Story of the Week: Sheep Tweak Tree Ring Data

<a href="http://www.flickr.com/photos/scottstgeorge/3354949324/">Scott St.George</a>/Flickr


Precipitation, elevation, and even cloud-cover affect tree ring growth, but now there’s another factor for scientists to consider: sheep. A new (ewe?) study out of Norway shows that the number of livestock in an area affect tree rings more than temperature.

The study compared 206 birch trees growing in Norway for 9 years at three different levels of sheep density: no sheep, 25 sheep per square kilometer, and 80 sheep per square kilometer. Researchers found that the more sheep around, the slimmer the tree rings. Trees that grew up in a sheep-less environment had rings three times wider than the trees that grew up around the most sheep.

This isn’t to say that all tree ring data used to estimate past climatic conditions is invalid, but it is another element to factor in. Study lead author James Speed said, “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.”

So, basically, next step: study shrooms that grew on sheep poop centuries ago. Sounds exciting. Until then, the sheep study will likely give fuel to those who maintain that tree ring data are not a reliable indicator of climatic history, despite the fact that scientists also use things like coral records and ice cores to estimate past temperature changes. As Mother Jones has reported in the past, sometimes the controversy has come from very particular tree ring data sets calculated in scientifically unsound ways. If nothing else, this study involving sheep has uncovered a way to make tree ring data more accurate. Whether climate skeptics will see this as a positive or a negative is up for debate.

 

MORE HARD-HITTING JOURNALISM

In 2014, before Donald Trump announced his run for president, we knew we had to do something different to address the fundamental challenge facing journalism: how hard-hitting reporting that can hold the powerful accountable can survive as the bottom falls out of the news business.

Being a nonprofit, we started planning The Moment for Mother Jones, a special campaign to raise $25 million for key investments to make Mother Jones the strongest watchdog it can be. Five years later, readers have stepped up and contributed an astonishing $23 million in gifts and future pledges. This is an incredible statement from the Mother Jones community in the face of huge threats—both economic and political—against the free press.

Read more about The Moment and see what we've been able to accomplish thanks to readers' incredible generosity so far, and please join them today. Your gift will be matched dollar for dollar, up to $500,000 total, during this critical moment for journalism.

We Recommend

Latest

Sign up for our newsletters

Subscribe and we'll send Mother Jones straight to your inbox.

Get our award-winning magazine

Save big on a full year of investigations, ideas, and insights.

Subscribe

Support our journalism

Help Mother Jones' reporters dig deep with a tax-deductible donation.

Donate

We have a new comment system! We are now using Coral, from Vox Media, for comments on all new articles. We'd love your feedback.