The Possum – a Forest Pest?

by John McNab
We shall be doing a great service to the country in stocking these large areas with this valuable and harmless animal. 
So said the Auckland Acclimatisation Society’s Annual Report 1917, about possums.
But possums have become branded as a pest particularly by the Department of Conservation and Forest and Bird.
The ‘hate speech’ by these two organisations has amounted to propaganda. Typical was the claim by DOC and Forest and Bird that there were 70 million possums and that they were destroying forests.
Similarly the claim of possums preying on birds and nests has been a myth. Possums are herbivores not carnivores. In the mid-1990s a Department of Conservation workshop was held with the title of “Possums as Conservation Pests”.
A senior scientist Graham Nugent of Landcare Research, spoke on the subject.                 
Assuming the oft-quoted figure of 70 million possums in New Zealand, the marsupials  “apparently consume about 21,000 tonnes of vegetation per day – presumably 300 g wet weight consumption multiplied by 70 million possums,” he said. “This oft-quoted figure is frequently used to depict possum as a rapacious consumer of all things green.”
“But,” added Graham Nugent. “that implication ignores the trees’ daily foliage production of 300,000 tonnes for forests alone  – 7.5 million hectares x 15 tonnes wet weight of foliage per hectare per year.”
Simply the fictitious number of 70 million possums would browse only about 1/15th or 7 percent of the new foliage each night.
Besides most possums live near margins of forests adjoining paddocks rather than in the forest and a significant part of their diet is grass or spring and summer growth on farm trees like willows, growing outside the forest.
Graham Nugent termed the 70 million possum figure by DOC as a “back-of-a-cigarette-packet” calculation.  If one took a more realistic figure of perhaps 10 million rather than 70 million possums they would consume just one per cent, of the daily foliage production.
Graham Nugent went on to say that possums do not threaten the total national forests by deforestation. For the bulk of New Zealand’s forest, the process is one of a change in individual species known as composition. There would be less of palatable vegetation species. So the change is merely a structural forest change.

Note our own school-yard experiments on possums show they do not touch eggs, even when tempted with attractants. You can see the four-fold steps we undertook here, here, here, and here.
We strongly encourage anyone interested in the outcome to repeat the experiments for themselves – we did ours in such a way as other potential intruders such as rats and mice were excluded.

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