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Science and Innovations

Drought Threatens Arizona’s Pinyon Pines

Melissa Sevigny

Some people collect pinyon pine nuts this time of year for a tasty autumn treat. Others sell them for extra income. But Catherine Gehring of Northern Arizona University goes nut-gathering every September for a different reason. She researches ways pinyon pines survive drought—at a time when a hotter, drier climate is predicted to drive the trees out of Arizona entirely. KNAU’s Melissa Sevigny spoke with her in the woodlands east of Flagstaff.

So you’re out here today collecting cones and this orange bucket I guess is your cone collecting kit.

Yeah, it’s a home depot bucket, but it’s a good way to put your field supplies for lots of things, so we often carry these buckets around. Today was just reconnaissance to see if it’s worth coming out to do any more collecting, and it doesn’t turn out to be a very good year this year, so all I had with me today was just gloves, because it’s a sticky work and you don’t want that resin on your hands if you can help it, and paper bags to collect a few cones in.

What do you hope to learn from collecting the cones?

In recent years we’re really interested in drought tolerance. We collect the seeds for that purpose, because we are trying to figure out if different maternal trees provide different levels of drought tolerance, and we already know that’s the case from some of our earlier studies. Then we can grow more of them to try to figure out the mechanisms, so we’re trying to understand how do these differences manifest themselves.

So what have you found so far about what makes a pinyon pine more likely to survive a drought?

Part of it is surprising, because we have these trees that we’ve seen and been studying and they had differences in the abundance of an insect that caused their architecture to shift. So if you have a lot of this insect, this moth, it basically trims the top of the tree and makes it a shrub, and it also reduces the number of female cones that it makes. When drought came in 1996—that was the beginning of our very dry time punctuated by these really extreme droughts—we thought that those susceptible trees to this moth that look shrubby and grow slowly would be the ones that would die. But it turns out the exact opposite happened.

This is still a bit of a mystery, this insect is harming the tree but also helping it get through droughts?

Right. It’s probably not the insect itself. What we think is happening is the insect is picking the most vigorous trees. What’s been interesting is the moth populations have dropped a little bit with the drought, and now it seems like the trees that were susceptible to the moth now are doing much, much better over the last 10 years than the ones that are resistant to the moth. It’s a real reversal of fortune.

Do you feel optimistic that a few tough trees will cling in there and hang on even if this drought continues?

Yes. I don’t like to look at the maps that show there’s no pinyons in Arizona in the future. I like to think there’s enough genetic potential in the survivors, so there will be some survivors that can handle the warmer, drier conditions. So that’s what we’re looking for is these ones that managed to survive when the others have died, and what is it about them that allows them to survive and will they ensure the future of pinyon pine.

Catherine thanks much for the field trip today, appreciate it.

Sure, you’re welcome. Thanks for coming along.

Melissa joined KNAU's team in 2015 to report on science, health, and the environment. Her work has appeared nationally on NPR and been featured on Science Friday. She grew up in Tucson, Arizona, where she fell in love with the ecology and geology of the Sonoran desert.
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