http://www.extension.umn.edu/project...02.html#walnut
Homeowners often call the Forest Resources Extension office with questions regarding their black walnut trees. Sometimes it is to ask why nothing seems to grow under them, but more often it is to ask whether or not there is anyone out there who buys them. They have heard somewhere that these trees are worth quite a bit of money. Unfortunately, this is not usually true for walnuts grown in an urban setting. Black walnut (Juglans nigra) has often been used for furniture, art, gun stocks, and other wood products because of the color, grain and ease of working with the wood. While most logs are turned into lumber, the best logs are turned into veneer. Veneer is a very thin sheet of wood that can be used to cover another species of wood or plywood to give it the appearance of another, in this case, walnut. This allows walnut looking products to be produced at a much lower cost.
Whether the walnut will be used for lumber or veneer, there are several characteristics that determine whether or not the tree is valuable for sale, including trunk diameter, height, branching and whether or not the tree is free of defects. Another concern with urban walnuts is what could possibly be in the trunk itself. An old eye screw from a hammock may be in the tree unknown to both the current owners and therefore could cause harm to the person removing the tree.
Trunk diameter is measured at 4-1/2 feet off the ground. It can be found by measuring around the circumference of the tree and dividing the circumference by 3.14. Most buyers look for trees with a diameter of more than 18 inches. A few may purchase smaller diameter trees if they are a part of a group, but those with a diameter of less than 15 inches are of relatively little value.
Tree height is also taken into consideration. Merchantable height means the trunk height from the base to the point where major branches or trunk forking begin. A buyer will look for trees that would contain logs with a merchantable height of 8-10 feet (this is especially the case for logs that may be used for veneer). In most cases more than one log is necessary for consideration by a buyer.
Tree quality is another consideration. This is measured by how free the trunk is from defects such as crookedness, branches, holes, bumps, cracks, scars, insect or disease damage and wounds. The fewer the defects, the more valuable the tree. In general, the trees with a large diameter and a long trunk free from most defects are the ones that have the greatest potential for being a valuable lumber or veneer tree.
Most trees grown in an urban setting, however, do not usually exhibit these characteristics. An urban tree doesn't have to compete with surrounding trees for light and therefore will often have a shorter trunk with many branches low to the ground. This gives the tree little if any merchantable height. Urban trees are also more likely to have been injured or subject to disease than a tree grown in the forest.
The biggest reason why most buyers will not purchase urban walnuts is the potential risk that they may contain objects imbedded in the trunk that could pose a substantial risk for injury when removing and processing the tree. If the tree is large enough for the owner to consider selling it for lumber, it could very likely have foreign object from 25-50 years ago in its trunk that the owner would have no way of knowing existed.
The last factor is the difficulty and cost of coming to harvest one or two trees in an urban setting. It often makes little economic sense for a buyer to bring a crew and equipment in to harvest the tree. Also, most urban trees grow fairly close to houses, power lines and other structures that make it difficult, expensive and time consuming to harvest.
Although walnuts are not often considered the ideal shade tree for the yard because of the chemical juglone they secrete discourages other plants growing around them; this is often their highest value to the homeowner. A large tree can provide shade, beauty and real-estate value to a home that may not be recovered by trying to sell it for lumber.