westcountrybuddha asked why the possums were being kept out of the trees in the parks. well, the answer is that they were too sucessful - there were so many possums that the trees were suffering and so some of them (trees not possums) have wide metal collars around the trunks to prevent the possums from climbing up and committing great depredation. in new zealand they have become a real environmental problem.
the same thing happened with fruit bats about 5 years ago - they were having a fabulous knees up in the botanic gardens and completely destroying the trees. so they were moved first to the fitzroy gardens and then to yarra bend. soon they will be visiting my fig tree for light snacks.
there are still enough trees for a sustainable possum population and you can often see them in the evenings. this little possum was lying on the grass as i walked through the park a few weeks ago.