The trucks belonged to Christchurch company Treetech, which was assisting with storm recovery at the park.
In a statement, Treetech chief executive Chris Walsh said it would be devastating for the team if the trucks had been set on fire intentionally.
"It's about a million dollars worth of damage, but we're pulling out all the stops to keep going."
Walsh said he was raised in Invercargill and started his climbing career in Queens Park, so the area was dear to his heart.
Gear would arrive from other depots in the coming days so they could get back up and running, he said.
Detective Sergeant John Kean, of Invercargill, said it appeared the four vehicles were deliberately set alight.
"Thankfully no one was injured," he said.
Invercargill City Council manager parks and recreation Caroline Rain said the incident happened at the park's maintenance yard and confirmed the area was now a crime investigation scene.
"We are still assessing the extent of the damage to the trucks and surrounding property, and working with Treetech on the next steps forward.
"This incident is incredibly disappointing, especially given the tireless work of our staff and contractors in recent weeks to ensure the trees in our parks and reserves were made safe for the community following October’s storm."
On Wednesday morning, the site was cordoned off by a gate and emergency tape.
It was not clear how the incident would affect recovery, which included reopening the remaining closed part of the park, Rain said.
Queens Park suffered major damage when strong winds toppled trees in October.
Walsh believed the opening of Coronation Drive in Queens Park by Christmas may no longer be possible
Two fire investigators are working alongside Police.
- LDR is local body journalism co-funded by RNZ and NZ On Air
