A team of army and forestry officials unearthed the illegal encroachment in a remote section of the park near Ban Dan Mek in the Sam Ran subdistrict of Sam Chai district.
The team, led by Col Chakardpong Hongthong, deputy commander of 6th Calvary Regiment, and Sam Chai district chief Kanok Srichainan, discovered felled trees and bare stumps left along a 20-km. village road leading to Ban Dan Mek.
Col Chakardpong admitted he was shocked that such a vast swath of the national park had been invaded. He believes the encroachment is being done by investors and politicians intent on exploiting 50-100 rai of public land to build private homes and rubber or cassava plantations.
Some influential investors, he said, illegally established demarcation posts on, and claimed ownership of, public land in the middle of the Phu Phan mountain range, with each plot stretching 300-500 rai. More than 10,000 rai of park have been destroyed, Col Chakardpong estimated.
Mr Kanok said local authorities faced difficulties solving the problem due to a lack of staff.
"We've continuously checked and arrested the offenders, but encroachment remains rampant," Mr Kanok said. "Another problem is that the encroachers are among the "powers-that-be" in Kalasin and neighbouring Udon Thani. There are both local politicians and government officials involved."
Kalasin's provincial peacekeeping force will work with administrative and forest officials and other agencies to take legal action against encroachers, he said. He also pledged that authorities would reclaim the public land and implement rehabilitation programmes.
The Phu Phan National Park inspection was taken as part of the National Council for Peace and Order's promised crackdown on forest encroachment nationwide.