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1. General.

So many areas throughout New Zealand are insufficiently explored, or altogether unknown, so far as plant-distribution is concerned, that few statements as to the range of any species are absolutely valid. Therefore, the classification proposed in this chapter is advanced with some hesitation and offered merely as a more or less provisional attempt to deal with a subject that will be treated with much greater precision by some investigator in the future. Nevertheless the classification, first put forth by me in 1914, has been tested in the field and modified from time to time, so that is may be asserted with some confidence that the botanical divisions are fairly natural and appear to serve the purpose for which they were first designed. Yet in most cases it is not feasible to fix definite boundaries to the various botanical districts; for not only is there a gradual merging of one into another, but local climates, or edaphic conditions, occur which permit the occasional presence of species, or indeed associations, not in keeping with the general florula, or vegetation.

The major divisions of the region are here designated botanical provinces. These are based largely upon climatic change depending on latitude. As before six provinces are admitted. Except with regard to junction of the Central and Southern provinces all seems simple. For fixing the southern boundary of the Central Province two courses are open. The first is to restrict the Province to North Island — a very convenient arrangement, admirable for most purposes but hardly natural. The second course is to extend the Province to South Island and to let it include that portion of South Island lowland vegetation which comes very close to that of the southern part of the Ruahine-Cook district, but to exclude all the adjacent high-mountain vegetation. This course is followed here, the main objections page 379to its adoption are, (1.) that the three northern botanical districts of South Island will each belong to parts of two provinces and (2.) that the southern boundary must be ill-defined and its position always open to discussion. But these objections seem slight in comparison with separating into two classes vegetation and florulas so similar as those of the forest and coastline of all the Sounds-Nelson, much of the North-western and part of the North-eastern districts.

In dealing with the botanical provinces — subject to the explanation in the last paragraph — the ground is fairly secure for their basis is the stable one of gradual change in species in proceeding from north to south. But, when the question of smaller subdivisions, here called botanical districts, comes in, the ground is much less stable, not merely because new discoveries of species, or of distribution, may become disturbing factors, but because facts of various kinds — floristic, ecological and geological — have to be considered.