The Vegetation of New Zealand
Although the communities dealt with in this chapter fall conveniently under certain heads, there are not only intermediates between them, but it is sometimes difficult to decide into what class any particular combination of plants should go. Even in a series apparently so clear-cut as artificial page 356farmlands, nature, simultaneously, or very soon, may alter the intention of the farmer by bringing in more or less weeds; indeed, the latter element not infrequently dominates the community which is then transformed from one purely artificial to one of an exotic-induced or even an indigenous-induced character, As for the communities themselves, they are generally successions, the progress of which cannot usually be predicted for certain. Even when an apparently well-established association is present over wide areas (e. g. Ulex thicket, manuka shrubland, water-cress tangle), there is no telling what may eventually come abut through the establishment of some species new to the community, or some disease attacking the dominant member. Here, then, the term community is generally used rather than one speaking more definitely of fixity.
In considering this new vegetation as a whole, one fact — surprising enough to those taught to believe in the extreme aggressiveness of what Hooker termed the "Scandinavian flora" — is the far-greater aggressiveness—in their native land—of the New Zealand indigenous species themselves. Where rain-forest or swamp-forest has been felled and artificially replaced by European pasture-plants, as detailed further on, were it not for the constant presence of the farmers grazing and browsing animals, there would be rapid reversion to forest. In fact, it is hardly going too far to declare, that were such animals entirely removed from North Island, the whole of the present "permanent pastures" would in one hundred years, or less, be well on the road once more towards dense rain-forest!
Certainly the effect of the grazing and browsing mammal cannot be overestimated. Even, a plant-covering, so persistent as Pteridium heath (as detailed further on), is constantly being turned into grassland by aid of overstocking and burning, but alone the latter does nothing. If all stock, including rabbits, were removed from the induced steppe of semi-arid Central Otago, experiment has clearly demonstrated (Cockayne, L., 1922 a: 142) that, in certain habitats, there would be a gradual return to something not unlike the primitive plant-covering, while, if suitable seeds were sown, the process of pasture-establishment would be rapid, except in the most arid and stony places (lo. cit.: 142–43).