Preliminary Findings and Methods of Measuring Differences in Wood Coloration as a Result of Girdling Eastern Black Walnut

—Eastern black walnut (Juglans nigra L.) is often planted at spacings that require pre-commercial thinning. These thinnings are deemed pre-commercial due to the small diameter of the trees and the low ratio of dark wood to light wood (i.e. heartwood to sapwood). As a consequence of size and wood quality, these thinnings are often an expense rather than a source of revenue. In an effort to increase the value of these thinnings it would be beneficial to increase the ratio of dark wood to light wood. One way to increase the amount of dark wood is through costly processing using steam. However, several non-scientific studies have reported that dark wood can be increased by girdling small trees and allowing them to remain on the stump for a limited period of time. This study was designed to explore this idea. In a black walnut plantation scheduled for thinning, ten trees were randomly selected and doublegirdled. At that time, increment cores were taken 30.5 cm above the top girdle. These trees were allowed to remain on the stump for 22 months before they were harvested. Following their harvest the trees were sawn in half to reveal both the dark and light wood over the length of the log. This study found that in seven of the nine logs sampled there was a slight increase in the proportion of dark wood to total wood. However, a t-test failed to identify any differences from samples taken prior to girdling. Further, it was visually evident that none of the seven logs with increases showed a consistent change throughout the length of the log, and therefore it is not likely that girdling will improve the marketability of the log or the market value of the tree. The conclusions of this study suggest that consistency in methods of sampling are required to make valid comparisons related to any movement of wood coloration within a log. For many Missouri landowners, the idea of planting eastern black walnut (Juglans nigra L.) trees for the sawlog or veneer market may seem like a poor investment, since it may take 60 to 80 years before a return is realized. From a financial perspective, the uncertainty and risk involved with a 60 to 80 year investment makes it seem somewhat tenuous. However, even though harvesting black walnut nuts can generate an intermediate cash flow, the prospect of selling marketable sawlogs or veneer is often the deciding factor for choosing black walnut for planting. In Missouri, markets for small diameter hardwood timber are being explored. By marketing smaller diameter trees, the investment period can be shortened considerably. Small diameter markets may work for native oaks (Quercus spp.); however, black walnut’s appeal in the market is due to its dark colored heartwood. Small diameter black walnut logs have a large amount of light colored sapwood in relation to the darker colored heartwood (Panshin and DeZeeuw 1980). Because of this ratio of light wood to dark wood, black walnut may be an unlikely candidate for the small diameter market. Although there are commercial methods, such as steaming (Chen and Workman 1980), that increase the amount of coloration in black walnut, these methods are often too expensive for small sawmills. The search is on for a low cost method of increasing the proportion, or amount, of dark colored wood in small diameter black walnut. The purpose of this study was to determine if girdling and leaving trees standing for a period of time would provide a cheap, effective way to increase the colored wood content in small diameter eastern black walnut trees. When the girdled tree is harvested, the light colored sapwood will theoretically have been darkened to match the color of the heartwood, thus †Economist (LDG), University of Missouri Center for Agroforestry, 203 Anheuser-Busch Natural Resources Building, Columbia, MO 65211; Senior Training Specialist (WDW), University of Missouri Center for Agroforestry; and Director (HEG), University of Missouri Center for Agroforestry. LDG is corresponding author: to contact, call (573)884-3216 or e-mail at godseyl@missouri.edu.