Diamond Willow
Diamond Willow Sticks are hiking sticks developed from willow trees that have been attacked by fungus eating away at the beginning of branches.
Diamond willow is not a species of willow, but rather it is apparently the result of attack by one (Valsa sordida) or possibly more types of fungus on several species of willow (Lutz). The word "apparently" is used because, although this is the accepted explanation, Mr. Lutz is careful in his wording since he relied on evidence for this from another source (see below). From my own search of the scientific literature, I have not found a second reference to confirm or refute the fungal explanation. The article by Mr. Lutz seems to be taken as the definitive statement on the subject. Cankers, or diamonds, form as a result of the tree's response to the fungus. The diamonds are actually more like elongated ovals with pointed ends. In my observations, if one stem in a clump of willow is affected, then all of them will be. However, the neighboring clump may be completely without diamonds. As a side note, Lutz reported seeing Quaking aspen (Populus tremuloides) in Alaska that had depressions very similar to those in diamond willow.
Formation
It appears there are four or five species of willow that grow cankers in response to the fungus. The cankers seem to result from the tree "growing away from" the site of attack. This usually happens at the crotch of a branch on a larger branch or main stem. If the branch is relatively small it seems to die very quickly. If the branch is larger, it may continue to grow and the "diamond" is formed on the branch and the stem. By growing away from the fungus, it means that new layers of growth occur further and further away from the site of the fungal attack. Thus the affected area gets larger and deeper. If the tree has been affected in several places close together, then the diamonds "run into" each other. This can result in pronounced ridges if some sapwood continues to survive, or it may "strangle" the small ridge of sapwood, which then dies.
Shape
The shape of the diamonds seems to vary from one clump of willow to the next although there may be some general tendencies within a single species. Some stems will form long narrow diamonds; others will be short and wide. Usually all the diamonds on the stems in one clump will have similar growth patterns. If the new layers of sapwood do not "move back" very much each year, then the diamonds will be deep bowl or cleft shaped. These stems will be able to survive longer than those whose diamonds are flat and open.
The bark that is left over top of the diamond changes quite markedly from the bark over the living sapwood. Depending on the species of willow, the living bark is usually smoother and slightly lighter in color. The bark over the diamond usually becomes rougher and somewhat darker. It also becomes tougher and adheres much more to the underlying wood. The sapwood is white to cream in color--again depending on the species, but also on the location. The heartwood is reddish-brown. This color tends to darken with exposure to light over a number of years.
References
- H.J. Lutz, "Observation on 'diamond willow,' with Particular Reference to Its Occurrence in Alaska", The American Midland Naturalist 60(1): 176-185, 1958.