The sneeze-causing, water-guzzling, fire-hazard eastern redcedar is no stranger to Oklahoma.

Landowners have been fighting the seemingly never-ending war against the invasive species for years with no end in sight. Regarding water, an often-quoted figure is 30 gallons a day for how much a redcedar tree actually uses.

However, researchers in the Division of Agricultural Sciences and Natural Resources at Oklahoma State University said that number is not entirely accurate, as they measured daily water use for an entire year of 19 redcedar trees growing on upland sites in north-central Oklahoma.

"Redcedar trees can use more water than prairie vegetation because the evergreen redcedar uses water all year and has greater quantities of leaf biomass, which releases water to the atmosphere," said Rod Will, silviculture professor in OSU's Department of Natural Resource Ecology and Management.

With funding from the U.S. Geological Survey and the Oklahoma Agricultural Experiment Station, Giulia Caterina, a graduate student, and Will and Chris Zou, an assistant professor of ecohydrology, found that, on average, redcedar trees used six gallons of water per day. However, the issue is much more complicated than a single value, as water use depends on many factors.

"Water use increased with tree stem diameter, tree canopy size, air temperature and soil moisture," Will said.

For example, they found that a 12-inch-diameter tree used a maximum of 42 gallons on a day with high temperatures and ample soil moisture, but only 1 gallon on a day during a dry period in winter. In contrast, a 2-inch-diameter tree used a maximum of 7 gallons per day and a minimum of 0.2 gallons per day.

"When the water use of individual trees was scaled up to the stand level, we calculated that dense redcedar woodlands have the potential to cycle almost all incoming precipitation back to the atmosphere," Will said. "Therefore, we likely will have less water in our streams if the invasion by redcedar is allowed to continue."

And the battle continues.