Saltcedar water use: Realistic and unrealistic expectations

Saltcedar (Tamarix spp.) is a widespread invasive plant found in riparian corridors and floodplains in 16 western states. In addition to being associated with such problems as increased soil salinity and decreased plant diversity, saltcedar has been reported to be a prolific water user. Popular press articles widely report that each individual saltcedar tree can use as much as 757 L (200 gallons) per day. Consequently massive control and removal efforts are underway to reduce transpirational water loss and increase water salvage for arid and semiarid environments. Although the potential economic benefits of these control efforts are touted, it has not been proven whether such water savings are possible on a stream level. The original citation for the 757-L estimate does not list the experimental design or techniques used to arrive at this value. We use three lines of evidence - peer-reviewed scientific literature, sap flux rates and sap wood area, and potential evaporation rates - to demonstrate the improbability that saltcedar, or any other woody species, can use this much water per tree on a daily basis. A more realistic estimate of maximum tree-level daily water use derived from sap flux measurements would be < 122 L·d^-1 (32.2 gallons). Estimates of water salvage would be grossly overestimated using the popular water use value (757 L·d ^-1), and economic benefits from saltcedar control based solely on water salvage are questionable.