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”.
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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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?
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.
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?
A typo methinks.
“is made of woody assumptions that don’t hold up under scrutiny.”
s/woody/woolly/
Katy bar the door! … and hide the decline! /sarc
I thought that another study of the Bristlecones did NOT confirm the high rates of growth??? This is just PILING IT ON!! 8>)
@Tom T – July 27, 2011 at 9:12 am:
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.
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.
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.
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.
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 …
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 …
😉
Does this explain the divergent problem with the tree ring data since the mid 20th century?
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.
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.