Trees are subjected to mechanical loading during their life span or face premature mortality. The strain resulting from loads intercepted by the canopy and transferred throughout the tree is of significant importance, not only for the survival of the tree, but for the safety and well-being of the human population found in close proximity. To test the function of tree orientation to an applied load, static load tests were conducted on 15 mature pin oak trees (Quercus palustris Muenchh.). We applied the static load tests to tilt the trees 0.1° from natural position. We used a digital image correlation system to map strain in the leeward, windward, and tangential roots in the root-stem transition zone. Results indicate that mean maximum strain magnitudes are similar in the leeward and windward orientations and lower on the tangential orientation. The leeward orientation experienced compressive strain, the windward orientation experienced tensile strain, and the tangential orientation had both tensile and compressive strain. This information provides the arboricultural and plant science sectors with a better understanding of how loading force moves through trees and will further enhance tree risk assessment and root zone management protocols.

Trees are subjected to mechanical stressors, induced via dynamic (wind) and static (gravitational) forces, and must properly acclimate during their lifespan or face premature mortality. Resource allocation as a stress response is vital for tree survival, and can include the shedding of woody parts, adaptive growth, hormonal signaling cascades, and the initiation of energy transfer mechanisms. The strain resulting from stress intercepted by the canopy and transferred throughout the tree is of significant importance, not only for tree survival, but for the safety and well-being of the human population found in close proximity. As trees age and adapt to stressors and an ever changing environment, material properties also change that can influence tree stability, of which arborist and tree managers should account for. To test the function of tree orientation to an applied load, static load tests were conducted on 15 mature pin oak trees (Quercus palustris Muenchh.). Static load tests were applied to tilt the trees 0.1 o from natural position to concentrate strain at the root-stem transition zone (RSTZ) and nondestructively mapped resulting strain patterns with an ARAMIS digital image correlation (DIC) system. Using bark as a surrogate for strain on the xylem, strain resulting from static loading was mapped with the DIC system from the main stem into the structural root system. Strain patterns were analyzed across the RSTZ in the leeward, tangential, and windward directions. Results indicate that mean maximum strain magnitudes are similar at the RSTZ on the leeward (0.088) and windward sides (0.090) and lower on the tangential direction (0.058). The leeward strain was comprised of 4% tensile strain and 96% compressive strain and windward strain was comprised of 95% tensile strain and 5% compressive strain. Mean maximum strain for the tangential orientation constituted 65% tensile strain and 35% compressive strain. The changes of proportional strains found on the tangential RTSZ orientation is poorly understood and often disregarded in tree biomechanical studies. This information could prove to be beneficial to the arboricultural and plant science communities to better understand how trees manage loading events and to further enhance tree risk assessment and root zone management protocols.