86 NEW ZEALAND PLANTS. 
available. Then, all of a sudden, the advance of the great tree- 
community is stopped; and from this point, except at those areas 
mentioned in Chapter IV, the brown tussock extends to the east 
coast, its ranks unbroken, save by swamp, or scrub, or river-bed, 
or dune. 
In the North Island the formation is much more local, its main 
habitat being the lofty pumice tableland in the centre of the North 
Island and the adjacent mountain-slopes. 
The great tussock - grassland plant-community falls into two 
distinct classes, according to the conditions the dominant tussocks 
and their companion plants can and cannot tolerate—the relative 
amounts of light, of rain, and of the degree of “sourness” of the 
soil being perhaps the determining factors. Where the soil is 
specially “ sour,” the rainfall fairly heavy, and cloudy skies frequent, 
the red-tussock (Danthonia Raoul var. rubra*) dominates; but 
where the climate is drier—often very dry indeed—the soil well 
drained, and sunny days abundant, one or the other of two tussocks 
—the silver-tussock (Poa caespitosa) or the hard-tussock (Festuca 
novae-zealandiae)—is the physiognomic plant. As the Danthoma is a 
much taller tussock than either of the other two, the two plant- 
formations may be known as “fall tussock-grassland”’ and “ low 
tussock-grassland ”’ respectively. 
Low tussock-grassland (fig. 13) is found, in the South Island, 
on the east of the Dividing Range, beginning at the eastern margin 
of the western subalpine or montane forest, from Nelson to the 
northern part of the Fiord Botanical District inclusive. The forma- 
tion ascends from sea-level to about 4,000 feet altitude, but its 
altitudinal limit depends altogether upon the aspect of the slope, 
one facing north permitting it to climb very much higher than one 
facing south. These limitations concern only the plant-formation 
and not the tussocks themselves, or many of the accompanying 
plants, for, having joined other associations, they ascend into the 
alpine belt. 
The plant-formation consists of two well-defined plant-associations. 
In one the silver-tussock (Poa caespitosa) is the dominant tussock ; 
it may be called the “ silver-tussock association.” In the other 
*The “type” of Danthonia Raoulii is the tall tussock-grass of Banks 
Peninsula, and not the red-tussock, though elsewhere the latter is by far the 
commoner plant. 
