Cockayne. — Plants- of Chatham Island. 313 



important effects of five upon the vegetation of Chatham 

 Island : — 



(1.) Small plants which in the original formation are pre- 

 vented from spreading get a foothold, and at first, at any 

 rate, form a much larger proportion of the vegetation than 

 formerly. 



(2.) The ground, being exposed to wind and sun, gets drier 

 on the surface, and so becomes occupied by plants which 

 could not thrive so well on the wetter ground, consequently 

 the plants of the wetter ground become fewer in number. 

 Thus repeated burnings substitute Dracophyllum paiudoswm, 

 for Olearia semidentata, while at the same time Gleichenia 

 circinata and Pteris esculenta increase in quantity. 



(3.) The ground being cleared of vegetation allows the 

 inroad of grazing animals, which consolidate the ground and 

 feed upon certain plants, which consequently decrease, while 

 others untouched will increase. This leads finally to the 

 destruction of certain plants altogether, such as Phormium 

 tenax, as before mentioned. On the other hand, the Uncinia 

 is not touched at all by stock, and it increases very con- 

 siderably, especially on the outskirts of forests ; but Pteris 

 esculenta increases most of all. 



(4.) One or two burnings may make very little change 

 indeed in the vegetation of a bog, so that after a lapse of 

 many years it is quite impossible to tell whether such a 

 formation has been burnt at all ; and it is, moreover, very 

 likely that the early changes after a first or even a second 

 fire may not be permanent, and that the original formation 

 may be to all intents and purposes reproduced. But this, 

 I fancy, will depend a good deal upon the number of grazing 

 animals in the neighbourhood, while their influence is regu- 

 lated by the nature of the soil. Thus some pure Sphagnum 

 formations are too boggy for sheep, which, however, can walk 

 with safety on the soil of any of the other formations Many 

 places are quite inaccessible to cattle, and still more so to 

 horses. 



Before concluding this section I must again emphasize the 

 fact that, in considering the changes which have taken place 

 in the vegetation of any region since the advent of man, it 

 is conjointly and not separately that the influence of exotic 

 plants, introduced animals, and fire must be considered. 



History of the Vegetation of the Chatham Islands. 



I do not intend to discuss at any length the history of the 

 vegetation of the Chatham Islands, and the affinities between 

 its species and those of other parts of the New Zealand area. 

 A comparison of the species common to New Zealand and the 

 Chatham Islands, detailing exactly any differences, however 



