The order sending him back to his old office was dated Oct 25 and signed by Thanya Netithammakul, director-general of the National Parks, Wildlife and Plant Conservation Department.
Surachai Thathes was appointed acting chief of Thansadet National Park on Jan 16. He will resume duty as a forestry expert at the office of the 5th Conservation Area in Nakhon Si Thammarat.
He has been replaced as acting chief by Uthen Saengmukda, from the office of the 4th Conservation Area.
A source at the department said Mr Surachai was demoted because he failed to investigate forest encroachment on Koh Phangan, or take legal action against the culprits.
On Oct 19 a combined team of park officials and soldiers from the 45th Military Circle examined a forest area near Ban Thong Nang in tambon Ban Tai in Koh Phangan district after receiving a complaint that the area had been logged.
Photographs of tree stumps and felled timber in the area had also been posted on social media.
The team found 17 tree stumps of 1 to 1.5 metres in diameter, a quantity of processed wood and many tree trunks.