Fire and Emergency New Zealand is investigating the cause of the blaze which occurred about 2.30pm yesterday at the bike tracks behind Logan Park High School.
He rushed to get a fire extinguisher out of his car but by then flames were shooting up and the blaze was too fierce for him to put out himself.
Firefighters arrived quickly and extinguished the flames, which by then were large, producing billowing smoke.
Mr Seaton said it was "unfortunate" the tractor was written off, especially as the group was working hard on new projects.
It was creating a new children’s track around the car park, a public road up to the tracks and building a car park and toilets.
He hoped the cost would be mostly covered by insurance.