UF researchers find changes in forest management could produce large water yields

August 7, 2013

GAINESVILLE, Fla. — Despite a soggy summer, water supply remains a critical issue in the Sunshine State. University of Florida researchers now say that reducing plant material, or biomass, in forests could significantly increase water supplied to streams, lakes and aquifers.

Researchers with the UF Institute of Food and Agricultural Sciences made the finding by creating computer models that analyzed the effects of reduced forest biomass on regional hydrological supplies. Their results will be published in the August issue of the Journal of the American Water Resources Association.

In one 4,000-acre tract in Central Florida, the model predicted that converting a densely planted pine forest to one managed with slightly fewer trees per acre could supply an additional 400,000 to 1.6 million gallons of water per day to the regional water supply.

According to the Florida Department of Environmental Protection’s Annual Status Report on Regional Water Supply Planning, water use in the St. Johns Water Management District, where this study occurred, was about 1.3 billion gallons a day in 2010.

Matthew Cohen, study co-author and an associate professor in the UF/IFAS School of Forest Resources and Conservation, said between 70 and 100 percent of rain that falls on Florida’s forests returns to the atmosphere through evapotranspiration instead of becoming water stored in wetlands, lakes or aquifers.

During evapotranspiration, water from the sky enters the soil, is taken up by plant roots and then is released into the atmosphere through plant leaves.

By adjusting the evapotranspiration rate even slightly, for example by reducing the number of trees in the simulated forest or by introducing prescribed fire to control small shrubs and underbrush, large water yields become apparent, Cohen said.

With more than 16 million acres of forest land in Florida, forestry provided a more than $6 billion impact on the state in 2011 and supplied nearly 76,000 jobs.

To maximize profits, many private and industrial landowners densely plant pine trees. To entice growers to reduce tree densities to free up more water for the aquifer, incentives might be an option for policymakers to consider, Cohen said.

“Because there are so many people out there who would like to see more water available, if forest land owners could be paid some kind of easement compensation, known as payments for ecosystem services, then they might be willing to adopt a new management strategy that would make water available,” he said.

Daniel McLaughlin, the study’s lead author and a research assistant scientist in the School of Forest Resources and Conservation, said forestry is already one of the most water-conserving ways land can be used for profit.

“We’re just looking for opportunities to yield even more water off those lands,” he said.

The study was funded by Rayonier Corporation, a forest products company. David A. Kaplan, an assistant professor in UF’s Engineering School of Sustainable Infrastructure and Environment, is also a co-author.