Salvage logging and re-seeding a forest after a wildfire helps reduce flooding and returns water levels to normal faster

A PR from Washington State University. The paper ($) is here.

Response to fire impacts water levels 40 years into future

Salvage logging and re-seeding a forest after a wildfire helps reduce flooding and returns water levels to normal faster, according to a new paper from a Washington State University researcher.

The paper, just published in the journal Hydrological Processes, shows that water levels are still increased up to 40 years after a fire.

“Trees work like straws, pulling water up out of the ground,” said Ryan Niemeyer, an adjunct faculty member in WSU’s Center for Sustaining Agriculture and Natural Resources (CSANR). “When you remove them, the water has to go somewhere. Flooding is common after a wildfire, as is elevated stream flow in subsequent summers. But seeing that the effect lasts for up to 40 years is a little surprising and certainly a new finding.”

Niemeyer wrote the paper with Kevin Bladon at Oregon State University and Richard Woodsmith of Woodsmith Watershed Consulting.

Natural fire starts a long-term experiment

Their research looked at the U.S. Forest Service’s Entiat Experimental Forest in north-central Washington, which burned in 1970. The fire likely started from a lightning strike, Niemeyer said.

Three distinct areas of the forest were observed, with two of them having salvage logging done to remove what remained of the burned trees. Those areas were also fertilized and native seeds were dropped on the area. The third area was left untouched.

The fire interrupted a planned logging experiment in the forest, so researchers at the time switched to monitoring the effects of wildfire, said Niemeyer, who grew up hunting and fishing in the Entiat watershed.

The original studies in the early ’70s showed that water levels in the watershed increased significantly after the fire. But the measurement equipment was removed after a few years, said the native Washingtonian.

Past decisions impact today

Fast forward to 2004, when a new grant allowed for stream flow monitoring equipment to be re-installed to measure the long-term impact the fire had on water levels. The measurement period was from 2004-11, after which Niemeyer, a hydrologist who is also a post-doctoral researcher at UC-Santa Barbara, and his colleagues spent five years analyzing the data.

After roughly 40 years, only one of the three areas still had water levels above the pre-fire baseline: the section that was left alone to recover.

“If you visit today, you can easily see that area has less mature vegetation compared to the re-seeded sections,” Niemeyer said. “The trees in the re-seeded sections are much bigger, and water levels are back to normal.”

Increased water levels can be positive and negative, he said. If you want more water coming down a stream for increased access to water for irrigation, for example, then you wouldn’t want to salvage any of the logs or re-seed the area.

But that extra water can have other impacts on the land, he said. Trees help hold soil in place when it rains, so erosion is higher in areas that aren’t re-seeded. That increases sediment going into the watershed, which can impact fish and other wildlife.

“It’s really a complex set of interactions, and each wildfire situation effects water and water usage differently,” Niemeyer said. “But now we know how long a fire impacts nearby water, and that those impacts can be reduced faster.”

Since it’s now been eight years since the sensors were removed, and 15 since they were first re-installed, the researchers are hoping to start another round of monitoring in the area. They plan to write a grant proposal to fund re-installing the sensors to see if, and when, the untouched area returns to normal water levels.


11 thoughts on “Salvage logging and re-seeding a forest after a wildfire helps reduce flooding and returns water levels to normal faster”

  1. “water levels are back to normal.”

    Says who? Why would you want to “reduce impacts sooner?” Is there a value judgment here about what’s positive and negative? Why wouldn’t “normal” post-fire conditions be the untreated area and water and sediment associated with that? (Maybe if the fire wasn’t “normal,” but this was a 1970 fire and nobody seems to be claiming that.)

    • Exactly, some studies talk about disturbance to increase water yield. This says replant to reduce peak flows, which might be natural given the natural disturbance. Another view might be that salvage and replanting is likely to unnaturally REDUCE streamflows in decades 2-7 after fire and replanting.

      • Of course, one could also say that cholera is “natural” but, that would never make it desirable.

        In places where re-burns are likely and potentially catastrophic, the reduction of dead and dying fuels is appropriate.

      • That’s why “natural” doesn’t make a very useful yardstick. For one thing, very few things are “natural” anymore (that is, hasn’t been influenced by humans).

        What these folks are saying is that “planting helped trees grow back and helped the soil recover so it didn’t wash away, (we can see those things) and water flows returned to where they used to be before the fire. Which seems like you could call it “recovery from disturbance” if you took the fire as a disturbance.

        Isn’t there some language about the “ability of ecosystems to recover from disturbance” somewhere in the planning reg?

        We don’t have to ascribe naturalness to any of this. If cutting trees is bad when people do it, because of loss of habitat, then getting more forest habitat must be good. If sedimentation is bad for streams when caused by roads, but good for streams when caused by fires.. well, it’s confusing.

        • In fact, sediment from roads is different from sediment from fires (sustained “press” disturbance vs natural short-term “pulse” disturbance). Getting more forest back quicker in a location may make sense if forests are lacking (below NRV) at a larger scale, but this was about local stream flow. Salvage logging does not mimic post-fire conditions, and reburns can be natural. I agree that safety concerns are going to outweigh ecological integrity in some places, which means that to achieve integrity at a larger ecosystem scale there should be compensation somewhere else.

          The definition of “ecological integrity” includes when an ecosystem “can withstand and recover from most perturbations imposed by natural environmental dynamics or human influence.” This implies can … recover “on its own.

  2. A related topic — press release from U. California, Davis:

    “Thinning Forests, Prescribed Fire Before Drought Reduced Tree Loss”

    “Thinning forests and conducting prescribed burns may help preserve trees in future droughts and bark beetle epidemics expected under climate change, suggests a study from the University of California, Davis.

    “The study, published in the journal Ecological Applications, found that thinning and prescribed fire treatments reduced the number of trees that died during the bark beetle epidemic and drought that killed more than 129 million trees across the Sierra Nevada between 2012-2016.

    “By thinning forests, we can reduce water stress and make forests more resilient to drought and climate change,” said the study’s lead author, Christina Restaino, a postdoctoral scholar at UC Davis in the Department of Environmental Science and Policy when the study was conducted.

    “The study also indicated that current rates of treatment are not sufficient to reduce the impacts of hotter droughts and large-scale bark beetle outbreaks. Expanding the use of managed fire under moderate fire-weather conditions, along with strategic thinning and prescribed burn treatments, may increase resilience across the forest, the researchers said.

    “There are currently too many straws in the cup,” said Restiano. “Denser forests use more water. We’re learning that fuel treatments used to reduce fire risk have multiple benefits. Forests that are more open and less dense are stronger in the face of insect outbreaks, too.”

    More at:

    • Similarly, bark beetles aren’t necessarily a bad thing (within their NRV) – unless your goal is a tree farm. I have read that forests that are unnaturally dense can contribute to low water flows that affect aquatic species.

        • I would say they are outside NRV to the extent we think their recent outbreaks are due to too many trees resulting from fire suppression. NRV is supposed to incorporate climate change (that’s why it’s not HRV). An ecological goal for thinning should be to keep beetles within their NRV, not to “preserve trees.” (But of course a landowner may have non-ecological reasons to preserve trees.)


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