These peeled trees are at Indian Tree Campground in the Bitterroot National Forest, very near the route the Corps of Discovery may have followed on September 5, 1805, as they descended from the ridge now known as Lost Trail Pass, which separates the Salmon and Bitterroot River drainages. Photo: Bitterroot National Forest
Walking overland west of the Gates of the Mountains on July 19, 1805, Clark "saw where the natives had pealed the bark off the pine trees about this same season." This, Lewis reported, "the indian woman with us informs that they do to obtain the sap and soft part of the wood and bark for food." And on September 12, the second day of their toilsome journey over the Bitterroot Range from Travelers' Rest to Weippe Prairie, Clark wrote, "On this road, & particularly on this creek,"—today's Lolo Creek—"the indians have peeled a number of Pine for the under bark, which they eate at certain Seasons of the year, I am told in the Spring." The species that was favored was Pinus ponderosa, ponderosa pine. Trees could be peeled early in May, after the bitterroot was judged ready for harvest, and never before. The process was steeped in ceremony; the result was literally the first sweet taste of spring.
It was women's work. Hard work. They used sharpened juniper sticks or rib bones of elk or bison to pry heavy slabs of thick bark from each tree. Then, with slicing tools made from the horns of mountain sheep, they carefully scraped off the nutritious inner bark and ate it immediately. The treat had a brief shelf-life, because it was unpalatable after it dried out.1
It is often said that Indians ate the cambium, but that is not true, for the cambium itself is functionally just one cell thick, and overall its components divide to produce a cambial zone, which is only a few cells thick. Although it is essential to a tree's life, the cambium has no value as human food.
On its inner surface, the cambial zone generates the water-conducting cells, or xylem (ZY-lem), which, as the tree grows, expand the dead, woody center of the tree's stem, or trunk. On its other side the cambium merges into the phloem (pronounced FLO-um), or bast. About one-eighth to one quarter of an inch thick in a mature ponderosa pine, the phloem carries food between the tree's roots and crown. In spring, at the onset of the tree's new growing season, it is rich in proteins and carbohydrates, and that is why it was once valued as food. As the outer cells of the phloem deteriorate, they become the corky interior surface of the outer bark.2
Peeled trees also served as trail signs. En route back across the Bitterroot Mountains, on June 17, 1806, over deep snowbanks that hid the ground, Clark noted: "I was in front and Could only pursue the derection of the road by the trees which had been peeled by the nativs for the iner bark of which they Scrape and eate."
The peeling of ponderosa pine trees was discouraged and finally prohibited as settlers moved onto reservation lands, because it was considered injurious to trees that were valuable to them as sources of lumber for building. But since cuts such as that illustrated in the photo above did not sever the cambial zone around the whole circumference of the tree, they did no harm. In fact, a layer of cambium soon formed within the callus tissues to help heal the wound.