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[Read before the Auckland Institute, 26th September, 1910.]
On the 19th July, 1896, I read before the Auckland Institute a paper in which I attempted to trace the principal causes which are combining to produce the extensive and rapid disappearance of our native forest. This was followed in 1898 by another, in which I endeavoured to forecast what will be the future condition of the forest when something like a balance shall have supervened between the destructive agents on the one hand and the resilient powers of nature on the other. It may be well to follow up the subject a stage further, and try to point out some of the more notable effects which are already following on the deforestation of the country, and which, as time goes on, must increase in an accelerating degree.
In order to present the matter as clearly as possible I shall recapitulate once more the argument of the first paper :—
The two principal destructive agents, besides the axe of the bushman, are cattle and fires. Any one of these acting alone is sufficient to do a great deal of damage; but when they all act in conjunction—as they generally do—the destruction is greatly accelerated and intensified.
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The greater part of the forest below a moderate altitude, throughout both Islands, is an open cattle and pig run in which by the browsing, trampling, and rooting of the animals the undergrowth is gradually destroyed, the surface-roots lacerated, and the soil trodden into mud, which in summer hardens almost into a bed of concrete. The consequence is that the larger trees, deprived of their accustomed nourishment and protection, gradually grow thin and open at the top; the ground is covered with the fallen leaves, and the débris of centuries, now exposed to the sun and wind, is dried to tinder, when the whole place is ready to be swept by fire, which sooner or later is sure to happen.
In thickly settled districts, and in those where timber-getting is carried on, the destruction is, of course, most rapid and complete, as every clearing, timber-working, and road-line forms a starting-point for the fires, which spread into and kill some portion of the standing bush. And as wherever the fire has once passed it will pass again while there is anything to burn, before very long, in districts where clearings are frequent, the whole bush is consumed, with the exception, perhaps, of that which stands in the lower and damper situations, or which from the conformation of the country is protected from the sweep of the flames. In this way, in a comparatively few years, immense areas have been destroyed in many of the more settled districts, while in others the work is going on more or less rapidly and completely, according to the nature of the bush and the climatic and other conditions.
Now, it does not require a great deal of intelligence to understand that such a radical alteration in the conditions of the country as is involved in this wholesale destruction must result in very serious consequences, whether for better or for worse. So far, unfortunately, I think it must be admitted, the consequences are very largely for the worse—as I shall endeavour to show.
The effects of the disappearance of the New Zealand bush may be roughly classed under two heads—viz., climatic and topographical.