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As species shift ranges in response to climate change, computer models struggle to keep up

A green pinyon pine tree at the edge of the Grand Canyon, with a blue sky
Grand Canyon National Park

Plants and animals are beginning to shift their ranges as the climate heats up. But computer models that forecast the future may be underestimating how many species are at risk of extinction. KNAU’s Melissa Sevigny spoke with Emily Schultz of the University of Nevada-Reno, who researched the fate of piñon pines in the Four Corners region.

What inspired you to do this research?

This research was inspired by trying to make better predictions about how species are going to respond to climate change… If we want to be able to make these predictions about how species might shift, we first have to understand, what it is that determines where we find species to begin with.

So you used the piñon pine as the target species to study. Why did you choose the piñon?

piñon pine, in particular, is an interesting species it’s really at the edge of the biome. If you get any hotter and drier, you’re getting into desert…. And piñon is known to be sensitive to climate, so we’ve already seen some big die-offs as a result of things like droughts.

So how did go about answering this question of where the piñon was and what was going to happen to it with climate change.

These data that were collected by the Forest Service as part of the Forest Inventory and Analysis program…. and then we used climate change to see how climate variabilities like temperature and precipitation…. We put all that together to calculate the population growth rate, which tells us if we’d expect to see the populations growing or declining or staying stable, and then we compared the results from that model to the actual distribution of piñon.

What did you find out?

When we looked at the lowest elevations where we found piñon pines, the hottest and driest areas, we predicted the species would not be able to persist in those locations. So even where we see that species now, we predicted negative growth rates… That suggests the trees in those areas are living on borrowed time, they’re probably already in locations no longer suitable to them, they’re getting too high and too dry. But the other thing that was notable, our model predicted we should be able to see these species at higher elevations, where it’s cooler and wetter, even in the presence other trees like ponderosa pine and Douglas fir. That told us that something was missing from the models that only look at the direct effects of climate and competition on piñon pine…. Climate can also affect things like the fire regime in an area, how frequent and intense are those fires…. When you have frequent fires in the system, piñon pine isn’t able to persist in those areas.

So if you were just looking at the climate, you’d see that the piñons were moving up in elevation, moving to cooler areas, but because there’s all these other things going on, like fire and competition, they aren’t necessarily able to do that.

Exactly, and most of the models we currently use to predict shifts in species distributions are only looking at those direct effects of climate. We might be underestimating how much range or how much the distribution species might lose if we’re also looking at these indirect effects.

And we’ve been talking about things that are already happening, so this isn’t something we have  a whole lot of time to work on, in that right?

Right, yeah… I think that’s one of the big challenges we have, especially with this finding that we need more complex models, and that requires a lot of data. Is there some way we can use really detailed data that we might have for some species, to generalize to what might be going on with larger sets of species?

Emily Schultz, thank you so much for speaking with me.

You’re welcome, thanks for having me.

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.