Art. XXXVIII.—On the natural Spread of the Eucalyptus in the Karaka District.
[Read before the Auckland Institute, 17th September, 1883.]
Mr. Wallace in summing up his interesting chapter on “The Flora of New Zealand: its affinities and probable origin” (Island Life), points out the remarkable fact that compared with the European, few Australian plants have succeeded in establishing themselves in New Zealand, but it must be borne in mind that there has been a continued stream of imported seed from Europe, affording repeated opportunities for the introduction and establishment of the naturalized plants.
As nearly all the species which are identical and peculiar to New Zealand and Australia, are either temperate or alpine forms, Mr. Wallace fairly concludes that there has been an interchange of species in comparatively recent times.
In accounting for the absence of such characteristic Australian genera as Eucalyptus, Acacia, Hakea, etc., he says:—“In this particular case, however, we have some very remarkable evidence of their non-adaptation.” The evidence of their non-adaptability to spread and run wild in New Zealand, consisted in there being no record of the fact. I need hardly point out how local causes—not always apparent—influence the natural spread of most plants; even the hardly Ulex europæsus is not exempt. In my own district, although there are some old-established hedges, I have only observed two self-sown seedlings of Hakea acicularis; yet Mr. T. F. Cheeseman, F.L.S., says that it “has established itself over several miles of open manuka country at the foot of the Waitakerei ranges, and is increasing fast.”* In regard to the Acacias, several species readily establish themselves in most districts; the allied Albizzia lophantha competes successfully against, and in time destroys, almost the strongest vegetation met with in open country.
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To have hastily placed on record the apparent naturalization of so important a genus as the Eucalyptus, would have been an error; however, now that its adaptability to spread naturally is fairly established, the fact is worth recording. In pastures, or lands where the native vegetation has been almost entirely destroyed, the gum spreads freely; on a neighbouring farm, whore they have not been checked, there are about 5,000 self-sown plants from a few inches to 15 or more feet in height—scattered more or less about; the largest of the dense patches—1/5 acre—contains over 300 young trees.
[Footnote] * Trans. N.Z. Inst., vol. xv., p. 291.
Probably many seeds germinate through being trodden in by the stock; at the same time numbers of seedlings must be annually destroyed from the same cause; many obtain protection from clumps of Pomaderris and manuka. On another farm about 500 gum-seedlings have been transplanted from the pastures and waste-lands this season. Compared with the grass-lands, the young gum-trees springing up amongst the indigenous vegetation—as might be expected—are scarce; yet they are sufficiently numerous to make it appear not improbable that, if allowed their freedom, in the course of time they would spread over the more favourable portions of the district. Although the seedlings naturally stand a better chance in the struggle for life amongst the dwarf vegetation, those that germinate amongst the stronger manuka, once they attain the level of their taller rivals, compete successfully with the surrounding vegetation. When not too dense gum-seeds will germinate and grow amongst manuka four feet or more in height. The seeds appear not to be widely disseminated, the furthest plant yet observed, from the supposed parent-tree, being 98 yards to the eastward. In the vicinity of four gum-trees—the remains of two homesteads deserted upwards of 25 years ago—numerous young plants have sprung up amongst the furze and manuka. It would have been interesting to have watched the annual increase, but, unfortunately many of them have been destroyed by fire, or carted away by settlers. In another part of the district, some of the self-sown seedlings, growing amongst the indigenous vegetation, have attained a height of 31 feet. The greater portion of the young plants are seedlings of Eucalyptus globulus, this species being the most numerous; but interspersed amongst them are seedlings of E. piperita, rostrata, hæmastoma, etc.
Grum-trees in this country produce fertile seed in less than ten years; some will attain a girth of 9 feet 1 inch, and many a height of about 80 feet in 27 years.
I have not had the opportunity of personally observing to what extent the Eucalyptus has spread in other districts, but I am told that at Waiuku the seedlings are “coming up in crowds” near some old trees. In this case, however, the native vegetation has been destroyed by fire. The common E. globulus appears to spread most freely; but as it is not improbable that some of the more valuable Australian timber-trees may spread with equal freedom, considering their rapid growth and that they are rarely destroyed by stock, the fact may not be without some value in regard to our future forests.