WAUSAU, Wis. (AP) — The heavy snowfall in Wisconsin this winter has led to a boost in the number of snowmobile registrations. The Department of Natural Resources says registrations are up in many north-central Wisconsin counties. Nearly 229,000 riders have registered snowmobiles this year. That's 4,000 more than last year, but still behind the record 235,000 set four years ago. Many trails opened in December and have stayed open, thanks to steady snowfall and cold temperatures. DNR spokeswoman Joanne Haas says it's not surprising that Wisconsin is such a popular snowmobiling destination with its 25,000 miles of groomed trails. Vilas County leads the about 10,600 snowmobile registrations, 300 more than last year. Marathon County has about 8,800 registrations.