Giant Sequoias Yield Longest Fire History from Tree Rings

Mar 17, 2010 By Mari N. Jensen
This cross-section of a giant sequoia tree shows some of the tree-rings and fire scars. The numbers indicate the year that a particular ring was laid down by the tree. (Credit: Tom Swetnam)

(PhysOrg.com) -- California's western Sierra Nevada had more frequent fires between 800 and 1300 than at any time in the past 3,000 years, according to a new study led by Thomas W. Swetnam, director of UA's Laboratory of Tree-Ring Research.

A 3,000-year record from 52 of the world's oldest trees shows that California's western was droughty and often fiery from 800 to 1300, according to a new study led by University of Arizona researchers.

Scientists reconstructed the 3,000-year history of fire by dating fire scars on ancient giant sequoia trees, Sequoiadendron giganteum, in the Giant Forest of Sequoia National Park. Individual giant sequoias can live more than 3,000 years.

"It's the longest tree-ring fire history in the world, and it's from this amazing place with these amazing trees." said lead author Thomas W. Swetnam of the UA. "This is an epic collection of tree rings."

The new research extends Swetnam's previous tree-ring fire history for giant sequoias another 1,000 years into the past. In addition, he and his colleagues used tree-ring records from other species of trees to reconstruct the region's past climate.

The scientists found the years from 800 to 1300, known as the Medieval Warm Period, had the most frequent fires in the 3,000 years studied. Other research has found that the period from 800 to 1300 was warm and dry.

"What's not so well known about the Medieval Warm Period is how warm it was in the western U.S.," Swetnam said. "This is one line of evidence that it was very fiery on the western slopes of the Sierra Nevada - and there's a very strong relationship between drought and fire."

Droughts are typically both warm and dry, he added.

Knowing how giant sequoia trees responded to a 500-year warm spell in the past is important because scientists predict that climate change will probably subject the trees to such a warm, dry environment again, said Swetnam, a UA professor of dendrochronology and director of UA's Laboratory of Tree-Ring Research.

During the Medieval Warm Period extensive fires burned through parts of the Giant Forest at intervals of about 3 to 10 years, he said. Any individual tree was probably in a fire about every 10 to 15 years.

The team also compared charcoal deposits in boggy meadows within the groves to the tree-ring fire history. The chronology of charcoal deposits closely matches the tree-ring chronology of fire scars.

The health of the giant sequoia forests seems to require those frequent, low-intensity fires, Swetnam said. He added that as the climate warms, carefully reintroducing low-intensity fires at frequencies similar to those of the Medieval Warm Period may be crucial for the survival of those magnificent forests, such as those in Sequoia and Kings Canyon National Parks.

Since 1860, human activity has greatly reduced the extent of fires. He and his colleagues commend the National Park Service for its recent work reintroducing fire into the giant sequoia groves.

The team's report, "Multi-Millennial Fire History of the Giant Forest, Sequoia National Park, California, USA," was published in the electronic journal Fire Ecology in February. A complete list of authors and funding sources is at the bottom of this story.

To study tree rings, researchers generally take a pencil-sized core from a tree. The oldest rings are those closest to the center of the tree. However, ancient giant sequoias can have trunks that are 30 feet in diameter - far too big to be sampled using even the longest coring tools, which are only three feet long.

To gather samples from the Giant trees, the researchers were allowed to collect cross-sections of downed logs and standing dead trees, he said. It turned out to be a gargantuan undertaking that required many people and many field seasons.

"We were sampling with the largest chain saws we could find - a chain-saw bar of seven feet," he said. "We were hauling these slabs of wood two meters on a side as far as two kilometers to the road. We were using wheeled litters - the emergency rescue equipment for people - and put a couple hundred pounds on them."

To develop a separate chronology for past fires, co-authors R. Scott Anderson and Douglas J. Hallett looked for charcoal in sediment cores taken from meadows within the sequoia groves.

"We can compare the charcoal and tree-ring fire records. It confirms that the charcoal is a good indicator of past fires," Swetnam said.

Such charcoal-based fire histories can extend much further into the past than most tree-ring-based fire histories, he said. The charcoal history of fire in the giant sequoia groves extends back more than 8,000 years.

Increasingly, researchers all over the world are using charcoal to reconstruct fire histories, Swetnam said. Many scientists are analyzing the global record of charcoal to study relationships between climate, fire and the resulting addition of carbon dioxide to the atmosphere.

Explore further: UN climate talks shuffle to a close in Bonn

Related Stories

Large trees declining in Yosemite

Jul 29, 2009

Large trees have declined in Yosemite National Park during the 20th century, and warmer climate conditions may play a role.

Recommended for you

UN climate talks shuffle to a close in Bonn

8 hours ago

Concern was high at a perceived lack of urgency as UN climate negotiations shuffled towards a close in Bonn on Saturday with just 14 months left to finalise a new, global pact.

Study shows no lead pollution in oilsands region

Oct 24, 2014

New research from a world-renowned soil and water expert at the University of Alberta reveals that there's no atmospheric lead pollution in Alberta's oilsands region—a finding that contradicts current scientific ...

User comments : 22

Adjust slider to filter visible comments by rank

Display comments: newest first

Loodt
1 / 5 (8) Mar 17, 2010
So the MWP can be traced to California?

Wait until Mann gets hold of this data and see it gets tortured to confess to an Ice Age!
lengould100
2.3 / 5 (3) Mar 18, 2010
Accept Mann's data or publish your own, properly reviewed.
Loodt
1.6 / 5 (7) Mar 18, 2010
Anybody that sticks up for Mann is morally corrupt, intellectually challenged and the opinion can be disregarded with the contempt it deserves.

And, this article was paid for by BIG OIL!
JayK
3 / 5 (2) Mar 18, 2010
Loodt, do you have proof that anything Mann did was incorrect or do you just like to look like a fool?
Loodt
1 / 5 (4) Mar 18, 2010
JayK, does your HOD know you are working on that machine?

Mann is as innocent as Dr Joseph Mengele, both doing what they did in the belief they are fighting for a good cause!

JayK, towards the end of the last century I read 'the Bell Curve'. Two things stuck in my mind, the IQ difference between Orientals and WASPs, and that there is tremendous competition for brainpower from the big USA companies and Wall Street. The fact that you are working for neither of those means I've got your number.

I am sure that you are too useless to work for any private company, and hide in some obscure teaching post at a underfunded and second rate academic institution. You are so pathetic that you have to pay for own coffee!

No go back and impress the kids of the special school you teach at!
JayK
3 / 5 (2) Mar 18, 2010
So the answer is that you have nothing except for a big mouth. Why don't you come back when you actually have something useful to add?
Loodt
1 / 5 (4) Mar 18, 2010
So you pay for your own coffee!

Pathetic looser!

Come back when somebody pay you enough so that you don't have go to websites looking for people to impress with your useless outdated information!

I know your salary doesn't match your IQ, with US$1k per IQ point. Only a fool would work for less!
JayK
3 / 5 (2) Mar 18, 2010
I'm not sure how it is a function of my intelligence when you are unable to come forth with an argument against Mann's work. So far, you haven't approached the discussion with anything other than name calling and false accusations.

I've tried to address your concern, that Mann's work is somehow flawed, so I'll ask one more time: Can you please present the information that you use to make that statement so that it can be addressed in this or another forum?
Loodt
1 / 5 (3) Mar 18, 2010
To the treasurer of the coffee club, start here: -

http://joannenova...line-go/
JayK
3.7 / 5 (3) Mar 18, 2010
Yeah, nice blog.

Credibility? You don't need no stinkin' credibility.

1) No citations to the graphs. Fail!
2) Mixing Northern Hemispheric data with global data. Fail!
3) It has been clearly pointed out that atmospheric data (raobcore, in this case) has not tracked surface temperatures accurately and is still being understood. So fail by their implying anything of the sort.

Useless site. Thanks for wasting my time.
eachus
1 / 5 (2) Mar 18, 2010
First, let me state that I think that increased CO2 levels in the atmosphere have deleterious effects on human beings unrelated to temperature changes. Therefore when I advocate hanging Mann, et. al. out to dry, it is because they have falsified evidence and destroyed the public's trust in scientific objectivity.

Okay, on to the scientific method, which the climate mafia have tortured badly. It works like this: You create a hypothesis. "CO2 forcing causes global warming." You test this hypothesis against the real world, with experiments performed after you formed the hypothesis. These experiments can use data collected earlier, if you did not use it in creating the hypothesis. Shaky but sometimes, the only choice available. If the evidence falsifies the hypothesis, you throw it out and start over. This is what Mann, et. al., refuse to do.

The above article, and http://www.physor...477.html are enough to falsify the hypothesis, and the hockey stick graph.
JayK
3 / 5 (2) Mar 18, 2010
Fascinating, eachus. Please do tell how that falsifies the hypothesis, I'd be fascinated as well to read your peer reviewed entry as soon as it is ready!

As well, can you please provide the proof that Mann and the rest of them have falsified evidence? I'd love to see it, I've been looking everywhere and so far all I turn up are blogs making the claim with nothing to back it up.
Loodt
1 / 5 (4) Mar 18, 2010
Chairman of the coffee club.

I've been looking everywhere ...

And you wonder why you have to buy your own coffee?

Try harder, looser!
JayK
3 / 5 (2) Mar 18, 2010
How do I try harder and looser?

If you have all this wonderful proof, provide it. So far you've failed to provide anything with a bit of credibility. I'm willing to at least read what you provide, even when you won't do the same. Come on, give me some citations to a credible source. If you are so convinced that AGW is a scam, that they have falsified data, etc etc etc, then you must have come across a credible citation that will prove it to the rest of us "warmers", right?
eachus
2.3 / 5 (3) Mar 19, 2010
If you have all this wonderful proof, provide it. So far you've failed to provide anything with a bit of credibility.


Is global warming a part of your religion? If so, sorry, I didn't mean to question your religious beliefs. Otherwise, did you stop to think before posting that, or actually read the article we are discussing?

I am not a scientist, nor do I play one on TV. On the other hand, I am a statistician, and I have, as such, given advice to lots of scientists writing for peer reviewed journals on whether their application of statistics passes (scientific) muster.

When I first saw the infamous hockey stick graph, my first reaction was "where is the Little Ice Age?" followed quickly by, "What happened to Tambora (http://en.wikiped...Tambora) and Krakatoa? (http://en.wikiped...rakatoa)

Then I looked at the statistical methodology, and threw the hockey stick on my mental trash heap.
eachus
3 / 5 (2) Mar 19, 2010
I don't have to prove that the 1816 and 1883 volcanic eruptions occurred or that they had significant effects on the global climate. That was well studied by climatologists before Micheal Mann came along. I also don't have to "prove" that the MWP (medieval warm period) and Little Ice Age existed. (See above for research on the MWP in California.)

When Mann et. al. published data which ignored these well established climate events, it was up to the authors of those papers to object to and falsify the previous climate history of Earth. I'd flunk a Freshman who committed the statistical sins that Mann and company did in their "research." (The fundamental error was using assumptions of normality in what is clearly time series data.)

In other words, when asked to disprove the hockey stick, 1000 characters, or even 1 million characters are not enough. Does that mean that global temperatures are not at or near recent highs like the MWP? No.
JayK
1 / 5 (1) Mar 19, 2010
So have you published your rejection of both the 1997 MBH and the 2005 MBH papers as a review in a journal?

I'd love to read it. Somehow, though, I doubt you've done anything but whine about it.
Loodt
1 / 5 (3) Mar 19, 2010
JayK, Friday!

Remember to give the coffee machine a good wash!

Remember, you are not working on Wall Street and you are a Looser!

PinkElephant
5 / 5 (1) Mar 19, 2010
JayK, Friday!

Remember, you are not working on Wall Street and you are a Looser!
No, that just means he's not a criminal.

I take it, you are? Congratulations!
Loodt
1 / 5 (3) Mar 20, 2010
PinkElephant,

Late to the party and don't understand the drift of the conversation?

Don't flatter yourself; do you realy think that a Wall Street Banker would have time to faff around sites like these?

I am not an American and never claimed to be one.

Judging by the timing of JayK's posts he is either based in America or working afternoon shift in an Indian call centre. Given his lack of understanding of punctuation, I don't think he would make the grade for a callcentre - the competition is too great - so he must be an intellectual, at a second rate academic institution, specializing in Climate Change and Acupuncture!

po6ert
1 / 5 (1) Mar 20, 2010
a big "so what"to global warming. we live in an interglacial period in an ice age. we should be doing everything we can to pervent the return of an new glaciation and mitigate volcanic cooling episodes.

wait until glaciers start to cover the upper portion of the northern hemisphere as they did
12000 years ago! Increaseed co2 emmissions may have
prevented further distructive global cooling.

would someon like to prove that we are not preventing the onset of a new glaciation.

would anyone like to prove that global warming
would in fact be any more harmful than global
cooling?

by the way ad homindim attacks only indicate imaturity
HoboWhisperer
not rated yet Mar 21, 2010
They can't find a coring tool more than 3ft long?
Really? I would think that having one custom made would be cheaper than the process described in this article