Responses to water stress were measured for sugar maple (Acer saccharum subsp. saccharum Marshall) sources from Oklahoma (Caddo sugar maple), Missouri, Tennessee, Ontario and a black maple (Acer saccharum subsp. nigrum F. Michx.) source from Iowa. Seedling sources were selected for differences in temperature and precipitation of their geographic origins. Seedlings were preconditioned through moist (watered daily) or dry (watered every 4-7 days) cycles and then exposed to prolonged water stress. Dry preconditioned sugar maple seedlings from Oklahoma, Missouri, and Tennessee, sources from warmer and/or drier climates with greater relative evapotranspiration potentials, declined less rapidly in net photosynthesis, stomatal conductance, and water use efficiency (WUE) as water stress increased than dry preconditioned seedlings from Ontario and Iowa having origins in cooler, moister climates. Under imposed water stress the Ontario and Iowa sourced seedlings increased their root to shoot ratios and decreased their specific leaf area, mechanisms for drought avoidance. However, no corresponding changes in these values occurred for Oklahoma, Missouri, and Tennessee sources. Results from this study suggest greater tolerance of water stress in the Oklahoma, Missouri and Tennessee ecotypes from the western and southern range of sugar maple resulted primarily with WUE rather than other water stress coping mechanisms.