(File image). Photo: 123rf
Researchers in Canterbury have found rats and possums might actually be good for our environment - kind of.
Millions of dollars have been spent trying to control wilding conifers, which out-compete native plants and animals, and suck water from our catchments..
There are fears they could cover 20 percent of land by 2030.
But a new study has found that animals New Zealanders have traditionally known as pests eat a lot of conifer seeds.
Scion invasion ecologist Tom Carlin told Checkpoint the results of the study were unexpected.
"We were surprised to find that a lot of non-native mammals in particular, along with some native insects, were eating a lot of the seeds produced annually by these conifers.
Rats and possums may be good for environment
There were three parts to the study, he explained.
In the first part, the team glued 15,000 seeds onto individual popsicle sticks and tracked those over time.
"That told us how many seeds were getting eaten," said Carlin.
In the second part, the team carried out a camera trap study which gave them some culprits and in the last part, the team replicated the study at Willowbank Wildlife Park.
"We could then compare the teeth marks from the sticks from Willowbank and those we found in the wild so we knew which species were eating the seeds."
He said rats were the main seed-eaters.
"Possums are making a difference but really it's the rodents which are going to eat the most, and ... they can eat up to 90 percent of the seed that's dropped and that depends on the environment that you're looking at.
"So if you're going into a forest where lots of mammals will live, it's that 90 percent. But in those fragile tussock habitats that we're worried about conifers invading, it's actually closer to 30, 40, 50 percent seed that gets eaten."
Rodents still 'more harm than good'
But releasing a bunch of rats into the wild was not the answer, cautioned Carlin.
He said they were "definitely more harm than good".
"I don't think we'll ever want to release more [rats]."
Carlin said this study simply demonstrated that ecology and the natural world was very complex.
"It's not a simple matter of removing one thing and it won't impact the environment, everything is interconnected, even things that have been introduced will have connections with other parts of the environment that we need to be aware of."