"We've seen black bush rats the size of beer cans, which are being brought in by the rubbish, and the fruit trees we planted a few years back have been stripped by possums.
"It's obviously not just a historical problem, because the rubbish is still being dumped ," said Mrs Pawson, who found out about the rubbish and cars after buying the property.
The couple have been in contact with South Wairarapa District Council, who erected a "no-dumping" sign, but that was cut down and removed by persons unknown after a month.
The sign has since been replaced but council's group manager planning and environment, Murray Buchanan, said a long-term solution would be hard to find.
"Because of the steep slope, it's pretty much impossible to deal with.
"I went up with one of our engineers to see if we could put a barrier up to stop people throwing things off the side but it's not practical, in terms of the physicality of the area."
Mr Buchanan said police had confirmed the vehicles had all been stolen and the rubbish was a result of "lazy" people not wanting to pay the fee at the refuse station to dispose of their waste.
"Some people's idea of getting around that is going to a beautiful spot in the country and dumping their rubbish there for free."
The couple, who met while they were students at Kuranui College, have been spending their weekends planting a flax barrier along the roadside to try and deter people from throwing things over the edge.
"Yes, we could stick up fences and spend money on surveillance, but that would just move it elsewhere in the district," said Mrs Pawson.
The couple said although they did not approve of people dumping their trash in the forest, they could understand why it happened.
"Its expensive to get rid of rubbish and the refuse centre always seems to be closed.
"We want council to recognise that there's a rubbish disposal problem in the district and to do some research on what would actually work for people."
Mr Pawson's connection with the Tararua Ranges goes back to when he was 12, helping his father with search and rescues.
He said he suspected the "car-pit" was the result of one family over a long period of time, as they were all dumped in the exact same spot.
Mrs Pawson said they had looked into getting someone to remove the cars but it was beyond ordinary salvage companies, because of the terrain.
"It's a disgrace with what's happening to the environment," Mr Pawson said.