Effects of drought on water use of seven tree species from four genera growing in a bottomland hardwood forest

For floodplain forests such as bottomland hardwood forests, large fluctuations in moisture availability can lead to stress from both flooded as well as drought conditions. Likewise, these forests can be diverse in species composition and the water use and drought strategies of co-occurring species will impact surrounding hydrology, nutrient dynamics and productivity. Therefore, the objectives of this study were to compare water use, canopy stomatal conductance and its response to environmental drivers in co-occurring bottomland hardwood species from four genera (Carya, Fraxinus, Quercus, Ulmus) during a drought and average rainfall year. Water use was similar across years in cherrybark oak and winged elm. For swamp chestnut oak, willow oak and shagbark hickory water use was about two thirds in the drought year compared with the average rainfall year and in American elm and green ash it was about one half. Species also varied in their responses of water use to VPD, reference canopy stomatal conductance values, and the timing of leaf senescence during the drought and average rainfall year which will impact ecosystem processes based on drought conditions and species composition. Shagbark hickory, winged elm and swamp chestnut oak exhibited the most declines in water use due to soil saturation. In general, species exhibited a tradeoff between flood tolerance and drought tolerance as well as between maximal water use potential and drought tolerance. In total, differences in water use and its response to environmental drivers during drought and non-drought years for bottomland hardwood forests will depend on species composition and these findings can benefit modeling efforts in temperate floodplain forests.