AbstractSapwood may be lost due to wood decay fungi or mechanical damage. Assessing the impact of sapwood loss on the likelihood of tree failure has not been empirically tested. The purpose of this research was to determine the effect of the loss of sapwood on the flexural stiffness of tree trunks for different species and trunk sizes. Three tree species (Acer rubrum, Liquidambar styraciflua, andQuercus acutissima) were tested at two sites using pull testing techniques. A portion of the stem was mechanically removed and the trees were again pull tested. As the percent reduction in cross-sectional area increased, the percent reduction in stress to deflect trunks decreased linearly, regardless of species. Stress from sapwood loss was compared to an equivalent calculated loss in heartwood with the same cross-sectional area. The calculated loss of heartwood to cause an equivalent magnitude of stress was almost twice as large as cut area of sapwood. Trees were also tested by pulling in opposite directions with respect to sapwood loss. The percentage reduction in stress was greater for trees tested in compression.