Resistance Drill Tree Ring Analysis of American Sweetgum, Norway Spruce, and Pin Oak with the Application of a LOESS Regression

Background Resistance drills are a tool that can detect the differences in density of early wood and late wood in tree ring formation to determine quantity and thickness of annual rings formed by growing trees. In this paper we assessed the ability of the drill to detect tree rings from 3 species of different wood profile types: temperate ring-porous, diffuse porous, and temperate conifers. Methods Core samples and resistance drill profiles were collected from American sweetgum ( Liquidambar styraciflua L.); Norway spruce ( Picea abies [L.] H.Karst.); and Pin oak ( Quercus palustris Münchh.) as samples of these wood profile types. The total number of rings from the core samples were counted, and a LOESS regression was applied to the resistance drill profiles to detect and count the total number of annual rings. Results The results showed the resistance drill underestimated the number of annual rings in all 3 species. Conclusions Consistent with previous literature, the resistance drill was found to underestimate annual rings when compared to physical core samples. Although the LOESS regression resulted in the exclusion of several rings from the resistance drill profile, the rings size of less than 1 mm appeared to be a more impactful variable. Currently, the use of resistance drills to acquire annual tree ring measurements is acceptable at a population level for broad assessments. However, increased accuracy in the resistance drill’s ability to detect small rings and more clearly denote ring boundaries could increase the viability of this tool for individual dendrochronology.