Higher Temperatures May Be Behind Pine Growth

Ancient bristlecone pine trees found in certain parts of California and Nevada have been growing at an unprecedented rate in the last 50 years. According to a recent study, this growth has most likely been caused by warmer temperatures. Malcolm Hughes, one of the study's lead researchers and a professor of dendrochronology at the University of Arizona's Laboratory for Tree-Ring Research, offers his insight.

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MELISSA BLOCK, host:

We may think of climate change killing off species or destroying habitat. Now, a twist: Tree researchers studying bristlecone pines in California and Nevada have found those trees growing over the last 50 years at a faster rate than at any other period in the last 3,600 years. They were looking at trees at an elevation of almost 12,000 feet at the upper tree line.

Malcolm Hughes has been studying those pines, which can be up to 5,000 years old. He's a professor of dendrochronology at the Tree-Ring Research Laboratory at the University of Arizona.

Welcome.

Professor MALCOLM HUGHES (Dendrochronology, Laboratory for Tree-Ring Research, University of Arizona): Thank you.

BLOCK: And first, give us a picture. Describe this bristlecone pine tree. What does it look like?

Prof. HUGHES: They almost look like slightly enlarged bonsai. They are very twisted. They're growing in very tough environments. They may not be much more than 15 feet tall but rather wide with multiple stems, and they're really quite spectacular to look at.

BLOCK: Okay, well, you've been looking at the rings of these bristlecone pines to chart the growth. What do they show?

Prof. HUGHES: In the last few decades, they're getting fatter rings than they've had for about 3,600 years. This is a very unusual event. It exists only in the trees near their upper limit, not in the trees just a few hundred feet lower down the mountain. So the mystery was why on earth is this happening?

BLOCK: And how have you resolved that mystery, or have you?

Prof. HUGHES: It was early a thought, 20 or so years ago, that this was probably mainly the result of there being more carbon dioxide in the atmosphere. Our results concerning the pattern of where the trees are going faster and where they are not is not consistent with that explanation, and that leads us to look for another explanation. The most likely one is the increase in temperature that has taken place over the 20th century for whatever reason, and we've got some evidence that strongly suggests that that's a big part of the story.

BLOCK: So boil that down for us. What do those conclusions lead you to understand?

Prof. HUGHES: We think that temperature is a big part of this change in the high mountains. It's one of many other changes in the high mountain environments that we're learning about that have taken place in recent decades, shifts in the zones where different plants and animals live, changes in the seasonalities, snow melt coming a week or two earlier in much of the West, even flowers of various species known to come into flower or to leaf earlier. Now, in the last few decades, things are different.

BLOCK: Does it give you any kind of thrill still, as much as you've done this, to be looking at a sample of a tree that might be thousands of years old?

Prof. HUGHES: Absolutely. It's really just always a wonderful experience. First of all, it's a remarkable thing that they're there and that they're still alive. And then also, of course, to think what else was going on when this ring was growing because after all, what we've got there is a little time capsule each year with the carbon, hydrogen, oxygen that were in the air and in the ground at that time captured and stored in almost perpetuity.

BLOCK: Well, Malcolm Hughes, thanks for talking with us.

Prof. HUGHES: My pleasure. Thank you very much.

BLOCK: Malcolm Hughes is a professor of dendrochronology - I love saying that, dendrochronology - at the Tree-Ring Research Laboratory at the University of Arizona.

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