Displacement and Replacement, 289 
Certain species of Acaena, too, will greatly increase in amount. In wettish 
parts or shady slopes-of montane and subalpine steppe, Chrysobactron Hookeri 
or its var. angustıfolia will form extensive colonies and, in some localities, 
Celmisia spectabilis will. become dominant. 
The most interesting case is the transformation of steppe into induced- 
desert. This has happened in Central Otago and is happening on the Mackenzie 
Plains and in parts of the North-eastern botanical district. Central Ötago, 
especially below an altitude of 600 m, possesses a very dry climate, owing to 
the ranges to the W. S. and E. robbing the clouds of most of their moisture. 
Under a cloudless sky insolation is powerful and the summer hot, so that the 
district is admirably suited for the growing of peaches, apricots &c. At Clyde, 
altitude 201 m, the average rainfall is some 38 cm. The rock is schist and the 
soil light, soft and extremely fertile. In the early days of settlement, both river- 
valleys and hill-slopes were covered with a continuous mantle of tussocks and their 
accompanying plants, but it must be pointed out the climate was always arid, as 
evidenced by the strongly xerophytic character of much of the florula *) and the 
rocks weathered by wind. For more than 60 years, sheep have been depastured on 
the area and during much of that time there have also been millions of rabbits. 
Year by year, too, as much of the tussock, as the sheep-farmer was able to burn, 
he burned. Atthe present time, as far as the eye can reach, in many places, not a 
tussock is to be seen, the general aspect is that of naked Eon hills not unlike 
giant dunes. But there are certain plants present, all the same, and, even yet, a 
considerable number of sheep and innumerable rabbits hold their own, thanks 
to the presence of the introduced Rumer Acetosella and Erodium Cicutarium 
and the fact that at above 700 m altitude there is abundance of vegetation ’). 
Continual burning leads finally to the death of the tussock, bare patches of 
ground become exposed to the wind which whirls the surface-soil high into 
the air in black clouds. Heavy rain, when it occurs, first of all makes tiny 
runnels into the soft soil which, converging, form eventually a powerful stream 
that cuts by degrees a deep trench several metres in depth. As the surface- 
soil blows away, the stony ground beneath is exposed and this is, in time, 
captured by the low cushions of Raoulia lutescens (Plate LXV, Fig. 94, 95) 
and the circular mats of R. australis and R. Beawerdii, all normally river-bed 
Species absent from steppe. Other indigenous species, rare in the original 
association, enter in, especially the tiny .grass Poa maniototo and the matted 
Siellaria gracilenta as also introduced species especially Urzica dioica, Erodium 
ı) The following may be specially mentioned: — Carex resectans, Colobanthus brevisepalus, 
Acamma Buchanani, Carmichaelia Petriei, C. compacta, Hymenanthera dentata var. alfina, Pimelea 
sericeo-villosa, P. sericea, Myosotis pygmaea var., Raoulia Parkii, R. Beauverdü. 
2) The climate there Be wetter, it is not so easy to burn the tussock (oa er or 
Danthonia Aavescens). At lower levels, the difference between sunny and sheltered slopes is 
2. the former being at nie and the latter more or less occupied by X. Fe 
and certain introduced annuals. 
Cockayne, The Vegetation of New Zealand. : S 19. 
