From Wiley-Blackwell, via Eurekalert, something just plain surprising.
Nibbling by herbivores can have a greater impact on the width of tree rings than climate, new research has found. The study, published this week in the British Ecological Society’s journal Functional Ecology, could help increase the accuracy of the tree ring record as a way of estimating past climatic conditions.
Many factors in addition to climate are known to affect the tree ring record, including attack from parasites and herbivores, but determining how important these other factors have been in the past is difficult.
Working high in the mountains of southern Norway, midway between Oslo and Bergen, a team from Norway and Scotland fenced off a large area of mountainside and divided it into different sections into each of which a set density of domestic sheep was released every summer.
After nine summers, cross sections of 206 birch trees were taken and tree ring widths were measured. Comparing these with local temperature and the numbers of sheep at the location where the tree was growing allowed the team to disentangle the relationship between temperature and browsing by sheep and the width of tree rings.
According to lead author Dr James Speed of the NTNU Museum of Natural History and Archaeology: “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.”
The impact of large herbivores on tree rings has, until now, been largely unknown, so these findings could help increase the accuracy of the tree ring record as a way of estimating past climatic conditions, says Dr Speed: “Our study highlights that other factors interact with climate to affect tree rings, and that to increase the accuracy of the tree ring record to estimate past climatic conditions, you need to take into account the history of wild and domestic herbivores. The good news is that past densities of herbivores can be estimated from historic records, and from the fossilised remains of spores from fungi that live on dung.”
“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, and in lowland regions tree rings are less likely to have been affected by herbivores because they can grow out of reach faster,” he explains.
Tree rings give us a window into the past, and have been widely used as climate recorders since the early 1900s. The growth rings are visible in tree trunk cross sections, and are formed in seasonal environments as the wood is laid down faster in summer than winter. In years with better growing conditions (in cool locations this usually means warmer) tree rings are wider, and because trees can be very long-lived and wood is easily preserved, for example in bogs and lakes, this allows very long time-series to be established, and climatic conditions to be estimated from the ring widths.
The study was funded by the Norwegian Research Council and the Norwegian Directorate for Nature Management.
James D. M. Speed, Gunnar Austrheim, Alison J. Hester and Atle Mysterud (2011), ‘Browsing interacts with climate to determine tree ring increment’, doi: 10.1111/j.1365-2435.2011.01877.x, is published in Functional Ecology on 27 July 2011.
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When asked for comment about their effects on tree ring widths, possibly affecting paleoclimate studies based on tree rings, the sheep denied complicity and said repeatedly “Maaaa aaa aann Maaaa aaa aann“.
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For those wanting a primer on all the things that can affect tree growth, may I suggest this primer.
Bob L says:
July 26, 2011 at 8:38 pm
Judging by the decrease in the number of people who believe in AGW, I would have to say that sheep density is declining.
That’s certainly true in two areas familiar to me: Perthshire, Scotland and Haute Vienne France. In Haute Vienne the last couple of years has seen a huge change from sheep and cows to Maize and Sunflowers.
“The good news is that past densities of herbivores can be estimated from historic records, and from the fossilised remains of spores from fungi that live on dung.”
Oh for F@ur momisugly#$ sake.
Of course you can, dear.
This is, quite simply, too funny.
Hopefully and eventually some people will feel sheepish for thinking that temperature trends can be demonstrated with changes in tree ring growth. As shown here and in other posts and comments, there are just too many other and important influences on tree ring growth. But surely the three most important are water, (sun)light and suitable environment (some trees like alkaline soils, acid soils, nutrient rich, nutrient poor, lots of water, little water) which can change.
It looks like a tall order to identify temperature changes of such small magnitude over a 100 years using trees. Added to that, we do seem to be in a period of science where there is a kind of machismo in showing how incredibly fine one can measure: Global sea level rises of a few millimeters; Global temperature rises of 10ths of a degree over 10s of years,
Meanwhile global fish stocks are declining in numbers that are firmly to the left of the decimal point and there are over 23,500 nuclear warheads which exceeds the number of cities with a million people by over 23,000.
Ric Werme and JC make very interesting points. What is the real mechanism behind this effect on tree rings? If it is only the first few years then it is irrelevant, if it is over the liftime of the tree then what has it got to do with nibbling?
I hope you all realise that this is progress.
Climate scientists performed an actual experiment. It was designed, set up, maintained, measured and interpreted.
Well done.
Build up a temperature record from tree ring data. Use the temperature record to verify the tree ring data.
ugh?
Well in archaeological dating processes ie. carbon dating. Check out the Bristle cone pines saga.
I can’t remember exactly but tree ring growth is measured by the space between rings and how the trees growth can vary from year to year, especially in old trees and there’s been a drought. Carbon dating organic matter has a plus and minus factor of course, and is not as accurate for stuff that is tested that is younger than 2,000 years. I don’t think many trees survive
this long maybe their trunks do of course. But something happened years ago with the Bristle
cone pines, I can’t remember but I believe for some reason the atmosphere got bombarded with more carbon. Oh G don’t tell the alarmists?
One of the Bristlecone sites is located at “Sheep Mountain”…
I wonder why this mountain is having that name.
(h/t Steve Mc)
Not having read one comment, I polled the sheep and their masters and ……
Well hello Dolly.
I’m surprised that Steve when dropping in did notmpoint out that one of the more important tree ring chronologies in MBH98 comes from … [drum roll] … Sheep Mountain
Too Funny!
http://climateaudit.org/2008/01/31/more-mystery-at-sheep-mountain/
According to some research precipitation is far more important than temperature for tree ring separation. With so many probable errors in this system I still do not think tree rings are a good proxy for temperature.
You’ve “virtually” said it all, you naughty, naughty people! They still have that fundametal problem, how do they “know” their assumptions are correct just becaue the model produces what they expected it to produce. A circuitous argument if ever there was one! You still have to tell a computer programme to show what you want it to show all the way down the line, it doesn’t think for itself you know!
RockyRoad says:
July 26, 2011 at 8:44 pm
Ah, so Mann wasn’t counting tree rings in his sleep–he was counting sheep instead. I wish he’d wake up! Or should his “hockey stick” be renamed to “lamb chops”?
Curiously, or even disturbingly, a chop bone bears an uncanny resemblence to chunky Hockey Stick! However I am worried, when I got some graph paper out of the draw (some of us like to draw lines & curves still in this electronic age), I plotted 7/10°Celcius rise in global temperature over 150 years to 2000 using red ink against thin black-inked base lines, thing is I could hardly see it but that was because I changed the aspect ratio & scales accordingly. Suddenly it didn’t look all that dramatic after all! Playing games with “chartmanship” is such fun!
Quite a while ago, I lived in town (Chelmsford, Essex) I owned a ground-floor flat, with a small garden and was on a busy road, downhill of but slap next door to a petrol filling station.
One day, as the local market was closing, I bought the last 8 Leylandii plants that a stall holder had and I planted them, in a line about 4ft apart, at the foot of my lawn to make a bit a hedge between me and the traffic.
The didn’t take off spectacularly as Leylandii are want to do and 3 years later I moved jobs and rented the property out.
6 years later I sold the property and had to clear the furnishings- it was only then I noticed how these trees had grown. The one closest to the petrol station was maybe 7ft tall and each tree was about 6″ less than the previous one, decreasing in size in a perfectly linear fashion as they got further from the filling station. Why?
I assumed it was water/rain run-off from the forecourt of the filling station (Essex is very dry county) so that the first tree got loads of water and each one got successively less. as the water drained away downhill. But and if anything, forecourt run-off would be polluted and would stunt them if not kill them outright
But was it extra water?
Do trees thrive on petrol fumes, was it extra CO2, water vapour or heat from the cars as they queued to get in and out of the filling station. Was it something to do with people walking their dogs or drunks from the pub 100yards away. So, what was going on there?
DCC says:
July 26, 2011 at 8:51 pm
Did he say what the effect was? I didn’t see it. Does browsing stunt the ring growth or does sheep manure increase it? Or don’t they know?
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My thoughts exactly.
Another possibility that came to mind was that perhaps the sheep weeded out very small adjacent saplings, which if left undisturbed would eventually grow and compete for light and nutrients available for nearby more substantial trees.
I would not get too carried away with this paper which I see more as amusement than anything else. At most, it is a reminder that many factors which may not at first have been readily apparent can influence the accuracy of conclusions drawn from proxy evidence.
I question the validity of the implications of this research on tree ring data used in proxy records Since this data comes more from forest than scrub land). I hate proxies generally. At best they are a rough and ready indicator of trends, but can never be reliably tuned and since so many other ‘outside’ factors are at play on the development of the proxy, they cannot be used to quantify a specific sub set of one of the ‘outside’ factors at play. In my opinion, people try to read far too much into proxies, and all proxy drawn data should always carry a substantial error bar and note the high uncertainties.
Well it is time please that WUWT added
Viv Forbes
and
The Galileo Movement
to the link section.
http://www.galileomovement.com.au/
I know we are DOWN UNDER, and we did have the greatest industry in wool for there for a while, but now we Aussies need to show our tremendous work in the mining and agriculture sector + associated industries/workers for the many Australians, thank you. And IT.
one of the postulated mechanisms is that the sheep wipe out the herbs that compete with trees, thus stimulating tree growth. Craig Allan has written on this in connection with ponderosa pine. There were huge populations of sheep in some US areas in the late 19th century.
Well in Australia sheep don’t eat bark, goats do so do deer, and cattle will. I remember planting
100 pines and couldn’t understand where they all went. Dear little cattle. Possibly even rabbits
I don’t know but I was told to one should protect saplings from cattle? Who nose? LOL
Anyway ‘Hide the Decline’ is still on U Tube that ridiculed M Mann it is hilarious. Even though he
said he would sue them?
Once again we have what appears to be an outstanding feat of genetic hybridization, One that has seemed to become more popular and prevalent with each passing day. I speak of course of that malignant creature which results from the combination of DNA of the crocodile with the DNA of the abalone i.e. the infamous crocabalone.
While it may be possible to estimate the total number of herbivores in a given time period in a given area, it will never be possible to accurately state the number of herbivores in a particular area in a particular year. Beyond that, it will never be possible to determine whether ANY herbivores nibbled on the tree that you are sampling in any particular year.
While it may be possible for such a study to help more precisely define the error bars regarding a particular trees ring measurements, to state that this study helps them to define the data itself better is not supported.
Can’t provide another sheep pun – they’ve all been used up 🙂
Not sure if this has any relevance, but I have recently finished cutting up 18 – 22 year old rainforest acacia, cyclone damaged 3rd February 2011, at 19°11’38″S 146°40’31″E. Stand-alone trees, no herbivores, no additional nutrients, not much variation in solar here over their lifetime. Been monitoring precipitation since Aug 2004, average has been slightly above long-term average. No artificial irrigation anywhere near the youngest tree. The older tree was on imported salt-pan clay over dune sand, got to suck water from profligate irrigation next door, and has a trunk diameter at 1m of about 75cm. Younger tree is on old dune sand only. Trunk diameter at 1m is about 36cm. Last 7 years of tree rings show increasing width. If “as above so below” applies, the tree got to the ‘dry season’ minimum aquifer (6m down) by year 10 at the latest. So it looks like the latter 7 years growth could be enhanced CO2 ?
On the other hand, although we never irrigated near the tree or applied nutrients in the area, nutrient deposition would have been occurring throughout the period.
Dave Wendt says: July 27, 2011 at 4:27 am
…….. i.e. the infamous crocabalone.
Excellent. Do they design necklaces? And where can one purchase such?
There’s another really important finding in the abstract of this paper:
“Radial growth was negatively related to altitude and related to summer temperature in a nonlinear fashion, increasing from low temperatures and saturating and decreasing at high temperatures.”
Nonlinear response to temperature is a major problem for tree ring-based temperature reconstructions.