Comparing water use of Paulownia tomentosa to co-occurring native species in the southern Appalachian Mountains

Native to eastern Asia, the princess tree (Paulownia tomentosa ((Thunb.) Steud.)) is shade intolerant, fast-growing, and is primarily found in areas of disturbance. While small populations exist throughout the United States, it is prevalent in southern Appalachian forests. Recent work suggests that invasive species have higher transpiration rates than co-occurring native species, and can affect watershed-scale water cycling, including evapotranspiration, water yield, timing, groundwater recharge and subsequent freshwater resource. Invasion of southern Appalachian forest by princess tree could thus affect water yield. Although little is known about princess tree water use compared to congeners, characteristics such as rapid growth, thick sapwood, and large root systems are characteristics shared with other high water-use invasive tree species. Our objective was to determine tree water use by princess tree and co-existing native tree species—sycamore (Plantanus occidentalis), red maple (Acer rubrum), flowering dogwood (Cornus florida), blackgum (Nyssa sylvatica), tulip poplar (Liriodendron tulipifera), northern red and chestnut oaks (Quercus rubra and Q. montana), and hickory species (Carya spp.). We measured tree-level sap flux density using thermal dissipation probes, and measured air temperature, vapor pressure deficit (D), precipitation, solar radiation and soil moisture in the growing season of 2018. We fit relationships to daily scaled whole-tree water use (Q, L d^-1) vs. diameter, and Q vs. D under high light and soil moisture conditions. We found that for any given diameter, Q in sycamore, red maple and tulip poplar trees was up to four time greater than Q of oak species. Princess tree Q was more comparable to the former species. An important implication of our work is that invasion by princess tree has the potential to reduce water yield of southern Appalachian forests, which supply drinking water to nearly 48.7 million people.