Influence of bark on the mapping of mechanical strain using digital image correlation

Stereoscopic photogrammetry digital image correlation systems (DIC) are being used to remotely measure deformation and movement in a number of industrial research programs. The incorporation of DIC into ecology, forestry or arboricultural research can help understand how trees and other plants react during static or dynamic biomechanical trials. In the case of deformation, DIC systems map strain which will help understand how a load is transferred from one section of tree to another (i.e., from a branch to the central stem). DIC often utilizes a stochastic paint speckling (contrasting black on white) to create a series of reference points that can be tracked during testing to map strain. During previous field trials, researches have elected to remove the bark and apply the paint directly on the xylem in order to have a smooth or flat surface for the application of speckling. This potentially limits the application of DIC systems only to destructive sampling. Percent strain on Quercus rubra L. stump sprouts was mapped, and no difference between the strains was found whether the bark was intact or removed, suggesting that the presence or absence of bark does not influence strain, at least in thin bark situations. As such, it is not always necessary to remove the bark, opening up the applicability of DIC systems to nondestructive testing in ecological and arboricultural research, inclusive of repeat testing over a series of months or years.