With the state entering its fourth year of drought, some conservationists are looking at thinning Sierra forests to increase the amount of water that flows into area rivers.
The Nature Conservancy issued a report Friday that argues that thinning forests on public lands can reduce wildfire risk in the Northern Sierra. The report also found that such action brings a bonus: water conservation.
Thinning dense forests may lead to a 3 percent to 6 percent increase in mean annual stream flow to some watersheds, according to the report.
The conservancy based its estimates of stream flow on gauge records across 11 watersheds from 1980 to 2000 and found that the Feather River watershed would show the greatest increased water flow due to thinning.
This not the first time tree thinning has been examined for water conservation. However, the conservancy report is one of the first to look into the effect that ecologically based forest thinning would have on water yields in the Sierra Nevada and the economic benefit that could come from it.
Several studies have shown that tree density in the Sierra is higher now than in the past.
The conservancy report contends that such densely packed forests are trapping snow at the tops of trees. Forest thinning would allow the snow to settle on the ground as snowpack.
The report also estimates that higher water yields would provide a potential economic benefit to water agencies and hydropower operators, said Kristen Podolak, ecologist and lead author of the report.
As more water flows downstream after thinning, the expectation is that hydropower plants and utilities would use additional funds created by the increased water flow to partially or completely fund the expense of forest thinning, which is done by the U.S. Forest Service.
The report looked at 150 published studies and matched that information to what would happen if the Forest Service met its goal of increasing forest thinning activity threefold, Podolak said.
The forest service’s goal is to thin 500,000 acres per year across California. However, it has not met that goal because of costs, legal and administrative issues, Podolak said.
In the study, the conservancy looked at 11 watersheds in the Northern Sierra representing 1 million acres.
About 20 percent of that area can be treated by forest thinning, Podolak said.
To calculate the increased economic benefit from thinning, the conservancy surveyed hydropower plants in each watershed.
“We priced out the power generation, agricultural water use and municipal water use at market values from the literature and obtained the total benefits that thinning would generate in each watershed,” said Bruce Aylward, economist with Eco System Economics, an environmental consultant and study co-author.
That analysis showed that the biggest economic benefit would be reaped by the Feather and American rivers.
It is unclear how the cost of thinning will be paid, especially since it may be years before any water benefit is seen.
A recent Forest Service analysis of Northern California found that the cost of thinning some forests runs from $1,000 to about $15,000 per acre.
When paying for the cost of cutting trees, size matters, said Jeffrey Fried, a Forest Service research forester.
“If you put a cap of 21 inches, then a lot of stands can be treated effectively and most of those can pay for themselves,” Fried said. “People recommending cutting down trees less than 10 inches in diameter – those trees are rarely merchantable.”
In its report, the conservancy based its findings on the kinds of thinning the Forest Service is doing under ecological forestry guidelines. However, trees less than 20 inches in diameter are the size of trees the conservancy focused on in the study, said David Edelson, Sierra Nevada project director for the conservancy.
The conservancy believes that increased water yields can allow for payment of tree thinning. And is some cases, that cost could be borne by utility ratepayers, Edelson said.
“We’d like to create a mechanism by which all the beneficiaries of forest management could contribute a share of the funding to undertake thinning activity,” Edelson said. “This could be from a combination of federal funding, or it could come from state funding under the water bond. Or it could come from private investors like hydropower and water utilities.”
Edelson cited Denver’s Forest to Faucets project as an example of how ratepayers contributed to a headwater program that involved forest management.
That program was a partnership between Denver Water and the U.S. Forest Service.
In that plan, the Denver Water utility matched the service’s $16.5 million investment, for a project cost totaling $33 million. Those costs went toward forest treatment and watershed protection projects spread out over five years.
In 2010, Flagstaff, Ariz., passed a $10 million bond issue to be used for forest service watershed activity, Edelson said.
“The water utilities are beginning to see the importance of headwaters in terms of downstream water supply,” he said.
On Friday, the Association of California Water Agencies also released its own report that calls for better headwater and forest management – and for better collaboration among federal, state and other agencies, and other stakeholders.
“The idea is to collaborate with the Nature Conservancy and the Forest Service and the Sierra Nevada Conservancy on this ecological thinning idea, and see how we can do it in a way that is ecologically responsible,” said Dave Bolland, project manager at ACWA.
“This proactive forest management approach anticipates catastrophic future impacts and tries to address them,” Bolland said.
Call The Bee’s Edward Ortiz, (916) 321-1071. Follow him on Twitter @edwardortiz.