Dunedin Botanic Garden collections supervisor Dylan Norfield said many of the city’s deciduous trees still had leaves on them, despite being three weeks into winter.
"I’ve noticed it, especially the trees alongside the [University of Otago] Central Library, and I’ve never seen it like that there before.
"They’re still very green."
The trees outside the library are Italian alders (Alnus cordata), and Mr Dylan said they were known to hold their leaves late.
"But not this late.
"They should be bare now, definitely."
He believed warm soil temperatures around the city were causing some deciduous trees into responding as if it was not yet winter.
"It’s only been recently that we’ve actually had frosts and cold enough temperatures to help those leaves drop.
"So I would expect the leaves to start dropping quite quickly now.
"It’s certainly been a later onset of winter than we would have expected."
Mr Norfield believed the leaves might have stayed on the trees longer than usual because they were near a prominent light source.
The Italian alders were next to the Central Library, where lights were on late into the night.
"I have seen that happen in the United Kingdom, but it should only cause a slight delay in them dropping their leaves."
The warming climate was the main cause of the phenomenon, he said.
"Autumn seems to be coming later and we’re getting warm spells during winter. "So we’re going to continue to get the odd plant that is completely out of sync.
"It’s certainly causing some confusion in them."
