THE PLANT-LIFE OF THE HOT LAKES DISTRICT. 



The pumice substratum, notwithstanding the considerable rain- 

 fall, in many places has only permitted the establishment of a more 

 or less xerophytic vegetation, so that the commonest plant formation 

 is shrubland with Leptospermum scoparium dominant. Where there 

 is the poorest and driest soil there may be almost pure stands of 

 Dracophyllum subulatum, a shrub virtually confined to the Volcanic 

 Plateau Botanical District. A very beautiful plant with the same 

 range as the above epacrid is Gaultheria oppositifolia, which, when it 

 grows in company with G. rupestris, a species of extremely wide range, 

 gives rise to the polymorphic hybrid G. fagifolia. 



Where soil-conditions, climate, and shelter permit trees to be 

 established there is a fine taxad rain-forest. For instance, splendid 

 forest, but now much reduced in area, can be seen from the train at 

 Mamaku. 



The effect of heated ground, together with the special chemical 

 characteristics of the soil in the vicinity of hot springs, fumeroles, &c., 

 brings about both epharmonic changes in plastic species and the 

 establishment of special plant associations. Thus, the low tree or 

 tall shrub Leptospermum ericoides is changed to a prostrate shrub ; 

 yet Leucopogon fasciculatus, with usually an ecologically equivalent 

 growth-form, under identical conditions remains quite erect. Where 

 exposed to steam from a stream of hot water various pterido- 

 phytes grow with extreme luxuriance, especially Gleichenia circinata, 

 Histiopteris incisa, and Lycopodium cernuum. Certain ferns in the 

 area being considered are restricted to places where the steam is 

 especially powerful : such are Gleichenia linearis, Schizaea dichotoma, 

 Nephrolepis cordifolia, Dryopteris parasitica, and D. gongy lodes. In 

 the hot pools themselves with a maximum temperature of 75 C. 

 there is an association of Schizophyceae. 



The eruption of Mount Tarawera in 1886 led to a considerable 

 area of vegetation being buried so deeply by volcanic ash that an 

 absolutely new habitat, destitute of plant-life, was provided for 

 plant colonization. Nineteen years after the eruption the deep water- 

 courses of the steep slopes were occupied thickly, except on their 

 ridges, by Arundo conspicua and Coriaria sarmentosa (fig. 15). On the 

 flatter ground the new vegetation was extremely open. The most in- 

 teresting point is that none of the colonizing species had come any 

 distance, for all were plants of the immediate neighbourhood. On 

 Tarawera itself and the area adjacent there are multitudes of the flat 

 cushions of a variety of Raoulia australis, just as certain members 

 of the same genus, after the destruction of the tussock-grassland, 

 occupied the depleted slopes of Central Otago. A large majority 

 of these plant settlers were wind-borne, the number of species brought 

 by birds being very few. 



L. COCKAYNE. 



