Possums devour more than 21,000 hectares of forest every night in New Zealand, but far from indiscriminate gluttony, it seems they’re looking for the most protein-rich leaves.
Instead of grazing on a different tree every night, the invasive brushtail possums (Trichosurus vulpecula) will often systematically strip a particular tree over several nights before moving to another, causing eventual dieback in the tree.
Studying possums in New Zealand, scientists from the Australian National University looked at protein in kāmahi, toro, rimu, hīnau and māhoe growing in the Tararua Range, and found a direct link between higher protein and the amount of possum damage.
They found just a tiny increase in available nitrogen concentration in leaves—from 0.3 per cent to 0.5 per cent—resulted in almost a 20 per cent increase in the likelihood that the tree would suffer heavy damage from possum browsing. They also found a species could vary hugely—some kāmahi trees had 17 times less protein than others on the same mountain range.