In an island so small as Chatham Island, where herbivorous animals have roamed almost everywhere at their own sweet will ever since their first introduction, and where, moreover, much of the vegetation has been burnt again and again, hardly any of the plant-covering can still be in its virgin condition. On this account the plant-formations may be divided into the recent, or modified, and the original, or
unmodified. From a careful study of the present plant-covering in a large number of places it seems certainly possible in many instances to get a fairly accurate idea of the original formations, especially when aided by the information of those who have resided on the island almost from its first settlement by Europeans. Those small pieces of original vegetation which from their peculiar situation have up to the present been undisturbed also aid most notably in affording a clue to the character of similar formations in other parts of the island; but, of course, the results deduced from such a comparison must be accepted with caution, since a slight difference in edaphic conditions may lead to more or less considerable changes in a formation. In some instances the descriptions of the individual plant-formations which follow are limited to certain stated localities.
Dr. H. C. Cowles very justly observes (142, p. 178) that “plant societies must be grouped according to origins and relationships, and the idea of constant change must be strongly emphasized”; and, further, “The laws that govern changes are mainly physiographic; whether we have broad flood plains, xerophytic hills, or undrained swamps depends on the past and present of the ever-changing topography.” The above ideas I have attempted to in some small degree carry out, and have taken for the most part the plant-formations in what seems to me their order of sequence, and have sought in some instances to point out their relationships. To have attempted, however, a physiographical classification of the formations with any degree of thoroughness was out of the question. Such would require, in the first place, to be based on what does not yet exist—a description of the topographical geology of the island by a competent geologist; and, in the second place, a very much more accurate study of the formations than I was able to make would be essential.
There are on Chatham Island two distinct regions of vegetation, of which the most marked difference is shown by the forests. The one is confined to the tableland, and the other comprises all the remainder of the island. For this latter I suggest the name “lowland region,” a not particularly good name, but sufficiently applicable, since most of its surface is only a few metres above sea-level, while its hills are low isolated volcanic cones. Probably some of the differences between the vegetation of the tableland and lowland regions have been accentuated by fires, &c., while the woods above the north-west and west coast of the southern part of the island seem, so far as a rapid examination showed, to be in some degree a transition between lowland and tableland forest. All the same, the differences between the
vegetation of the two regions is sufficiently well marked, and that such should occur on two adjacent parts of a very small island is a matter of considerable interest.