Sheep study confirms a premise of McIntyre & McKittrick 05

Yesterday, I published a press release titled Tree ring widths more affected by sheep than temperature in which researchers in Norway published a peer reviewed study stating:

“We found tree ring widths were more affected by sheep than the ambient temperature at the site, although temperatures were still visible in the tree ring records. This shows that the density of herbivores affects the tree ring record, at least in places with slow-growing trees.”

They went on to say that “This study does not mean that using tree rings to infer past climate is flawed as we can still see the effect of temperatures on the rings…”, but according to MM05 below, that doesn’t seem to be fully accurate.

John Muir (founder of the Sierra Club) described them as “hooved locusts”.

Figure 8. Sheep grazing in ponderosa pine forests and grasslands near Flagstaff, AZ, ca. 1899. Image 21a by F.H. Maude, Cline Library Special Collections, Northern Arizona University. Retrieved from http://www.cpluhna.nau.edu/Change/grazing.htm

From MM05:

There is one other issue that needs to be canvassed and eliminated prior to reliance on bristlecone pines. The pulse in bristlecone pine growth is contemporaneous with a pulse in woody plant growth throughout the American Southwest, attributed to overgrazing by sheep in the late 19th Century (see Figure 8),

…which in turn followed the extension of the railroads [Allen, 1998; Allen et al., 1998]. Sheep differ from otherspecies in that they will completely destroy grasslands by eating down to the roots, leaving barrens [Allen, 1998]. Although Allen [1998] only documented the expansion of pinyon pines and junipers into terrain formerly occupied by 19th century grasslands, Allen (2004, pers. comm.) did not exclude the possibility of a similar effect involved in anomalous 20th century growth for bristlecone pines, but was unaware of any studies on the topic.

There is a published reference to the introduction of large commercial sheep flocks in the late 19th century in the White Mountains CA [St. Andre et al. 1967], where the key sites of Sheep Mountain and Campito Mountain are located. The founder of the Sierra Club, John Muir, complained of the depredations of sheep in the Sierra Nevadas (adjacent to the White Mountains) as “hoofed locusts” [Muir, 1911]. Carl Purpus, a late 19th century botanical collector in the Sierra Nevadas, stated in 1896 that commercial flocks had cleaned out all grass to the top of Old Mt Whitney [present-day Mount Langley, which reaches 4,280 m] [Ertter, 1988]. Allen (pers. comm., 2004) said that there was a large commercial sheep trail at Jicarita Peak NM, another bristlecone pine site studied by LaMarche and Stockton [1974]. In severe high-altitude terrain, even after the departure of commercial flocks, a small population of bighorn sheep could prevent the re-establishment of grass (Leslie Thomas, Colorado Springs, landscape architect, pers. comm.)

Since grass (and other herbs) compete with pines for scarce moisture, one can hardly exclude, on a priori basis, thepossibility of a connection between anomalous 20th century growth rates of bristlecone pines and a growth release following 19th century overgrazing, as experienced elsewhere in the American Southwest.

http://www.climateaudit.info/pdf/mcintyre.ee.2005.pdf

Like the many other factors in Leibigs law affecting plant growth, sheep are just one more variable not considered by Mann et al. The evidence keeps mounting that that hockey stick is made of woody assumptions that don’t hold up under scrutiny.

Ironically, The Sheep Albedo Feedback posited by Real Climate regular  Ray Pierrehumbert is starting to look plausible. [/sarc Actually it was a slam at MM05]

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40 thoughts on “Sheep study confirms a premise of McIntyre & McKittrick 05

  1. Turn the tree ring graph upside down…..and they can still tell the difference between sheep and temperature

    yeah right

  2. Overgrazed land responds differently to rainfall events – In normal lands with normal vegetation, the moisture hits the earth and is slowed by the plant material and slowly absorbed into the earth to feed the trees, shrubs, etc., – in overgrazed land, in contrast, there is little plant material to slow the water and it cascades down the watershed and much, much less rain is absorbed and the trees and the aquifers suffer…

  3. So the trees gain from reduced competition with grass, but lose due to reduced rain retention of bare soil, but gain from additional manure, but lose from nibbled leaves, but gain from reduced intra-species competition, but lose from … (you get the idea)

  4. This could be baaaaaa-d news for Mann (sorry, couldn’t resist that hanging curveball)

  5. For some reason, this reminded me of the Johnny Carson/Carnac The Magnificent Sis-Boom-Bah joke. Unfortunately, the audio and video are out of synch:

  6. The study states that:
    1) The influence of sheep is bigger than the influence of temperature.
    2) That once the eliminated the influence of the sheep, they could still see the temperature.

    These researchers knew with a high degree of certainty the number of sheep in the area of their tests trees, so they could calculate and remove the sheep factor.

    Now, pray tell, just how does someone who doesn’t know with the same degree of certainty, the number of sheep in the immediate vicinity of a particular tree in a particular year, figure out how big of a sheep factor to remove.

    The items mentioned would help to determine relative number of sheep in a geographical region and over a period of several years, but they aren’t specific enough to figure out how to adjust one tree, in any one year.

  7. But are the sheep in the southwest teleconnected to the trees in the Urals? Something to ruminent over I believe.

  8. I’d suggest that there is slight problem with a sheep-bristlecone connection. I’ve been to several bristlecone stands: White Mountains, Spring Mountains, Great Basin National Park (Wheeler Peak). I did not observe vegetation that could provide forage for sheep at any of these bristlecone stands. They were all rocky terrain (talus/scree) mostly devoid of any vegetation other than the bristlecones.

    Maybe the sheep ate it all back in the 1800s, but given the altitude and overall lack of soil development, I would doubt that.

  9. When I was about 13 in 1970 we went to the Redwood forest outside of San Fransisco. There I learned that tree rings grew at different rates due to temperature, rain, and many other factors, presumably including CO2. I don’t understand how the guild in the Redwood Forest in 1972 knew that there were many factors in tree ring growth, but in 1998 neither Mann, Bradley nor Hughes knew it.

  10. A number of creatures actually graze on conifers, at least occassionally. Deer, elk, porcupines are three that I have seen myself, with the damage especially visible after a winter of deep snow. I’m not saying anything here specifically about the Urals, but if all this bio-modification impacts tree-ring development, and Briffra’s work is actually about only a few or 1 tree, then we have to understand the history of those specific trees.

    The idea with small samples is that they are representative of the larger population, that they do not have individual lives that differ from the main. We think of trees as stone pillars in nature, unresponsive but to the largest of influences. Perhaps that is a simplistic view. Perhaps small samples are not insensitive to very local influences, unlike what Briffa-Mann-Jones-Important Personages at the IPCC might have thought.

    Ooops.

  11. Briffa pretty much proved tree rings were bad temperature proxies when they declined in size from 1960 onwards while thermometer readings were averaging a slight increase. Of course he chose to hide the decline by substituting in thermometer readings.

  12. Give me a break! Deer are browsers and will even strip trees of bark and kill them outright. Elk do some browsing but more grazing. Moose do both depending upon what is available. Do we have a count density on these populations over time and all of the other coincidental possible fauna that could impact tree growth? Again we have nonsensical studies. Too many unknown variables. Tree rings, what a hoot. This is a great site and I learn much by lurking here but I am coming to the conclusion that at least 90% of climate “science”, irrespective of the spin it takes, is sheep dip and AGW is absolute sheep do-do. We cannot even measure current temperatures accurately on a global basis due to the many factors that have been cited on the site.

  13. This changes nothing. If aliens landed and said AGW is less then noise in the data and can safely be ignored the politicians (and I include the so called scientists in this group) would still push ahead. I can’t come up with one scenario were they would back down or retreat. Can you?

  14. Land use (amount of nutrients and number of type of surrounding trees and surrounding environment affect tree growth (tree ring thickness) … Forest fires and lightening strikes affect tree ring thickness as well. Makes sense.

    So, if the land quality and the number of forest fires around all of the trees in every study cited have been uniform for 2000 years, or have been properly compensated for, then tree rings can be used as a proxy for temperature changes of less than 1/10 of one degree over 2000 years.

    But … rainfall changes from year to year and from decade to decade. And the number of animals around the trees seems to affect tree ring thickness as well.

    So, if rainfall amounts and the number of sheep (other animals) around the trees and the land quality and the number of forest fires around all of the trees in every study cited have been uniform for 2000 years, or have been properly compensated for, then tree rings can be used as a proxy for temperature changes of less than 1/10 of one degree over 2000 years.

    But CO2 levels affect tree growth.

    So, if CO2 levels and rainfall amounts and the number of sheep (other animals) around the trees and the land quality and the number of forest fires around all of the trees in every study cited have been uniform for 2000 years, or have been properly compensated for, then tree rings can be used as for temperature changes of less than 1/10 of one degree over 2000 years……

  15. Alex says:
    July 27, 2011 at 9:45 am
    “This changes nothing. If aliens landed and said AGW is less then noise in the data and can safely be ignored the politicians (and I include the so called scientists in this group) would still push ahead. I can’t come up with one scenario were they would back down or retreat. Can you?”

    Don’t know about the politicians but the “scientists” would stop the BS if there was no money in it.

  16. Every variable brought to the (mutliplication) table brings with it a level of uncertainty (or ‘variance’ in statistics-speak). This one (the space-time distribution of grazing sheep) appears to have a rather large uncertainty; large enough that quantitatively deconvoluting the effects of this and other variables affecting tree-ring thicknesses becomes statistically indefensible.

  17. I don’t know about other bristlecone sites, but I doubt anyone ever attempted to graze sheep in the upper parts of the White Mountains. There’s little/no water and very little forage there. I spent some days some years ago wandering around lower down near the Winter closure gate. I don’t think I saw any vertebrates of any size other than a few birds. No sheep, no deer, no rabbits, no squirrels, no snakes. And no scat from large vertebrates.

    BTW, the Summers there are quite warm. Plenty warm enough for plant growth. I’d guess that the tree rings there tell one more about precipitation than temperature.

  18. “John Muir (founder of the Sierra Club) described them as “hooved locusts”.”

    Ahem. I think he got his sheep and goats mixed up …

    As for sheep overgrazing, eating all the grass down to the bare soil – hm, strange. This does not happen in Wales or the Pennines, which carry lots of sheep but have a year-round grass cover.
    I’m sure our Kiwi friends would agree.
    Sheep don’t just wander aimlessly around.
    For example in the Yorkshire Dales, there were established flocks of semi-feral sheep (Helmsdale) where the leading ewes knew their territories so well, and led their flocks from one place to the next that there never was overgrazing. Such ‘maps’ were passed on from generation to generation. That was why the Foot-and-mouth outbreak at the beginning of the Millenium in Great Britain was such a disaster. Whole flocks were culled – and the next generation had lost the knowledge.

    There is another great way to prevent overgrazing: moving flocks from one place to the next. Mind – you’d need some well-trained Border Collies for that job … ask any Welsh, English, Irish or Scottish sheep farmer …

  19. Are you sure it’s only sheep that ‘will completely destroy grasslands by eating down to the roots, leaving barrens [Allen, 1998].’? In Africa goats are blamed for the same thing because of over grazing. 30 years ago in South Africa I saw dramatic evidence of this with stable grassland one side of the fence and bare red earth and erosion the other side at a ‘Homeland’ border. Goats and overgrazing was the explanation given by my sheep farmer host. I was told that goats pull the whole plant up rather than just nibbling down to the roots. There are bound to be experts (not me obviously) on this out there in WUWT land.

  20. Maybe four-legged sheep influence ring width but it is mainly two-legged sheep who put the mess in the densities of tree rings.

    See this graph (unfortunately in french)

    Switzerland normalized detrended values from 1915 to 1998

    The vertical scale is the standard deviation calculated before removing trends.
    Standard deviation is 0.71 ° C and the gap trends MXD-T is 1.7 ° C per century.

    – MXD closely correlate temperature except a large linear factor.
    – It is likely that blocking effect appears for high temperatures (see the period 1945-1950).
    – Curiously, We do not see any particular phenomenon around 1960.
    – Some land grass free between T and TRW.

  21. Dave Stephens says:
    July 27, 2011 at 8:13 am
    “Overgrazed land responds differently to rainfall events… ”

    I recall a UK programme by Chris Packman saying exactly this about the Welsh uplands. Sheep grazing has removed the upland bogs that used to retain large quantities of water. The quandary is the sheep can be eaten but the Welsh uplands now hold less water for Manchester and surrounding conurbations. Chris felt that the sheep should be removed and the hills returned to upland bog which would increase their water capacity thereby providing a more reliable water supply for the Manchester conurbations year round. This of course would also cool the local atmosphere more effectively than any carbon offsets, although I wouldn’t say that Manchester is renowned for either a hot or dry climate!

  22. Given the way the AGW crisis industry has been trying to scare the public so they can herd them like sheep, this story has all sorts of analogy potential.

  23. The Passenger pigeon used to roost in trees, including the bristlecone pine. What if the dropping of the Passenger pigeon, there were 3 billion to 5 billion of them, were the main source of nutrients?
    Moreover, the European Earthworm completely changes the root ecology of trees, first dropping then increasing their growth rate. When, within the last 500 years since their introduction, did they enter the bristlecone pine environment?

  24. Plausible explanation – I am aware of a similar effect sheep had from their introduction in rural Western Australia – there the introduction resulted in a unique, once off, mass erosion event that caused a movement of residual soil downslope by some hundreds of meters. The soils are now stablised and most of the sheep removed, but few people, especially in the sciences who tend to be more blinkered than lay people, accept it.

  25. I can’t believe there are still people who defend the hockey stick graph. With that graph, you have to assume that climate doesn’t change (and hasn’t done so for 2000 years) and that current trends are unprecedented (this is why it’s alarming). That precludes the use of the term “climate change”. It’s like the AGW people have a self-contradictory theory on their hands.

    If climate change is real, then the hockey stick graph is wrong. And if current warming is unprecedented, then climate change is not real. Something’s gotta give, no?

  26. A typo methinks.
    “is made of woody assumptions that don’t hold up under scrutiny.”

    s/woody/woolly/

  27. I thought that another study of the Bristlecones did NOT confirm the high rates of growth??? This is just PILING IT ON!! 8>)

  28. @Tom T – July 27, 2011 at 9:12 am:

    When I was about 13 in 1970 we went to the Redwood forest outside of San Fransisco. There I learned that tree rings grew at different rates due to temperature, rain, and many other factors, presumably including CO2. I don’t understand how the guild in the Redwood Forest in 1972 knew that there were many factors in tree ring growth, but in 1998 neither Mann, Bradley nor Hughes knew it.

    Not only is this patently obvious – that rain and other factors affect the tree rings – but I’ve commented before (here and/or at CA) about a study of cypresses in S Carolina that talks ONLY of precipitation as a forcing in tree rings.

    If there are multiple forcings, someone needs to delineate what portion each forcing is accountable for. And I am certain that this varies based on the site and the micro-location (drainage, humus content, available sunlight, etc. added to precip and temp), and if so, there cannot be a simple global average that can be applied. This is a complex and compound situation, as compound as there are numbers of trees in the world.

    I also cannot credit that the climatologists named did not know in 1998 that there were many factors in tree ring widths and densities.

  29. It gets complicated, my understanding of the soil impact of grazing from ‘best’ to ‘worst,’ is cattle -sheep – goats. Sheep eat to the stubble, leaving the root and soil structure intact to regenerate after rain, they can reduce the understory and release more moisture to the trees and also add soil fertilizer. As hard hooved animals they can compact the soil and reduce surface water penetration and increase run-off on slopes. Ewes short of minerals can even strip bark off trees.
    I don’t know about the ‘hooved locusts’ comment by Muir, it would depend upon the grazing intensity.

  30. It will be interesting to see if catastrophic holocaust affects tree growth in the White Mountains, recently subjected to the Wallow Fire — at 538,000 acres the largest in Arizona state history.

  31. The comments relating to sheep grazing are true for the arid grass lands of the US west. This is cattle country. Sheep prefer cooler damper conditions where the grass growth keeps up with the grazing resulting in zero grass death. The grass lands of Wales and Scotland seem to accomodate millions of sheep with no problem. Have done for decades.

    Don’t blame the sheep blame the farmer.

  32. Bob Tisdale says:
    July 27, 2011 at 9:01 am

    For some reason, this reminded me of the Johnny Carson/Carnac The Magnificent Sis-Boom-Bah joke.

    Quibbler that I am, I always thought it should have been changed to, “Sis-Bah-Boom”. >:(

    The ruination of grasslands is one major reason sheep need shepherds: to move them along before they wreck the resource they depend on. Would that Greens had emotional and intellectual shepherds …

  33. Brian H says, July 28, 2011 at 4:44 am:

    “Would that Greens had emotional and intellectual shepherds …”

    I propose the deployment of well-trained Border Collies. They have shown that they can deal with sheep, even recalcitrant ones. They would have no problem shepherding Greens to pastures new, such as some nice Tundra – and keeping them there.

    Sorry – I couldn’t resist …
    ;-)

  34. Does this explain the divergent problem with the tree ring data since the mid 20th century?

  35. SteveE,
    Probably not, for several reasons:
    – Sheeps are supposed to affect the width of rings but probably not the densities which present however a similar divergence.
    – Every trees are not affected by sheeps but the vast majority of dendro diverge.
    – Other proxies such as glaciers have a similar divergence and I doubt that the trampling of sheep can explain this particular case.
    Another thing, divergence is represented by a factor more or less constant that appears likely at the beginning rather than the mid-twentieth century.

  36. This study, if correct, says that sheep CAN affect tree ring growth.

    It doesn’t say that sheep were present at all sites used for analysis.

    Were they? Do we know?

    My conclusion is merely that the factors which affect tree ring growth may be broader than merely ‘annual temperature’ and carbon dioxide.

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