Lob trees in the wilderness

"In the days of the voyageurs, branches were cut from tall trees along the Minnesota-Ontario border, leaving the middle of the trees bare. These "lob trees" served as guideposts, helping fur traders and explorers find their way through the uncharted maze of lakes and portages. Clifford Ahlgren and Isabel Ahlgren, two of the most knowledgeable ecologists of the area, use nine native trees as lob trees for this book, an ecological history of human activity in the Quetico-Superior wilderness area."--Jacket.