Using the Optical Vulnerability method to further our understanding of drought resistance in Acer rubrum and Fraxinus americana

As climate change intensifies the frequency and severity of droughts, understanding how tree species respond to water stress has become increasingly important for forest conservation and management. This study uses the optical vulnerability (OV) method as a tool for assessing xylem embolism resistance and drought tolerance in two temperate tree species with contrasting wood anatomies: Acer rubrum (red maple; diffuse porous) and Fraxinus americana (white ash; ring porous). Using dehydration experiments and OV imaging of leaves, species-specific vulnerability curves were generated to quantify percent loss of conductivity (PLC) in relation to increasing water stress, including determination of water potential at which 50% of veins had embolized (P50) and a plant would be unlikely to recover. Results highlighted significant differences in dehydration dynamics and embolism thresholds for the two tree species: diffuse porous A. rubrum exhibited slower dehydration rates but reached critical embolism thresholds at less negative water potentials (P50 = -2.06 MPa), while ring porous F. americana dehydrated rapidly yet maintained hydraulic function under more extreme drought conditions (P50 = -3.36 MPa). These findings provide new insight into how xylem structure influences drought response. The results underscore a trade-off between hydraulic safety and efficiency shaped by wood porosity, with implications for predicting species resilience under future climate scenarios.