Is January too early to think about spring flowers blooming? According to a new scientific paper, we aren’t waiting as long for those first native wildflowers to bloom in Pennsylvania thanks to climate change.
Ryan Utz, Ph.D., an associate professor of water resources at Chatham University, and some colleagues used botanical records from over 100 years to explore how bloom dates have changed over time. The Allegheny Front’s Kara Holsopple recently spoke with him about it.
LISTEN to the conversation
Kara Holsopple: Your study is called “Are early blooming plant species more phenologically responsive?” So let’s just get the elephant out of the room. What is phenology?
Ryan Utz: Phenology is the concept of ecological events in the context of time. So a phenological event would be blooming, seeding, even emerging from the ground and producing leaves for the first time in a season. All of those are phenological events and you can tie a specific date to those events typically.
Kara Holsopple: What were you hoping to learn in this study?
Ryan Utz: We initially set out to just get a feel for the phenological responses of common Pennsylvania wildflowers to climate change over time and using herbarium records from the Carnegie Museum of Natural History. My colleague there, Mason Heberling, and I guided two Chatham University students to investigate that using very old herbaria records. We’re talking pressed plants from as early as the 1880s.
By looking at those pressed plants, and of course every museum record has a date stamped when the specimen was collected, we could time when those phenological events were happening. When each plant species was blooming. We could then tie that to a location because that’s another thing that is required of all museum specimens. So with those two bits of information, we could track over about a century and a half, how and when these wildflower species were blooming.
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Kara Holsopple: Tell me about some of the species of plants that you looked at.
Ryan Utz: The majority of species that we were looking at tended to bloom in the early to mid spring. So there were species of trillium, bloodroot, there were bluebells that we looked at – very commonly encountered wildflower species that you would see in Western Pennsylvania.
We also looked at some later blooming species that would bloom in the middle of the summer, like species of goldenrod or Joe Pye weed. So we had a good representation of many different plant families and many different blooming strategies in terms of when they send a flower out into the world, whether early spring, mid spring, or summer.
Kara Holsopple: And what did you find?
Ryan Utz: We found that, of course, a lot of flower species are blooming earlier, as we were expecting to, because climate change is causing the species to simply bloom at an earlier date. Things get warmer faster, and so the flowers can detect that and bloom earlier as a consequence.
[F]or early blooming species in the spring, almost all of them were blooming significantly earlier in the season, and by that, we’re talking more than two or three weeks than they were blooming in the 1800s.
But what surprised us was that there was a real temporal signal as to the severity of response to climate change.
It was the early blooming flower species, the very early things like trillium, like bluebells, that seemed to be really sensitive to climate change. They seemed to be blooming a lot earlier than species that bloomed in the middle of the summer, like Joe Pye weed, which really didn’t put out a signal at all.
We couldn’t find any trends of changing blooming patterns with summer blooming species, but for early blooming species in the spring, almost all of them were blooming significantly earlier in the season, and by that, we’re talking more than two or three weeks than they were blooming in the 1800s.
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Kara Holsopple: What are the consequences of that?
Ryan Utz: That remains to be seen. Another thing that was interesting in this study is that when we investigated other studies that had done similar work, we noticed that a lot of other people working in other places in the Northern Hemisphere, in Europe and North America, detected the same thing.
That is that earlier blooming species tended to be more significantly impacted by climate change than later blooming species. It’s just simply that nobody had ever synthesized that information before. So we think that it’s a widely occurring phenomenon across North America and maybe other temperate places around the world.
The consequences therefore need to be studied because this is sort of news in ecology, at least the sense that this is a very widely occurring phenomenon. So there could be many consequences. For instance, migrating bird species coming back from the south in the spring. They get here, they need to take advantage of fruit and insects and other things that are phenologically tied to plant blooming.
So of course, if a flower is blooming in the forest in early spring, it’s trying to attract pollinators. If the pollination and the pollinator are getting active earlier, they may miss the timing of the bird migration.
Kara Holsopple: You mentioned further study is needed. Tell me more about that.
Ryan Utz: We simply don’t know what the mechanisms are here. There are a lot of different ways that a plant may respond to its environment and do a phenological event, like blooming.
An early blooming spring species may be responding to leaves coming out in the canopy, more so than the temperatures. Or maybe they’re responding to snow melts. So every species of plant might have a specific mechanistic cue that causes it to flower. But what that is and if that is important in predicting how a plant species is going to respond to climate change, we simply don’t know yet.
It’s those early blooming species like trillium, bluebells, a lot of the species that are really celebrated around here for their beauty – for good reason – are those ones you’re going to start seeing earlier and earlier.
We also don’t if this is something tied to the evolutionary history of these plant species. Maybe certain families are simply more acutely sensitive to climate change compared to others. Or maybe it’s just that all of the species blooming during a certain season are uniformly or nearly uniformly sensitive to climate change over those that bloom in a different season.
Kara Holsopple: So your findings are similar to other studies on phenology and flowering?
Ryan Utz: Yeah, we looked at about 20 to 25 other studies that did similar work. I would say more than 90% of them tended to show the same sort of thing that we did. So studies up in Minnesota, New York, even those in Europe tended to show that earlier blooming species are more acutely sensitive to climate change. And that included studies that weren’t doing observational studies like ours using old herb area records, but rather experimental warming. We noticed some experiments that showed a similar sort of pattern.
Kara Holsopple: Those are experiments where people are growing plants in a lab?
Ryan Utz: Exactly. When a scientist controls the degree of warming and grows plants in a very managed setting, then we can also explore the same sort of question, which is really crucial because it takes all of these approaches to fully understand what is happening in an environment, both observational approaches like ours and experimental approaches that manipulate things like temperature or light, or thawing in a laboratory setting.
When all of those findings come together, then we can see a general picture emerging, if we’re lucky. The evidence in aggregate really seems to be coalescing around this idea that it’s those early blooming species like trillium, bluebells, a lot of the species that are really celebrated around here for their beauty – for good reason – are those ones you’re going to start seeing earlier and earlier.
Ryan Utz, Ph.D. is associate professor in the Falk School of Sustainability and Environment at Chatham University. He co-authored the paper published in Oikos with Hunter Holcomb, Searrah Bierker and J. Mason Heberling, Ph.D.
