Video: Leaf Area Index and Forest Water Yield, Matt Cohen, WWALS Webinar 2026-05-28

Reducing forest cover to about what it was before the 1990s would increase water yield and could be seen as restoration of more natural forests.

That was one take on the WWALS Webinar by Dr. Matthew J. Cohen, presenting research about forest management to lower Leaf Area Index (LAI) and increase water yield, on May 28, 2026, from noon to 1 PM.

Video: Leaf Area Index and Forest Water Yield, Dr. Matthew Cohen, WWALS Webinar 2026-05-28

Leaf area index (the ratio of leaf cover to ground area) increased in the 1990s. Reverting to about the LAI before then would increase water yield into streams and wetlands, and thence into the Floridan Aquifer. This works by reducing evapotranspiration from the trees.

LAI can be decreased through means such as delaying replanting after clearcutting, not planting as densely, and thinning more or sooner. The resulting increased waterflow is as clean as any source.

Unlike the agriculture that is the subject of the Basin Management Action Plans (BMAPs), forestry does not irrigate.

The research is quite thorough and Dr. Cohen indicated more potential effects.

Here is the zoom video:

https://youtu.be/_PTxZJ6BJFw

Suwannee Riverkeeper John S. Quarterman mentioned WWALS and introduced Hailey Hall.

Suwannee Riverkeeper John S. Quarterman, 2026-05-28 –jsq for WWALS

WWALS Events Committee member Hailey Hall gave a brief introduction of the speaker.

Hailey Hall –WWALS Events Committee Member, 2026-05-28 –jsq for WWALS

Dr. Cohen spoke for about an hour.

Matt Cohen, 2026-05-28 –jsq for WWALS

There were some questions and answers during the talk, and more at the end, about potential flooding, does reduced evapotranspiration reduce rainfall, and surface water into groundwater.

At about 1:08:30 Dr. Cohen notes that you can’t put water into the aquifer through a well unless you remove the color from tannic-acid-colored water By an FDEP interpretation, probably of state law. See for example U.S. EPA, Unknown Date, Summary of Florida’s Water Reuse Guideline or Regulation for Environmental Restoration.

A loophole is that a natural recharge such as Brooks Sink are exempt to the color issue. So it’s curious that the July 2025 map of Water First North Florida (WFNF) recharge wetlands shown by SRWMD staff seems to show those wetlands near known natural sinks.

WATER FIRST NORTH FLORIDA, 2025-07-08 –SRWMD Staff
PDF

Also, there are apparently known ways to remove the color.

Dr. Cohen reminded us that he had mentioned to SRWMD that decreasing LAI as above could increase recharge by about 50 million gallons per day (mgd), which is more than the 40 mgd that WFNF promises.

Jodi Boas started a discussion of incentives and how to keep them from being perverse.

Jodi Boas, 2026-05-28 –jsq for WWALS

Incentives could instead be used to keep land in trees, instead of selling of forest land for subdivisions and parking lots. There would have to be contractual provisions about that in any LAI-reduction subsidy incentives program. Other things to worry about include would reducing LAI result in less timber being sold and sawmills being closed. Of course, mills are already closing for other reasons, including hurricane damage.

Matthew J. Cohen is the Carl S. Swisher Chair in Water Resources at the Water Institute of the University of Florida, and the Director of the Institute.

Dr. Cohen is a Professor in the School of Forest, Fisheries, and Geomatics Sciences. He is an ecohydrologist with nearly 20 years of experience addressing water resource and ecosystem science challenges in Florida and around the world. Dr. Cohen received his PhD from the University of Florida in 2003 and joined the faculty in 2006. He has led research focused on hydrological restoration of the Everglades and Big Cypress, the changing ecological state of Florida’s springs, the deep links between forests and water, and the changing patterns of Arctic and Antarctic stream functions. This work has been funded by the National Science Foundation, the Department of Energy, all five Water Management Districts and the Department of Environmental Protections, and the US Army Corps of Engineers, and has resulted in over 120 publications.

For other WWALS Webinars, see:
https://wwals.net/about/wwals-webinars/

They are usually on the second or third Thursday of the month, from noon to 1PM. After a brief introduction, the speaker has about 45 minutes, with the remaining time for questions and answers and discussion.

They are recorded, so if you miss one, you can see it later on YouTube. Here’s a WWALS video playlist:
https://youtube.com/playlist?list=PLKwQ5xfKf-QxWRGrV9iExlyXQIVnzOtPX&si=0Atnjwrm_ikyV-sh

WWALS Webinars are organized by the WWALS Events Committee; maybe you’d like to join that committee and help.

For more WWALS outings and events as they are posted, see the WWALS outings web page, https://wwals.net/outings/. WWALS members also get an upcoming list in the Tannin Times newsletter.

About WWALS: Since June 2012, WWALS Watershed Coalition, Inc. (WWALS) is an IRS 501(c)(3) nonprofit charity working for a healthy watershed with clean, swimmable, fishable, drinkable water.

Mission: WWALS advocates for conservation and stewardship of the surface waters and groundwater of the Suwannee River Basin and Estuary, in south Georgia and north Florida, among them the Withlacoochee, Willacoochee, Alapaha, Little, Santa Fe, and Suwannee River watersheds, through education, awareness, environmental monitoring, and citizen activities.

Our Watershed: The 10,000-square-mile WWALS territory includes the Suwannee River from the Okefenokee Swamp to the Gulf of Mexico, plus the Suwannee River Estuary, and tributaries such as the Withlacoochee and Alapaha Rivers as far north as Cordele in Georgia, as well as parts of the Floridan Aquifer, which is the primary water source for drinking, agriculture, and industry for millions of Georgia and Florida residents.

Suwannee Riverkeeper: Since December 2016, WWALS is the WATERKEEPER® Alliance Member for the Suwannee River Basin and Estuary as Suwannee RIVERKEEPER®, which is a project and a staff position of WWALS focusing on our advocacy.

Contact: John S. Quarterman, Suwannee RIVERKEEPER®
850-290-2350
wwalswatershed@gmail.com

You can help with clean, swimmable, fishable, drinkable, water in the 10,000-square-mile Suwannee River Basin in Florida and Georgia by becoming a WWALS member today!
https://wwals.net/donations