It is spring outside in Phoenix — but in a few days, it might not feel like it. Temperatures are forecast to hit triple digits by the end of the week.
It’s also been a fairly dry spring in the Valley. And while that has implications for a lot of aspects of the desert ecology, we’re going to focus on phenology — the study of the timing and cyclical patterns of events in the natural world. In other words, when do plants bud? When do birds come back? And when do flowers bloom? Basically, how springy is this spring?
Theresa Crimmins, associate professor in the School of Natural Resources and the Environment at the University of Arizona and director of the USA National Phenology Network, joined The Show to talk about what she is seeing as far as spring springing.
Full interview
THERESA CRIMMINS: It's kind of dull this year, honestly. I mean it's finally spring. Yes, I agree with you, it has arrived, but it's not the showy spring that we've had in some recent years. We are nowhere near a super bloom. It seems like a barely bloom, honestly, in my experience. And I think that has a lot to do with how dry it has been.
BRODIE: Yeah, I wanted to ask you some of the reasons for that. ... How much do you attribute it to the fact that, at least until somewhat recently, much of Arizona hadn't really gotten much rain?
CRIMMINS: Oh my gosh, no, we haven't. Our plants here are largely driven by moisture. And so when they don't receive adequate moisture, one of the ways that they respond is just by having a diminished bloom. There are fewer flowers produced, fewer flower buds produced. And they're slower to open. And then one of the other ways that we can really see the consequence of dry conditions is stunted growth, especially in annual plants.
So, a lot of those plants, when they do finally receive some moisture, will quickly germinate, but then also quickly flower and then go to seed. And so plants, grasses and other forms that sometimes are 6, 8, 12, 18 inches tall can flower when they're just a couple of inches tall. And I've seen that in a couple of places.
BRODIE: So what are the impacts of all this — beyond obviously the aesthetics? A lot of us like to see beautiful flowers sprouting up this time of year, but if that's not happening beyond just not being able to see it, why else does that matter?
CRIMMINS: Well, a lot of insects and birds and other species, like bats, rely upon flowers for food sources, primarily. And so when we have less of that available, it's just a little harder for them to find the resources that they need, and we can have a bit of a ripple effect. Epecially in those short-lived species, where their population numbers can be decreased as well. Or they may have to pivot to an alternative food resource if the particular species that they prefer are available, readily for providing nectar.
Also, one good consequence, I guess you might say, is if we have fewer annual plants coming up because it's dry, Homeowners might be relieved that they have fewer weeds to pull. I haven't had anything that I've needed to do in my yard this spring. And it's kind of a double-edged sword for wildfire. It's less finer fuels that might carry a fire. However, the lack of precipitation results in much drier vegetation for the plants that are out on the landscape, and so that can increase risk. So it kind of cuts both ways there.
BRODIE: In terms of what we're seeing now, does that tell us anything? Or is this a sign of anything to come botanically or ecological wise for the next little while here?
CRIMMINS: I guess one consequence when you have fewer flowers being produced is that you have fewer seeds being produced in this particular season. But seeds are generally long lived in the soil. They can exist years, sometimes decades, even longer, so there isn't really a huge risk from that perspective. And whether this is likely to have long-reaching changes, long-term changes, it's probably not. Iit's really more about probably if we keep having dry seasons one after another, that starts to really take a toll. That definitely takes a toll on all the plants. And so I don't know actually what the long-range forecasts are, but I sure as heck hope we get some decent rain this monsoon because the plants are pretty dry.
I see in my neighborhood, the cholla cacti that usually are upright and rigid are rather droopy. And that's a sad sight to see. I see a lot of creosote that look pretty darn rough. That's a very robust shrub that's really drought tolerant, and they can spring back. They can look terrible. And then finally, when they finally receive some rainfall, they will flush with green leaves and come back from basically what they look like are dead and fill out with flowers. So we haven't been pushed past any threshold, I don't think at this point. But we could definitely benefit from seeing some moisture.
BRODIE: Yeah, I wonder if there's sort of a balance that you're looking for here in terms of precipitation and temperature. Because I would think having a spring that is springing too early — maybe because it's warmer than average like in January and February and plants and flowers think, “Oh, it's time to go,” when in fact it's really not. I would think that would be a problem. But as you're saying, the fact that there's very little precipitation and we're kind of having a “meh” bloom this year and things just aren't that exciting, maybe also isn't ideal. Is there really like a happy medium you're looking for here?
CRIMMINS: I think the plants just want water, honestly. Yout know? So when I look at the temperatures, I'm looking at it through the lens of how plants perceive temperature. And so it's really kind of less about long-term average or seasonal average or monthly average temperatures. It's more about how much warmth have they been exposed to, because that's usually what triggers their activity. And when we look at the rate of warmth being accumulated here in Arizona this year, it's pretty average, honestly. So I really think that we haven't had an extra warm set of conditions. ... I think it really has so much to do with the moisture.
If we do have those really warm years and there isn't moisture, then that creates even additional stress, for sure. And so if we see increasing temperatures — and even just average precipitation — that can still be hard on plants. If we see increasing temperatures and less precipitation, that's definitely really, really hard on them, and there are limits.
There are definitely physiological limits that we may be starting to dance with when we look at how things are trending over the long term. But I don't know that we're really flirting with that right this second.
BRODIE: OK. What is the significance of tracking this kind of thing? Even as you said in a spring like this, a season like this where it's not really remarkable, it's kind of a thing that's happening like it happens a lot. Why is it so important to continue to track this stuff?
CRIMMINS: Every observation that we make is a data point that can help us better construct a picture of what's happening both across the whole landscape and among all the different species. As well as whether there's any underlying temporal trends.
... We're talking in generalities right now about how plants tend to respond to this condition and that condition, but it's a very individualistic set of conditions. Every species really responds in different ways to different things. And largely scientists don't understand that to a great degree. And so the more information we have, the better we can disentangle that — and the better we can understand how things might be expected to change and how we might do the best job we can at facilitating their continued existence and persistence on the landscape.
BRODIE: All right, that is Teresa Crimmins, an associate professor at the University of Arizona School of Natural Resources and the Environment, also director of the USA National Phenology Network. Teresa, nice to talk to you. Thank you.
CRIMMINS: Thank you so much.
