78 NEW ZEALAND PLANTS. 
the heath-like coprosma (C. rugosa); the whauwhaupaku (Notho- 
panax anomalum), of similar form to the coprosmas; two New 
Zealand brooms, the large-flowered broom (Carmichaelia grandiflora) 
and the swamp-broom (C. paludosa). In the shade grow the creek- 
fern (Blechnum fluviatile), the triangular hard-fern (B. vulcanicum), 
and the prickly shield-fern (Polystichum vestitum). The white-leaved 
lawyer (Rubus schmidelioides var. coloratus) climbs over the shrubs. 
Manuka shrubland has strong affinities with fern-heath, one of 
the most widespread plant-formations in New Zealand. Probably 
most of the present fern-heath has resulted from the action of man 
in burning the forest. Thus in the neighbourhood of the Marl- 
borough Sounds, in many parts, it is quite uncertain whether an 
area of burnt southern-beech forest, after the sowing of grasses, 
may not be replaced by agriculturally worthless fern-heath, the 
extermination of which is extremely difficult. 
The leading plant of the formation is the bracken-fern (Pteri- 
dium esculentum). This fern cannot grow in the forest shade; but 
as soon as forest is burnt, the spores of the fern being already in 
the ground, thousands of plants appear, and, thanks to the rapidly 
growing underground stem, full of plant-food which had been manu- 
factured by the leaves, the area in an astonishingly short time 
becomes bracken-fern, frequently many feet in height. Where the 
fern reaches its full development nothing else can grow, but usually 
some of the manuka-thicket plants of the immediate neighbourhood 
are present, while the tutu (Coriaria sarmentosa) is almost certain 
to be a constituent. The effect of overstocking with cattle on fern 
after it has been burnt is remarkable ; indeed, without their aid it 
would usually be impossible to grass the land. Were it not that a 
bracken plant-covering consists entirely of fern-leaves, and that the 
destruction by cattle of the rolled-up end of the leaf stops further 
growth of that leaf, the fern would invariably conquer. Its one 
weakness leads to its downfall. 
The weathering of rocks prepares in the talus-slope at their base 
new soil for colonization, which in part is peopled by those shrubs 
which grow on the rock, so that an open shrub-association or a 
dense scrub may eventually be formed. This is the topographical, 
not biological, succession mentioned in Chapter IJ, the rock associa- 
tion not turning into scrub by slow degrees. Nevertheless, as shrubs 
are extremely common denizens of rocks, there is a kind of relation- 
ship between the associations of the two stations. 
