The Vegetation of New Zealand
3. General conclusions
3. General conclusions.
In order to pave the way for the concluding part of this work it is advisable to state briefly some conclusions derived from the details given in this chapter.
The flora of New Zealand, notwithstanding its strong endemism, possesses two very distinct elements not floristic only but ecological. page 417 The first, and, as I believe, the more primitive, is not one simple floristic entity, but consists of a combination of the palaeozelandic and subantarctic elements of the flora, now difficult to disentangle. They have this one property in common, the power, for the most part to endure a fair amount of cold. In other words, the element is a temperate one.
The second element, also largely endemic, consists of descendents of an ancient palaeotropic stock, so ancient indeed that endemic genera have been developed (Rhabdothamnus, Ixerba, Alectryon &c.), as well as many distinct endemic species.
Yet notwithstanding this great age of the members, and their long isolation far from the tropics, but few have become really fitted to the present average climate of New Zealand, in fact the majority can tolerate very little frost. For the most part, the species of this class are confined to the lowlands, and in the south some are only found near the coast. This element, in fact, is eminently subtropical; so that the present-day climate is one to which it is not perfectly attuned. Should a change of climate occour, then with increase of temperature the palaeotropic element would advance southwards and the palaeozelandic-subantarctic retreat to the mountains, while, with increase of cold, the contrary would be the case. The isolated colonies of Nothofagus truncata, north of lat. 37°, point to such a change of climate, while the presence of the tree-fern (Hemitelia Smithii) in the Lord Auckland district suggests a warmer period. But apart from speculations, the non-toleration of frost by so many New Zealand species is good evidence that there has either been a considerable northern land-extension during the glacial period or else that such did not owe its origin even, in part, to increase of cold.
It has been shown that while there is a considerable Australian element, it is made up largely of Subantarctic and Palaeotropic species, while the true Australian element does not play a conspicuous part in the vegatation. Especially is the absence of characteristic Australian genera noteworthy, e. g. Eucalyptus, Acacia &c., although virtually all the Tasmanian species are not only quite hardy in the warmer parts of New Zealand, but some can spread spontaneously. Bearing these facts in mind, the possibility of direct land-connection with Eastern Australia except at a very remote period cannot be entertained.