Is Spring Falling Out Of Sync?

17:01 minutes

pink plum blossoms peak out from beneath melting snow on a branch
Credit: Shutterstock

Each year, it feels like spring comes as a surprise—too early or too late. For example, new maps reveal that spring is 13 days late in Sacramento, California but two weeks early in Richmond, Virginia. And that could be a problem because plants and animals use environmental cues, like temperature, to know when to flower, migrate, breed, or emerge from hibernation.

So when the seasons are thrown off, what happens to those natural rhythms that once flowed together seamlessly? Guest host Shahla Farzan talks with Dr. David Inouye, professor emeritus at the University of Maryland and a researcher at the Rocky Mountain Biological Station, and Dr. Theresa Crimmins, director of the USA National Phenology Network and research professor at the University of Arizona. They discuss the variability in seasons, and the cascade of effects these changes can have on ecosystems.

An animated map shows that spring is becoming earlier for more of the southeast united states each year, and later for the southwest united states each year
Spring first bloom index anomaly. Spring bloom has also arrived in southern states, days to weeks early in the Southeast, and days to over a week late in the Southwest. Credit: USA National Phenology Network, University of Arizona, www.usanpn.org

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Segment Guests

David Inouye

David Inouye is a professor emeritus at the University of Maryland and a principal investigator at the Rocky Mountain Biological Station in Paonia, Colorado.

Theresa Crimmins

Theresa Crimmins is director of the USA National Phenology Network and a research professor at the University of Arizona in Tucson, Arizona.

Segment Transcript

KATHLEEN DAVIS: This is Science Friday. I’m Kathleen Davis.

SHAHLA FARZAN: And I’m Shahla Farzan. OK, Kathleen, I live in St. Louis, Missouri. And here, the magnolia trees and daffodils and witch hazel all started blooming weeks ago. And I am once again amazed, but also not surprised by just how early spring has sprung this year.

KATHLEEN DAVIS: Yeah. I’m seeing cherry blossoms and crocuses here in New York City. But spring looks very different across the US. Our listener Chris in California’s Sierra Nevada mountains sent us a voice memo.

CHRIS: We are surrounded by 4 and 5 and 6 feet of snow still. And I hear people other places talking about flowers and pollen and the signs of spring, but we have not seen that here.

KATHLEEN DAVIS: But for Melissa in the Hudson Valley, spring is here.

MELISSA: My forsythia plant is blooming and it’s March 24. Pretty sure that’s a record.

SHAHLA FARZAN: As ready as I am for winter to be over, and I am definitely ready, this is also concerning. All of these different plants and animals basically have a built in clock that tells them when to migrate and breed and bloom, you know, important seasonal activities. And for a lot of species, climate change is messing with that clock. It’s called a phenological shift. And scientists are trying to figure out what these could mean for the future.

Joining us to talk about that are Dr. David Inouye, professor emeritus at the University of Maryland and a researcher at the Rocky Mountain Biological Laboratory. He’s based in Paonia, Colorado. And Dr. Theresa Crimmins, director of the USA National Phenology Network and professor at the University of Arizona based in Tucson. Welcome to Science Friday.

DAVID INOUYE: Thank you.

THERESA CRIMMINS: Thank you, Shahla.

SHAHLA FARZAN: So David, let’s start with you. You’ve been working in Colorado’s high alpine meadows for the past 50 years. Could you describe that environment for us? What does it look like, for people who haven’t been there?

DAVID INOUYE: Well, the Rocky Mountain Biological Laboratory is situated at 9,500 feet in the West Elk Mountains of Colorado. So it’s in the East River Valley. And the lab’s in the valley bottom. And we look up at the mountains surrounding us, that 13,000 foot peaks.

And it has a relatively short summer. So right now there’s about 90 inches of snow on the ground. And it’s going to be a little while before that melts and the road opens. But it will be a very busy summer once the snow melts and all of the phenological cues that trigger flowering and activity of pollinators and herbivores commence.

SHAHLA FARZAN: So speaking of which, you and your collaborators have collected one of the longest running and most detailed data sets out there on these alpine ecosystems. Why did you start doing this in the first place?

DAVID INOUYE: There were a group of us who were all graduate students working at the biological lab in the early 1970s. And we were interested in pollinators. Some of us were working on hummingbirds. Some of us working on bumblebees. Some on butterflies. And we decided we wanted to learn more about the floral resources that those pollinators depend on.

So we each picked a habitat, and we each went around and set up some 2-by-2 meter plots. And then for the rest of the summer, we went around and counted every flower that bloomed in those plots. And at the end of that season, we had some very interesting data. But it seemed like it might be interesting also to find out how different is it from one year to the next. So we continued that for a second year.

And at that point, most of my collaborators had the data they needed and stopped counting their flower plots. But for whatever reason, I decided to keep my plots going and picked up one other set of plots. And 53 years later, we are still counting those flowers.

SHAHLA FARZAN: So how many records so far do you think that you’ve counted in those 53 years?

DAVID INOUYE: Oh, we have counted millions of flowers because of the fact that we’re counting up every flower of about 130 different species and doing that every other day or three times a week for the whole growing season. So those numbers add up quickly.

SHAHLA FARZAN: I bet. So in the many decades that you’ve been working there, have you noticed shifts in timing with your own eyes?

DAVID INOUYE: Yes, definitely. The phenology at that altitude is almost entirely set by when the snow melts. So that determines the beginning of the growing season. It determines when the migratory species move in, when the species that are hibernating underground emerge from their winter hibernation.

So the snow melt date has been changing, partly because we’re getting typically less snow than we used to and it’s melting earlier than it used to. So that starts the whole phenological clock earlier. It used to be that we could pretty much count on seeing the beginning of flowering, if I got there at the end of May. But now, by the middle of April, on south-facing slopes, we sometimes have flowering.

SHAHLA FARZAN: So we’ve been talking about the shifts in timing that you’ve been seeing in the alpine environment, David. But, of course, this is happening all over the world, not just in this ecosystem, right?

DAVID INOUYE: That’s right. I think anywhere in the world that you look, the seasonality is changing. And it’s changing at different rates in different places. So that causes problems, for instance, for migratory species, like the migratory hummingbirds that are overwintering in Mexico are using some cue, presumably an environmental cue, for when to begin their migration north to their breeding grounds.

But that cue may not be changing at the same rate as the cues along the way, like the flowers that they’re going to be visiting in Arizona, perhaps near Theresa, and not at the same rate as the flowers that are up in Colorado where they’re going to be reproducing for the summer. So those differences over time and space are creating problems for a variety of species.

SHAHLA FARZAN: Right. Theresa, as we mentioned, you’re the director of the USA National Phenology Network, this giant database that keeps track of the timing of plants and wildlife and seasons. Why is tracking that kind of information important?

THERESA CRIMMINS: I think David did such a fantastic job illustrating that. It’s really the repeated observations, when you have information on what’s happening and when it’s happening at a location or even on an individual plant from one year to the next, that’s where you can really start to see whether things are changing.

There is very often a lot of variability from one year to the next in terms of the timing and when plants or animals undergo their transitions. But when you can look over many years, you can start to see is there also some sort of temporal shift layered on top of that year to year variability. And that’s what our network is really intended to help us understand.

SHAHLA FARZAN: How are those data collected for the network?

THERESA CRIMMINS: We rely on the power of volunteers, basically. We have thousands of very dedicated individuals, both professional scientists and volunteer scientists, all across the whole country who very graciously dedicate their time and talents and make repeated reports on what they’re seeing happening in plants and animals in their yards.

SHAHLA FARZAN: The power of citizen scientists. I love it. So what are we seeing this year in the US in terms of spring timing?

THERESA CRIMMINS: This year’s been an interesting spring. [LAUGHS] We had a pretty standard start to things at the very beginning of the year. Nothing really started anomalously early down in Florida. But once we started to hit February, things really picked up in much of the Eastern US.

Southeastern and Eastern US experienced a really mild winter and then a lot of warmth very early in the year. And as a consequence, leaf-out and flowering activity and activity in some early spring animals and insects has started, in some cases many weeks earlier than average in the Eastern US.

And then the flipside of that is that it’s been cooler than average in much of the Western US. And so we are having a slower start to spring here in Arizona where I’m at and in some of the Western states.

SHAHLA FARZAN: David, you alluded to this a little earlier. But what happens when plants and wildlife shift their timing? Let’s say a plant blooms early. What kind of chain of events can that set off?

DAVID INOUYE: Well, for instance, let me use the glacial lily, erythronium grandiflorum, as an example. Some of the earliest individuals to bloom are flowering before the bumblebee queens emerge from underground, and those are the primary pollinators.

And so although both species are now starting their seasons earlier than they used to, they’re not changing at the same rate. So the earliest glacial lilies to bloom are not getting pollinated. And that kind of mismatch is something that we see between the flowers and the migratory hummingbirds as well.

SHAHLA FARZAN: Yeah, it sounds like what’s tough here is that not every species is responding in the same way here. So maybe some are shifting their timing by a couple of days, maybe some are shifting by a month or not shifting at all. Is that what makes this hard to really wrap your arms around and understand?

DAVID INOUYE: It makes it a little bit difficult to study. Perhaps makes it also more interesting because it means you can’t generalize. For instance, we have found, through looking at different bumblebee species, that they’re not all responding in the same way. So we can’t even say, well, here’s what happens to bumblebees. We have to say, well, here’s what happens to bombus appositus or here’s what happens to bombus flavifrons.

SHAHLA FARZAN: Theresa, are there certain kinds of species that maybe we would expect to be at higher risk from changes in timing generally?

THERESA CRIMMINS: Oh, that’s a really good question. There are different cues that drive the start of activity in different plants and animals. In a lot of species in the springtime, it has to do with how much warmth they’ve been exposed to. But sometimes it also has another important key ingredient is how much chill they’ve been exposed to. Other species are very sensitive to the amount of light, and so even if it is warm, they won’t respond if the days aren’t long enough.

Where we really do start to see mismatches emerge, like what David has been describing, is when you have two interacting species that respond to different cues. And so if you have, for example, a species that’s really mostly responding to day length, that species is not likely to be changing the timing of its activity very much because day length is a fixed parameter from one year to the next.

And in contrast, temperature is very much variable from year to year, and that is where we are seeing these trends. And species that are mostly responsive to temperatures are the ones that we are seeing some of the greatest advancements in. And so species that are the most likely to be vulnerable are those that are both showing big changes and where they are dependent upon another species and that species is not changing. So where mismatches are beginning to emerge.

SHAHLA FARZAN: So it sounds like there’s kind of this whole suite of different cues that species may be responding to. So it may not necessarily just be temperature then.

THERESA CRIMMINS: Absolutely. And honestly, that’s a very active area of research. We know in broad brush terms that these factors play a role in shaping when species undergo their different activity from one year to the next. But when it comes down to specific species, in a lot of cases we don’t really know the exact cues.

And so that’s one of the reasons why our network exists. Those data that are being contributed by volunteers across the whole country are actively being used by researchers to try and disentangle and better understand what those cues are so that we can better understand and anticipate where mismatches might start to emerge, which species may be more vulnerable going into the future, and hopefully what we can do to prevent major problems.

SHAHLA FARZAN: This is Science Friday from WNYC Studios. I’m Shahla Farzan, talking with two researchers about the effects of spring springing earlier.

David, when we talk about these tiny changes over a long period of time, it can be kind of hard to feel them, right? I’m imagining a lobster slowly being boiled in a pot of water. And some of the big challenges for us are what we often refer to in ecology as this idea of shifting baselines, right?

What we think is normal today, maybe is very abnormal compared to what we would have experienced 40 or 50 years ago. But it seems like these long data sets or large data sets like you’ve collected can help alleviate that a bit. Is that right?

DAVID INOUYE: I think they’re actually essential for gaining an understanding. The high altitude area where I work is very variable from one year to the next. This year we have a way above average snowpack. Last year it was way below average. And I couldn’t do very much with two data points given that kind of variation. So I really needed to have 10 years of data before I could begin to see trends.

One of the projects I looked at was what triggers flowering by a particular species of plant that doesn’t bloom very often. And it took me close to 30 years of data points before I had enough data points to be able to pick out a trend amongst all the variability.

SHAHLA FARZAN: So David, you have dedicated your career to studying these alpine meadows in Colorado. And as you mentioned, you’ve seen them change a lot over the course of your career. What are some of your big concerns moving forward?

DAVID INOUYE: Well, I guess one of my concerns is how rapidly things are changing. We’re seeing new species moving up to the altitude of the biological lab. We didn’t used to have foxes there or moose there. But they’re now there year-round. There’s a new species of mosquito that’s appeared, a new species of ground squirrel that’s moved up in altitude.

So there are all these changes occurring in the plant and animal communities because of the ongoing climate change. So the world is going to look very different in the future from what it does now. And I think that’s one reason for why it’s important to be trying to document what is the community like now and what’s changing about it.

SHAHLA FARZAN: I can imagine it must be pretty hard to watch this place that you really love change a lot and change in very obvious and visible ways.

DAVID INOUYE: Yeah, it is difficult. I’m fortunate to have some family members who also do research with me now. My son and his wife are both collaborators and now taking the lead on some of this long-term phenological research. And their daughter, my granddaughter, spends her summers out there. And I think it’s fun to show her the ecology of this area. But what she experiences when she’s my age now is probably going to be very different from what she’s seeing now as a teenager.

SHAHLA FARZAN: Yeah, I can imagine that. Theresa, you said earlier that the phenology network depends a lot on community scientists to contribute. So how can somebody get involved if they’re interested?

THERESA CRIMMINS: They can come to our website, usanpn.org. And we’ve got all the information that it takes to get started as an observer in nature’s notebook. There’s a list of over 1,700 species of plants and animals that are available now to observe.

And basically, what it entails is registering yourself as an observer, choosing a site where you’re going to make repeated observations– so we strongly encourage for that to be something that’s very accessible, like your own yard– and then identifying one or more of the plants or animals that you would make repeated observations on.

And then you become acquainted with the questions that you would be responding to each time that you’re making an observation. And you can do that either via paper data sheet or through our app called the Nature’s Notebook app.

SHAHLA FARZAN: Great. And we should mention here that if you, listeners, would like to get involved with this kind of research, we’ll link to some of those citizen science programs on our website. That’s sciencefriday.com/spring. And I think we’re going to have to leave it there.

Thanks so much to my guests. Dr. David Inouye is a professor emeritus at the University of Maryland and a researcher at the Rocky Mountain Biological Laboratory. He’s based in Paonia, Colorado. And Dr. Theresa Crimmins, the director of the USA National Phenology Network and research professor at the University of Arizona in Tucson. Thank you both so much for joining me.

THERESA CRIMMINS: Thank you, Shahla.

DAVID INOUYE: Thank you.

SHAHLA FARZAN: And a springtime program note. Are you a stem educator? Citizen Science month is coming up this April. And it’s a great opportunity to get out and do some real world science with kids. So check out sciencefriday.com/citizenscience for more information. That’s sciencefriday.com/citizenscience.

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About Rasha Aridi

Rasha Aridi is a producer for Science Friday. She loves stories about weird critters, science adventures, and the intersection of science and history.

About Shahla Farzan

Shahla Farzan is a science journalist, PhD ecologist, and editor with American Public Media, where she helps produce science podcasts for kids. She loves showcasing the many weird and wonderful aspects of science—and encouraging young, curious thinkers to question and explore the world around them.

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