Thinning for Water in California: Various Disciplines Weigh In

Sediment basin for KREW (KIng’s River Experimental Watershed) from SNAMP website.

M of T noted in a comment that a force against MT (mechanical treatments) which may be necessary before PB (prescribed burns) is the problem of dealing with non-commercial material that needs to be removed. Her comment reminded me of this article in The Economist.

Thinning efforts are off to a great start but must accelerate, says Timothy Quinn, head of the Association of California Water Agencies. Five times as much forest should be thinned every year, estimates Roger Bales, a hydrologist at the University of California, Merced. To find out how much extra water a thinned watershed produces, the university has placed sensors in thinned and control plots in the Stanislaus-Tuolumne Experimental Forest north of Yosemite National Park. Depending on landscape and precipitation, thinned areas shed 10-40% more water into streams, Mr Bales estimates.

More accurate numbers will be available next year. The hope, says Eric Knapp, a Forest Service ecologist in Redding, is that a new thinning technique will prove to produce even more water when flow volumes from next spring’s snowmelt are known. Some plots are not thinned evenly, but rather by clear-cutting gaps with a diameter one or two times the height of surrounding trees. The idea is to clear an area big enough for a good snowpack to form, but small enough for shade to reduce evaporation and extend the melting season.

California’s governor recently signed a bill that facilitates thinning watersheds. But some environmentalists resist “cutting any tree for any reason”, as the Forest Service’s Mr Murphy puts it. And some think thinning doesn’t produce meaningfully more run-off. That’s the opinion of Chris Frissell of Frissell & Raven Hydrobiological and Landscape Sciences, a consultancy in Polson, Montana. Thinning has become popular in the state, but, he says, it disturbs soil, generating silt that harms aquatic life.

Clearing trees with fire is cheap if all goes to plan but only makes sense in certain areas. Thinning with big chainsaws on wheels can cost up to $650,000 per square mile. This could be recouped with timber revenue if big trees are felled. But the chainsaws are usually only let loose on smaller trees, so taxpayers must cough up.

One solution would be to get water utilities or hydropower producers to fund the thinning. AMP Insights, a consultancy which has estimated the value of water flowing out of the Sierra Nevada, reckons the extra flow would defray the cost of removing trees by 20% and, in wet years, by 60% or more.

Here we have one scientist (Bales) with monitors in plots saying that thinned areas get more water into streams, but (Frissell) possibly at the expense of aquatic life. We’ll explore that in greater depth in the future.

As Brian Hawthorne said earlier, thinning for fuel treatment is not the only reason to thin. Brian also mentioned restoration. Bales and others are thinking about dealing with climate change and water resources, another purpose, involving more disciplines. The scientists in the article come from a variety of disciplines.
Here’s Eric Knapp, forest ecologist.
Tim Murphy is a hydrologist/soil scientist (according to LinkedIn)
Chris Frissell seems to also be a scientist at U of Montana in addition to the consultancy the article mentions. Here’s his information. He is an aquatic ecologist.
Roger Bales works on water and climate engineering and is a professor at U of Calif Merced. Here’s his info.


  1. No mention of restoring a more resilient set of species compositions, which would probably mean cutting more flammable incense cedars and white firs, favoring the fire resistant ponderosa pines, clumps of sugar pines, and room for California black oaks to flourish.

    I suspect that there will continue to be slow progress in thinning, due to political ‘fiddling’. The government doesn’t even see all the barriers…. yet.

  2. That’s going to be some REALLY expensive water. I see several problems:
    (1) Thinning will produce only modest/temporary changes in water yield;
    (2) Thinning must be accomplished over large areas to be meaningful;
    (3) Changes in water yield will be temporary and therefore treatments must be repeated (there’s no way the repeated treatments pay for themselves, even if the first treatments does pay a little);
    (4) The secondary effects on wildlife and water quality and carbon storage will be significant, especially if more roads are to be built;
    (5) Thinning might make fire hazard worse, because logging produces lots of hazardous slash, makes the forest hotter/dryer/windier, and stimulates the growth of ladder fuels.

    • 1) I think we can generally agree, here.

      2) Only if water production is your only goal. Yes, thinning-from-below has been shown to have multiple benefits, far beyond just water conservation.

      3) No, not repeated. Prescribed fire helps maintain water flows but, forest health is an important idea to tend and nurture. Ecologists care little about forest health, welcoming all kinds of wildfires (and not just ‘natural’ ignitions).

      4) When you compare intensely-burned landscapes to properly-thinned forests, I do think that those three items are much better in thinned forests. New roads are rarely built, here in California.

      5) Clearly, this is where the wheels fall off, Here in California, “whole tree yarding” takes the slash out of those forests. The idea that thinned forests are more flammable is just ridiculous and wrong. Thinned forests did just fine when California Indians expertly used controlled fires over very large areas. When forests were less dense, were dry forests ‘drier’, even though there is, normally, no rain at all, during the summers? Were those forests unnaturally windy, due to human practices? Finally, the reduction of ladder fuels stimulates more ladder fuels?!?

      It seems pretty clear that current thinning practices are good for California forests, and free-range wildfires are not. The extremists of today WANT “larger and more intense wildfires”. They insist that “thinning is worse for our forests than wildfires”. ‘Bizarro World’, indeed!

  3. 2nd- with all due respect I don’t think you know (1) for the area in California. (2) I think people are talking about large areas of thinning/PB.
    (3) for trees to grow up to the same size (and thence using the same water) mayl take (what 80 years, Larry probably knows). 80 years is a long time.
    (4) you don’t really know that. Carbon is another question entirely and not without disagreements.
    (5) not if it’s designed and carried out to improve fuel conditions.

    • (3) Some of the theorized gains would, no doubt, be ‘siphoned’ away in multiple ways. The remaining forest trees will take advantage of the now-abundant water and put on a burst of growth (and water uptake). Old springs might, temporarily, regenerate. Some brush would likely, temporarily, thrive. Bearclover would also likely expand its influence. None of those things are really bad things in the ‘big picture’.

      An 80 year old vigorous pine tree looks a lot like ‘old growth’ to the untrained eye. Remember, too, that 30+” diameter trees are ALL protected, unless they are hazard trees.

  4. Way back in the mid to late 1990s R4 did a lot of serious study and, if memory serves, even did some small test treatments on the Wasatch-Cache. The effort was short lived. No guesses as to why.

    • A test was tried near Wright’s Lake, on the Eldorado NF. Long and narrow clearcuts were installed, with different compass alignments, to see if snowpacks could be increased, without tree canopies in the way. I don’t know what the outcome was but, a side effect was discovered after a wind storm blew through, causing so much blowdown. Those clearcut corridors in the red fir zone became wind tunnels. More recently, that area burned in the Freds Fire.

        • Larry, I heard about that too in Wyoming.. it came up from time to time. I think it was clearcutting though, and was a non starter socio-politically or at least that was the FS thinking (if we can’t get logs out for sawmills a direct benefit that you can see, how can we do it for something you can’t see).
          Others who remember this are invited to chime in.

          The difference to my way of thinking is that there are a variety of good reasons to thin and prescribed burn, to treat fuels to protect species and communities, to give firefighters places to work, to change species composition to (historic and/or more fire resilient), to protect watersheds. It’s just another reason to do thinning and PB especially where water is scarce or expensive.

  5. Following the logic that reducing density(thinning) stimulates streamflow…, does this mean clearcutting maximises streamflow? Or is there a break point, after which more thinning results in less streamflow?

    • Good question, Fergus! I don’t know but I bet there are studies out there.. I remember in the 70’s folks were doing things like that at Hubbard Brook in NH. I think for our purposes today clearcutting is out but they studied it and alternatives I’m sure.

  6. A 2015 paper from The Nature Conservancy, “Estimating the WATER SUPPLY BENEFITS from Forest Restoration in the Northern Sierra Nevada” (emphasis not mine) states that:

    “Using syntheses of over 150 studies on the relationship between forest harvest and water yield, we estimated the potential water yield impacts from mechanical thinning to restore a forest’s ability to store snow and use water more efficiently. Our analysis suggests that, if the current scale of forest restoration is increased three-fold, there could be up to a 6 percent increase in the mean annual streamflow for individual watersheds. In the Feather River, the watershed with the greatest area available for thinning, we estimated thinning might produce ~97,000–285,000 acre feet of additional runoff. We used a cost-benefit analysis to compare the costs associated with this increased pace of forest restoration to the economic value of water supply benefits to downstream hydropower, agricultural, and urban water users. We found that the economic benefits from increased hydropower generation and water uses are sufficient to cover between one-third and the full cost of thinning, assuming a low or high water response to forest thinning.”

    Mechanical thinning, not clearcutting. The authors write that they “did not estimate differences in water yield due to combined thinning and prescribed fire.” The benefits to water supplies might be greater than with thinning alone.

  7. More commodity production mentality. The Forest Service is required to manage national forests for what is ecologically sustainable. Where thinning is needed to produce that, it may make sense for those who benefit economically to help pay for the thinning. However, one of the beneficiaries could include aquatic ecosystems and species if they have been affected by overcrowded forests that reduced streamflow. (There might be some interesting questions about who owns water that the national forests have been using to grow too many trees.)

    • No, I don’t think the FS is required to “manage forests for ecological sustainability”. Otherwise, would we ever have a ski area, a microwave tower, a gas well or pipeline, a dam or water pipeline, or (even the much maligned) coal mines.
      … If there is an “ecological primacy” concept it’s not in statutes… the first I heard of it was in drafts of the 2000 planning rule.

      • 36 CFR 219.8: “The plan must provide for social,
        economic, and ecological sustainability
        within Forest Service authority and
        consistent with the inherent capability
        of the plan area, as follows:
        (a) Ecological sustainability. (1)
        Ecosystem Integrity. The plan must
        include plan components, including
        standards or guidelines, to maintain or
        restore the ecological integrity of
        terrestrial and aquatic ecosystems and
        watersheds in the plan area, including
        plan components to maintain or restore
        structure, function, composition, and
        connectivity …”
        My only answer to your question is that the requirement applies to ecosystems and watersheds, which can be defined by the Forest Service so that parts of them can be sacrifice areas, as long as the whole meets the regulatory requirement. Nothing says “primacy,” but there are ecological limits.

        • That’s the 2012 planning regs, not the statute (NFMA)..

          You said “The Forest Service is required to manage national forests for what is ecologically sustainable.” If some areas can be “sacrifice areas” but the whole needs to be “sustainable” and that involves “restoring” or “maintaining” things as they were .. The key question is still “what are you going to restore?” “to which of previous conditions”? Why (and beyond “it’s good for the ecosystem by definition”)? And is it possible to make time’s arrow go backward given all the changes, including climate change? (Most people would say “of course not”).

          It hasn’t been tested in court but it would be interesting to see serious high-powered attorneys deal with this, say, when the FS tries to revoke dam or ski area permits because those do not “promote ecological integrity” and thereby violate the 2012 Planning Rule.

          • You said, “I don’t think the FS is required to “manage forests for ecological sustainability”. I hope you are not saying that the FS is not required to follow federal regulations (which here represent its interpretation of the law). Legally adopted regulations have the force of law.

            There is no requirement that individual projects promote ecological integrity. The 2012 Planning Rule applies only to forest plans. A forest plan that allows large-scale destruction could be invalidated because it violates regulatory requirements for ecological integrity.
            Projects can always be rejected as inconsistent with forest plan requirements for ecological integrity. (When forest plans are revised, they must address existing facilities and ongoing permits – 36 CFR §215(a).)

  8. I believe that in parts of Utah and perhaps some other states, tree harvest (clearcutting at the time – 1980s and maybe even earlier than that), was done primarily to provide water flows. There were many experimental forests established that conducted watershed studies – the HJ Andrews in Oregon, Coweeta, Hubbard Brook. There is some very interesting newer work by Susan Dickerson-Lange looking at the conditions in the PNW that favor snow retention and snow melt. In some places, openings are more important to retain snow and in other places high canopy closure is more important. It depends on the winter temperatures. In some places, the heat of the tree boles helps the snow melt faster under a canopy vs. out in the open. I think that the focus is generally on retaining moisture on the site by slowing down melt and not increasing stream flows – you generally have to cut a fairly large area and keep thinning over time to maintain that increase in flow.

  9. I’m curious here if anyone knows of any studies done by Roger C. Bales which may have documented any increase in stream flows where millions of dead trees were located anywhere and if it were really significant enough to justify his claims for the Irrigation Districts in the valleys below ? Just curious.

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