DULUTH, Minn. (AP) - The Superior National Forest is planning four prescribed burns this fall within the Boundary Waters Canoe Area Wilderness to reduce the threat of wildfires in areas where concentrated blocks of downed timber remain 17 years after a massive windstorm tore through the area.

The 1999 storm downed millions of trees across 500,000 acres of the forest, including 350,000 within the Boundary Waters.

Forest officials said in a statement Wednesday that significant progress has been made toward completing planned prescribed burns since the storm, but a persistent threat of wildfire remains in some blowdown areas.

The prescribed burns are planned for September and October. Two will be in the Gunflint Trail area, one will be north of Ely near Prairie Portage, and one will be west of Ely near Crab Lake.