Forestry Tasmania has admitted it accidentally logged an area of the Weilangta State Forest which was reserved as a habitat for a threatened species of parrot.

The company says a mapping error was to blame.

Greens Senator Bob Brown says it is a shameful piece of illegal logging and claims the error has further eroded the habitat of the rare and endangered swift parrot.

He says Forestry Tasmania management has broken its own rules and he is calling for severe penalties.

"A job should be at stake on this," he said. "Otherwise these breaches of Forestry Tasmania's rules will continue to occur.

"They've happened in the past. This is by no means the first time. This is glaringly bad. It shows a failure of management."