Hedgehope School pupils started visiting the forest in 2009 when Pat and Derek Turnbull owned the farm it sits on.
The 29ha of forest is protected by a QEII National Trust covenant.
It became known as Sherwood Forest after a Turnbull family member, who loved Robin Hood, started calling it that.
Nowadays Grant and Irene Given own the farm and it was a very special place, Mr Withington said.
"It's a rare alluvial floodplain forest."
"The trees in there are hundreds of years old, like big mātai and kahikatea.
"Beautiful old established trees."
It was in 2019 when the pupils started working towards earning their green-gold EnviroSchools award working with Environment Southland senior education adviser Josh Sullivan that the project took off, Mr Withington said.
Hokonui Runanga member Rodney Trainor also helped out.
The pupils laid trap lines in the bush and he estimated about a 100 predators including hedgehogs, ferrets and rats had been eradicated from the area.
The increase in birdlife in the bush was "through the roof" .
"We have noticed a huge increase in bird life, with piwakawaka regularly following us on our walks, tūī exploding through the forest, and kereru swooping between branches."
The pupils also worked with QEII National Trust regional representative Jesse Bythell to source seeds from the area.
"We bring them back to our frost house back at school and we germinate and grow and then we've been replanting."
Recently cameras in the area caught images of fallow deer in the bush.
The deer were nibbling on plastic plant protectors and the plants.
"The kids are very upset with that."
In the early days, all of the pupils would go to the forest, but as the school roll grew large group visits have been restricted.
However, most Fridays when possible the school’s enviroleaders walk the trap line and do the work that needs to be done.
They then reported back to the rest of the pupils about each trip.
The forest provided a rich learning opportunity for the pupils, Mr Withington said.
It sparked questions that lead to research as well as literacy and numeracy activities.
Sometimes if the carcasses of the dead predators were fresh enough they would be dissected to study what was inside.
The pupils also made videos describing their work in the bush called "Sherwood Sharp" which was their version of the news programme Seven Sharp.
