Animal modification of native vegetation: General trends in forest modification by introduced animals

[First paragraphs...]
The title of this paper is an absurd one and was chosen for this very reason. There are, in fact, no such things as general trends in forest modification by introduced animals other, perhaps, than those implied in the bald statement that animals preferentially graze or browse forest species and may eliminate some species of extreme palatability or susceptibility which, in turn, may sometimes be replaced by species of lesser palatability or greater resistance. Yet it is commonly assumed that a general trend should be discernible and describable. Thus, if a simple and ready answer cannot be given to the frequent question, "What harm do introduced animals do to the forests?", the usual reaction is that, clearly, we do not know enough about the matter and should not express any opinion until, by dint of further research, we can reply in a dozen or so words of one syllable.On the last occasion on which I was asked this question, it was by a man well skilled in grassland management. I replied by asking him if he would sum up for me, in a word or two, the effects of animal grazing on grasslands, avoiding all qualifications as to the kind and condition of the grassland, the species of grazing animal concerned and the duration and intensity of grazing, and avoiding any reference to climatic, topographic, soil, or other environmental factors? He should give me a simple answer that would hold true no matter whether the animals concerned were sheep or cattle, horses or goats, rabbits, geese, or opossums, or of these or other grazing animals in any combination, no matter what the duration or intensity of grazing, and no matter what the kind of grassland, be it ryegrass/ white clover, cocksfoot, browntop, fescue tussock, snowgrass, or even nassella tussock grassland as all these types of gassland exist throughout their full geographic ranges.