Finding: Forest fires in Sierra Nevada driven by past land use – not climate

From the University of Arizona and Penn State comes this inconvenient finding.

The low-to-moderate intensity surface fire in this prescribed burn will lower the fuel load in this forest in the Lake Tahoe Basin. CREDIT Alan H. Taylor

The low-to-moderate intensity surface fire in this prescribed burn will lower the fuel load in this forest in the Lake Tahoe Basin. CREDIT Alan H. Taylor

Forest fire activity in California’s Sierra Nevada since 1600 has been influenced more by how humans used the land than by climate, according to new research led by University of Arizona and Penn State scientists.

For the years 1600 to 2015, the team found four periods, each lasting at least 55 years, where the frequency and extent of forest fires clearly differed from the time period before or after.

However, the shifts from one fire regime to another did not correspond to changes in temperature or moisture or other climate patterns until temperatures started rising in the 1980s.

“We were expecting to find climatic drivers,” said lead co-author Valerie Trouet, a UA associate professor of dendrochronology. “We didn’t find them.”

Instead, the team found the fire regimes corresponded to different types of human occupation and use of the land: the pre-settlement period to the Spanish colonial period; the colonial period to the California Gold Rush; the Gold Rush to the Smokey Bear/ fire suppression period; and the Smokey Bear/fire suppression era to present.

“The fire regime shifts we see are linked to the land-use changes that took place at the same time,” Trouet said.

“We knew about the Smokey Bear effect — there had been a dramatic shift in the fire regime all over the Western U.S. with fire suppression. We didn’t know about these other earlier regimes,” she said. “It turns out humans — through land-use change — have been influencing and modulating fire for much longer than we anticipated.”

Finding that fire activity and human land use are closely linked means people can affect the severity and frequency of future forest fires through managing the fuel buildup and other land management practices — even in the face of rising temperatures from climate change, she said.

The team’s paper, “Socio-Ecological Transitions Trigger Fire Regime Shifts and Modulate Fire-Climate Interactions in the Sierra Nevada, USA 1600-2015 CE,” is scheduled for publication in the online Early Edition of the Proceedings of the National Academy of Sciences the week of Nov. 14.

Trouet’s co-authors are Alan H. Taylor of Penn State, Carl N. Skinner of the U.S. Forest Service in Redding, California, and Scott L. Stephens of the University of California, Berkeley.

Initially, the researchers set out to find which climate cycles, such as the El Niño/La Niña cycle or the longer Pacific Decadal Oscillation, governed the fire regime in California’s Sierra Nevada.

The team combined the fire history recorded in tree rings from 29 sites all along the Sierra Nevada with a 20th-century record of annual area burned. The history spanned the years 1600 to 2015. However, when large shifts in the fire history were compared to past environmental records of temperature and moisture, the patterns didn’t match.

Other researchers had already shown that in the Sierra, there was a relationship between forest fire activity and the amount of fuel buildup. Team members wondered whether human activity over the 415-year period had changed the amount of fuel available for fires.

By using a technique called regime shift analysis, the team found four distinct time periods that differed in forest fire activity. The first was 1600 to 1775. After 1775, fire activity doubled. Fire activity dropped to pre-1775 levels starting in 1866. Starting in 1905, fire activity was less frequent than any previous time period. In 1987, fire activity started increasing again.

However, the frequency of forest fires did not closely track climatic conditions, particularly after 1860.

The researchers reviewed historical documents and other evidence and found the shifting patterns of fire activity most closely followed big changes in human activity in the region.

Before the Spanish colonization of California, Native Americans regularly set small forest fires. The result was a mosaic of burned and unburned patches, which reduced the amount of fuel available to fires and limited the spread of any particular fire.

However, once the Spanish arrived in 1769, Native American populations rapidly declined because of disease and other causes. In addition, the Spanish government banned the use of fire. Without regular fires, fuels built up, leading to more and larger fires.

The influx of people to California during the Gold Rush that began in 1848 reduced fire activity. The large numbers of livestock brought by the immigrants grazed on the grasses and other plants that would otherwise have been fuel for forest fires.

In 1904, the U.S. government established a fire suppression policy on federal lands. After that, fire activity dropped to its lowest level since 1600.

Starting in the 1980s, as the climate warms, fire frequency and severity has increased again.

Fires now can be “bad” fires because of a century or more of fire suppression, according to lead co-author Taylor, a professor of geography at Penn State.

“It is important for people to understand that fires in the past were not necessarily the same as they are today,” Taylor said. “They were mostly surface fires. Today we see more canopy-killing fires.”

Even in the face of global warming, people can affect the level of forest fire activity by managing the fuel available and other aspects of human land use, Trouet said.

“There has to be a consideration of both people and climate to predict and plan for future fire activity,” Taylor said.

###

The U.S. Forest Service, the George H. Deike, Jr. Research Endowment Fund, the U.S. Geological Survey and the Swiss National Science Foundation funded the research.

The paper: http://www.pnas.org/content/early/2016/11/08/1609775113

Socioecological transitions trigger fire regime shifts and modulate fire–climate interactions in the Sierra Nevada, USA, 1600–2015 CE

Abstract:

Twenty-first–century climate change is projected to increase fire activity in California, but predictions are uncertain because humans can amplify or buffer fire–climate relationships. We combined a tree-ring–based fire history with 20th-century area burned data to show that large fire regime shifts during the past 415 y corresponded with socioecological change, and not climate variability. Climate amplified large-scale fire activity after Native American depopulation reduced the buffering effect of Native American burns on fire spread. Later Euro-American settlement and fire suppression buffered fire activity from long-term temperature increases. Our findings highlight a need to enhance our understanding of human–fire interactions to improve the skill of future projections of fire driven by climate change.

 

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58 thoughts on “Finding: Forest fires in Sierra Nevada driven by past land use – not climate

  1. Michael Mann is at Penn State — I wonder what he thinks of this.

    FWIW — in case you missed it, this is another study which demonstrates how land use is more important than carbon emissions. This is why looking at trends and making conclusions is always wrong — (such as “we have three thousand weather monitoring stations now whereas one hundred years ago, we only had twenty. Therefore, greenhouse gases cause a proliferation of weather monitoring stations.” or “the number and length of hurricanes is directly correlated to the increase in satellites. Therefore, hurricanes are caused by satellites.”)

    • “Starting in the 1980s, as the climate warms, fire frequency and severity has increased again.”

      BUT

      “We were expecting to find climatic drivers,” said lead co-author Valerie Trouet, a UA associate professor of dendrochronology. “We didn’t find them.”

      I see Mikey Mann’s fingerprints all over this paper. The authors wanted to point out that land use is more important in fires than temperature and Trouet from UA says this. But I suspect that Taylor from Penn State was pressured into inserting Mann’s 2-cents worth!

      • I keep finding reports from Penn State that contradicts Mikey’s theories — $0.02 is about all it is worth. It seems like departments outside of his direct influence don’t feel the need to support his presuppositions. That’s one good mark for academic integrity.

      • Well we could say, that starting in the 1980s, arson became the crime of choice.

        I see she’s an Associate Professor of Dendrochronology. Perhaps it is her job to count the rings on the Yamal Charlie Brown Christmas tree each year, to make sure there is one more.

        I’m all for Dendrochronology. It’s the Dendro-(fillintheblank) studies that get my spameter going.

        G

      • I thought there was a change in the way the fire department tackled fires, having realised that try to prevent all fires just led to an abnormal buildup of combustible material. The more recent strategy being “let it burn”.

        Starting in the 1980s, as the climate warms, fire frequency and severity has increased again.

        So they still try to link this climate by saying “as the climate warms”. Without actually stating they find a causal link, they provide a sound bite for the media which will give this false impression.

      • Of course, “as the climate warms” like “in a warming world” is a standard code for AGW but with ‘plausible deniability’ built in to it just in case they get called to account in the future.

      • Greg,

        Also in the 1980s the Sierra Club really started raising a stink about prescribed burns, clear cut breaks and other fire control or fuel control operations. They say they are a conservation group, but they sure as heck aren’t doing anything good for the Sierras.

    • {sarc} Valerie Trouet is an Associate Professor at the Laboratory of Tree-Ring Research at the University of Arizona. (Personally, I was excited to discover there was a “Laboratory of Tree-Ring Research”. Some people find their niche and slip right into it. I didn’t even know there was an full-time position in Tree-Ring research let alone an entire laboratory dedicated to it.)

      Alan H. Taylor is the Director of Vegetation Dynamics Lab at Penn State (and he looks the part.) That almost sounds as exciting as watching grass grow, but I think I underestimated the field. His bio says, ” I address both theoretical and applied questions in my research and use a wide range of methodological approaches including tree ring analysis, spatial analysis and statistical modeling, simulation modeling, and historical ecology.”

      I feel confident that this year’s big video game release will be “Virtual Vegetation Dynamics in 3D”. {/sarc}

      • Perhaps the tree ring research department will uncover the mystery of why the end of Mikey’s treemometer graph went down instead of up requiring the trick of deleting it and adding instrument readings.

      • Gerry, England November 15, 2016 at 3:07 pm
        Perhaps the tree ring research department will uncover the mystery of why the end of Mikey’s treemometer graph went down instead of up requiring the trick of deleting it and adding instrument readings.

        That was Briffa’s data not Mann’s.

    • This is not new at all. In fact there are entire books and collections of essays on the ways that suppressing burning has affected fire intensity and frequency. Many, many moons ago now I worked for the USFS in the Sierra and occasionally spent weekends on call during intense fires. Fire managers gave talks about the way in which suppressing fires and the practices of intense cutting and slash scatter had been increasing fuel loads for decades. The Sierra Nevada biological communities are mostly “fire ecologies.” There plant species seeds including the Big Trees that can’t even germinate unless a fire comes by. It was a well known fact – dendrochronologically – that Yosemite was burned over complete;y during about a 25 -year span. This doesn’t mean the entire park burned all at once, but that in patches the entire park area would burn. Following the establishment of the park and the strict fire suppression protocols the park never saw a fire in 50 years until really big one less than 20 years ago. The fire managers I knew called the process of the development of multistory forest structures “fire ladders.” Fires burning slash on the ground would climb into understory shrubs, then into middle story, shade tolerant trees, and from them into the crowns, creating the monster fires we are familiar with now.

      Another just-so story told to California school children is the tall tale of how hardy European weeds, brought in as seeds stuck in the coats of cattle and sheep, crowded out the less hardy perennial grasses in the Great Valley. Again, fire suppression is the real culprit, since annuals are less resistant to fire, where the perennials have deep root systems that survive fires just fine.

      • In South Africa, one group of species (the fynbos) is highly reliant on grass fires for reproduction. Attempts at preventing such fires have been met by a lot of local opposition. And in the Kruger Park, controlled burns are used to provide future food for the herbivores, and to encourage movement of herds from one place to another following the food.
        Fire is GOOD for the environment!

  2. Now with marijuana plots popping up all throughout hidden sites in the Sierra Nevada foothills and valleys, expect there to be a large incentive to suppress fires by the natives.

    • I suspect that the “farmers” in these hidden plots will have removed most of the undergrowth in these areas. While the crop would, during the growing season, could provide the fuel it displaced that vegetation is removed during harvest. However these plots require sunshine and as such are not located under a dense canopy.
      More devastating to the local environment are the poor farming methods which exacerbate soil erosion and displace native flora and fauna.

      • The worst effects are from really nasty use of insecticides. In some regions it is advisable to get your trout tested before consuming too many.

  3. Our findings highlight a need to enhance our understanding of human–fire interactions to improve the skill of future projections of fire driven by climate change.

    The theory says that a warmer climate should have more forest fires because that is required for CAGW orthodoxy. On the other hand, the data says that the climate has little effect of forest fires.

    This reminds me of German propaganda during WW2. The Nazis wouldn’t admit that they were being beaten but some Germans figured it out anyway.

    I knew we were losing because our great victories kept getting closer to Berlin.

    A researcher can’t directly contradict CAGW orthodoxy but it’s easy to read between the lines.

  4. “We were expecting to find climatic drivers … we didn’t find them”

    Please appoint this woman to a high position within the EPA, or Interior, or White House Science Advisor

  5. Don’t know. I mean the people that tend those patches are not Always bright, responsible people that take all precautions to not start a forest fire. so more people in remote places doing stupid things will add up to a patchwork of burn sites. Gee…. mayby they do have green side to them

  6. Slightly off topic, but the rash of fires now occurring in the southeast US are suspected of being arson. One man has already been arrested in TN.

  7. It makes SO much more sense that humans can effect the local ecology than humans can affect the global climate. The former can be demonstrated as real with tangible evidence and repeatible experiments.

  8. “Forest fire activity in California’s Sierra Nevada since 1600 has been influenced more by how humans used the land than by climate, according to new research led by University of Arizona and Penn State scientists.”

    Any moron with a clue could figure this out.

    “We were expecting to find climatic drivers,” said lead co-author Valerie Trouet, a UA associate professor of dendrochronology. “We didn’t find them.”

    Hmmm, Dr, Trouet is not the kind of moron I was referring to. She is obviously interested in looking at the trees while missing the forest. I forgive people with blinders on.

    For the dimwits out there that couldn’t figure this out… To have a fire you need to have a few things

    Fuel is essential, the more the better. It helps to have dry conditions, the dryer the better of course, but dry conditions can happen at any time of the year. It helps to have hot conditions too because it helps to increase the drying, but like dry conditions having hot temperatures happens often enough during a year.

    So clearly the most critical part of the equation is the amount of fuel available and any changes in long term climate trends will be dwarfed by short and long term natural weather cycles.

  9. 1987 is when the temperature started rising in the Sierra Nevadas? I find that hard to believe. Especially since CO2 has been rising more or less steadily since the 1950’s.
    What else happened around 1987?
    One thing was the end of the Smokey Bear era where all fires were fought.

  10. “Twenty-first–century climate change is projected to increase fire activity in California”? How? The report/finding is behind a pay wall, so I was unable to see if they identified any studies that show any to-date increased fire activity in the Sierra Nevada specifically caused by a change in – average weather patterns. And “what” change could possibly increase fire activity in the SN? Yes, the SN is coming out of a drought and the fires have been more “extensive” because of the dry conditions over the past few years, something that also happened in the mid 80s – and many times before. But based on my experience and research I have not found any increase of fire incidences in the SN over the past 40 years, during which i lived in CA, owned a cabin in the SN and have visited almost every year since moving from CA, nor any increase in comparison to the historical record going further back, including Me-Wuk indian records.

    • …. nor any increase in comparison to the historical record going further back,

      But, but, but, …..milwaukeebob, ……. what about this …. “tree ring fire history record”? To wit:

      Excerpted from article:

      The team combined the fire history recorded in tree rings from 29 sites all along the Sierra Nevada with a 20th-century record of annual area burned. The history spanned the years 1600 to 2015.

      Were those tree-rings from the trees that were burned up in the forest fires, …… or the tree-rings from the new-growth trees that grew from seeds after the forest fires burned ……… or the tree-rings from the Lodgepole Pine Trees which truly Love Forest Fires?

      Or maybe it was tree rings from numerous 415 year old trees?

      • Exactly. Plus, what initiated each of those fires, particularly the ones say prior to any fire service records. The point being there is NO proof of any change in weather caused ignition. That being lightning.

  11. Climate change is magic…it’s always going to mess up something in the future

    We didn’t find any link to climate change….but we must prepare for what it will do in the future

  12. Human beings have been tending nature for upwards of 15,000 years in CA.

    By “tending” I mean impacting, managing, altering, stewarding, steering, trammelling, maintaining, conserving, sustaining, gardening, taking care of, utilizing, cultivating, renewing, etc. Human beings have fully occupied and been the keystone predators and vegetation managers in CA for millennia.

    All fire “regimes” in CA have been anthropogenic since before the Holocene even began. Through the use of fire, human beings created a vast (coast-to-coast) anthropogenic mosaic of prairies, fruit and nut orchards, craft fiber copses, berry fields, savannas, open and park-like forests, etc. as well as homes, communities, roads, canals, mounds, and other human-built features. Natural (lightning) fires did not dominate but instead merged into the already frequently human-burned mosaic.

    If not for human influences there would be no old growth trees in CA today. Tree species in CA do not require longevity of hundreds of years to reproduce. Trees typically seed into thickets. Thickets burn with 100% mortality at relatively young tree ages. Without human influences of (fire) thinning and understory (fire) management, individual trees do not survive for centuries.

    Nor do humans survive landscape-sized catastrophic fires which destroy food sources for years or even decades. Yet humanity did survive, sustain, and even thrive for thousands of years in CA (btw emitting scads of CO2 the entire time).

    Ecology is a historical science. Ecological theories which ignore historical human influences are wrong.

    • If not for human influences there would be no old growth trees in CA today… Please explain. There are bristlecone pines more than 4,000 years old. Quite a few redwoods over 3,000 years old.

      • Those are different eco systems George. Some eco systems may not have been influenced in the past but it should be considered.

        The basic problem with managing the environment is understanding all factors including man and naturally occurring change.

      • As far as old growth trees and human influence, there have been Native Americans in the area since the end of the last ice age, so the existence of human influnce is obvious. The Indians reportedly actively managed forests to encourage deer hunting conditions, which meant keeping the underbrush down with fire. As much of the losses to the Indians was due to smallpox and other Afro-Eurasian diseases, much of the changes in management practices done were before any anglos wrote any history, and instittuted a different forest management regime.

      • Dear Curious,

        Humans not only broadcast burned, they selectively burned individual trees. In particular, trees were burned to create firewood. But some trees were more valuable for other purposes such as providing fruit and nuts to feed humans and game.

        Historical anthropogenic landscapes contained scattered protected trees of high (alternative) value while most seedlings and saplings were flash burned to make hearth fuel. That is, trees with high alternative value were selected by humans to be NOT burned. Ditto some individual shrubs. Some herbaceous species, particularly root crops, were selected to BE burned for weeding purposes.

        Hence old growth trees of today are historical cultural artifacts. Indeed, it may be said that the vegetation mosaic in place in the Americas when Columbus landed was also a vast cultural artifact.

        Wilderness (nature isolated from human influence) is a pernicious ahistorical and ascientific myth. Just like CAGW.

      • The oldest tree in Europe is about 1,100 years old. Were Native Americans much better foresters?
        BTW, Native Americans did hunt in bristlecone forests, but they never settled there permanently – too cold, no water. You are referring to their management of Yosemite Valley floor, where they were far superior to the National Park Service.

  13. Nothing new here!

    About 20 years ago, a local Washington State US EPA employee approached my manager and myself after we had given a presentation on renewable energy from dairy farm manure. Some environmental problems are really too much energy in the wrong place issues. Using established engineering principles, could the problems be solved? Yes!

    The EPA guy asked if we could apply the same problems solving methods to forest health issues. It is not just California, it is the entire North America semi-arid forests. Yes!

    The information in this study has been known for at least 20 years.

    Here is my gripe with California and the climate crowd. They suck the money out the economy for things like wind turbines and solar panels that are very ineffective at mitigating climate change while adding a new set of environmental impacts.

    There is nothing glamours about dairy farm manure or too much fuel in the forest. Addressing these have immediate positive environmental impacts on each of the local communities. These projects would also be effective at reducing ghg emissions. This is called a win-win.

    The problem with the climate crowd is they are one issue idiots wearing blinders.

  14. The article states, “Fire activity dropped to pre-1775 levels starting in 1866. Starting in 1905, fire activity was less frequent than any previous time period.”

    Although not mentioned in the article, there was intensive lumbering after 1848, Homes had to be built for the miners and heated in the Winter. Wagons had to be built to haul supplies. Timbering was needed for the mine tunnels, headframes and stamp mills. Wood fuel was needed to retort the amalgam and melt the gold. Huge quantities of wood were consumed to build miles of sluice boxes along all the major rivers of the Sierra Nevada during the period of hydraulic mining, which effectively ended about 1884. Eventually, lumber was exported to San Francisco to re-build scuttled ships and build merchants shops; there was a resurgence in demand for lumber after the 1906 San Francisco earthquake. The Sierra Nevada of 1866 looked quite different from what it did in 1847 or what it looks like today. There was even extensive lumbering of redwoods in the Santa Cruz Mountains during the Gold Rush era. It is thought by some that the relatively pure stands of redwoods in the Coast Ranges was the result of annual aboriginal burning of the forests to open them up and improve browsing conditions for deer and elk, a primary food source. Humans have been modifying the landscape since they came down out of the trees.

  15. Another potential factor, Grazing or lack thereof. Grazing culls under-story and keeps the grasses in line.

  16. “We were expecting to find climatic drivers,” said lead co-author Valerie Trouet, a UA associate professor of dendrochronology. “We didn’t find them.”
    Clearly, not enough money was paid for this research. With enough money, you can always find the “climate” connection.

  17. As an Australian Forester these findings are very similar to Australian forest history. More definitive work is the recent book “Fire Stick Ecology” by Vic Jurksis.

    • I endorse Mr Massey’s comment
      California is the state of the US most similar
      climatically to much of southern Australia
      There the aborigines like the US Indians practised fire stick burnoffs to keep the undergrowth clear to encourage grass which attracted the kangaroos they hunted
      Early explorers commented on the open parkland like forests
      We have a 20 acre property in hilly heavily treed country in central Victoria
      A nearby long time resident told me his grandparents told him when they were young it was possible to ride a horse thru many of the local forests You could not do that now
      With demise of the aborigines and logging
      the overgrown forests have become fire hazards resulting in periodic huge out of control wild fires in Southern Australia
      An investigation into devastating fires with loss of over 170 lives found authorities had not
      carried out sufficient cool season burning off which replicates the controlled burns of the aborigines to remove forest floor fuel which
      enables the hot dry season wildfires
      As you would expect they get blamed on climate change overlooking the huge near state wide fires of 1939 and in the late 1890’s

  18. “Starting in the 1980s, as the climate warms, fire frequency and severity has increased again.”

    That was strictly coincidental. The increased fire frequency and severity were a result of Forest Service and BLM policies which decreased logging and REAL forest management. My friends and neighbors who were employed by those agencies predicted those outcomes when the policies were introduced in the 1970’s.

    The terrible fires did not occur so much on privately managed forest unless there were federal legal/judicial impediments to good forest management practices.

    Living in a county which is mostly owned by the Federal government, watching the eco-frauds at work in the Forest Circus and BLM, and seeing the great increase in undergrowth, I am very surprised that there aren’t even worse fires.

    • Exactly. As usual, a half-truth from the Green Blob.

      Yes, Federal fire suppression programs started in 1904. From then until the nuts took over, they managed the forests – people were allowed in to clear and haul away deadwood, grazing permits were issued to keep down the grasses, logging companies were allowed into selected regions to create fire breaks and keep canopy fires limited.

      The increase in the 1980s has NOTHING to do with the climate – except the political one, that put the ignorant children in charge of our forests.

      • In Colorado into the early 90s or just the 80s, we could harvest deadwood with a permit. They stopped that, saying it was too damaging to the forests. I guess they’d rather see them burn in place.

    • I’ll probably say something like “$!@#! broom” on my death bed. Absolutely hate the stuff. Well, at least it keeps me in shape.

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