge 

 and the Morven Hills districts. The northern slopes of the spurs are almost, 

 in many instances entirely, bare of grass, while the southern shaded slopes 

 still carry a fair amount of pasture. The grass covering generally stops 

 abruptly at the bottoms of the valleys, even when these are not worn into 

 water-channels. The vastly greater depletion of the pasture on the northern 

 slopes is easy enough to understand. They are more exposed to the sun 

 and to the frequent violent parching north-west winds; they lose their 

 covering of snow earlier in spring than the southern slopes, and are thus 

 more closely grazed at a critical season for the pasture; and sheep at all 

 times show a preference for feeding on the warmer sunny slopes. When 

 the pasture on the exposed slopes fails, that on the shaded slopes has to 

 feed all the stock that is about, and unless the stocking is reduced to meet 

 the new conditions the remaining grasses are sooner or later eaten out. 

 The desert, with all its problems, is then established. 



In this account of how the desert conditions have arisen, Mr Petrie 

 refers only to sheep, because it is the loss in sheep-carrying capacity 

 which is so serious, but later on, after describing a typical specimen 

 of the country, and showing that in inaccessible situations a con- 

 siderable variety of fairly vigorous grasses live on, he adds : 



" This is one of the facts that go to indicate that the extermination of the 

 grasses in this desert country is mainly due to eating out by overstocking, 

 rabbits as well as sheep being included among the stock carried." "The 

 desert and the greatly denuded lands are not wholly destitute of vegetation. 

 In most of their lower areas greyish, flattened, firm, nearly circular patches 

 of scab- weed (Raoulia australis and R. lutescens) are thickly dotted about the 

 bare ground. Though otherwise useless, these moss-like composite plants 

 help to keep the soil from being blown or washed away, and when old 

 supply, in the decayed centres of the patches, spots with some amount 

 of humus where grass-seeds can more readily settle and grow." 



These plants are never eaten either by sheep or rabbits. 



In regard to their effect on other native species of plants Mr 

 Petrie writes to me in a letter of ist May, 1916: 



I know that rabbits have done much to reduce the abundance of the 

 Otago Spear-grasses (Adphylla squarrosa and A. Colensoi chiefly), probably 

 during times when the ground was covered by snow. When I first visited 

 inland Otago (1874) Adphylla Colensoi was most abundant. In riding about 

 it was almost impossible to deviate from well beaten tracks or roads, because 

 the spines pricked the horses' legs and feet. I know of no evidence that 

 sheep would eat fairly full-grown Adphylla leaves, but young plants must 

 be more or less eaten both by sheep and cattle (as well as by rabbits). 

 Several species of Celmisia, notably C. densiflora, have been greatly checked, 

 and C. densiflora almost exterminated. 



Dr Cockayne is now (1921) engaged on an exhaustive investigation. 

 Captain F. W. Hutton writing me on 23rd March, 1892, said: 

 As to the extermination of the Wild Spaniards (Adphylla} , I believe 



