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Hit the Lights! The impacts of Artificial Light on Ecosystems with Garden Futurist Shannon Murphy

Articles: Hit the Lights! The impacts of Artificial Light on Ecosystems with Garden Futurist Shannon Murphy

Winter 2023

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This is a really special time of year and at Pacific Horticulture we are attempting to connect with nature in a way that may feel a bit off-kilter to many of us gardeners- we are embracing the darkness!  

Helping to introduce this topic, we have Katherine Renz, author of the recent article “The Night Garden: Design for Pollinators and People that Thrive Under Dark Skies.” 

We spoke with Dr. Shannon M. Murphy Professor at Department of Biological Sciences, University of Denver about her research on the impacts of artificial light at night on moths, herbivorous insects, and invasive plants and how gardeners can help support ecosystems at night.

This article was sponsored by:

Sarah Beck: You’re listening to Garden Futurist. I’m Sarah Beck. This is a really special time of year, and at Pacific Horticulture we’re attempting to connect with nature in a way that may feel a bit off kilter to many of us gardeners. We are embracing the darkness.

Here with me to introduce today’s guest is Katherine Renz. She’s the author of our new article, “The Night Garden.”

When we first talked about the idea of doing a darkness theme. I thought to myself, “I am not really a darkness person.” I know that most gardeners are also not darkness people, but I have to say that I feel like I have gotten into the spirit of this theme.

I’m just wondering what your response now is to this idea of thinking of darkness as part of nature now, as opposed to when you first started working on this article?

Katherine Renz: At first, I was thinking more design elements and different techniques and strategies, which we do touch on in the article—and I think it’s totally important. But like my own relationship with the dark, there’s kind of our cultural relationship and our physiological as diurnal creatures with pretty poor night vision compared to a lot of other animals. The majority of animals are nocturnal or do the dawn-dusk crepuscular thing.

So philosophically and culturally, our human weird relationship with the dark, and then realizing as I was trying to write these passages about communing with the nighttime and being like, “I’m never in the dark dark.”

Sarah Beck: I did want to ask you about whether you actually took that night hike to see arachnids.

Katherine Renz: I did. It was incredible.

Sarah Beck: What was that like? What happened?

Katherine Renz: The naturalist that I was with, one gentleman was expert at picking up scorpions.

So that’s something to think about for the oak woodlands and redwood forests. There are indeed—I’d always heard that there were scorpions and there are. They’re harmless, less than a bee sting, but what’s really cool is when you shine these UV flashlights on them, they fluoresce. So instead of being this chocolatey brown that totally blends in with the rotten logs and everything and the leaf litter, they fluoresce a sort of icy neon blue—aqua. I mean, at one point he shone his UV flashlight over the bank cutout from the trail, you know? There were probably eight of them there that you would never notice in the daytime or even really at night.

Sarah Beck: Oh, that’s amazing.

Katherine Renz: Connecting that idea of getting out and seeing these things that we don’t normally see—these creatures we don’t normally see, and other lifeforms—in ways we don’t normally see them because of our limited visual capacity, and then connecting that with the idea of embracing this season.

In a sense, I came to a conclusion during all this gathering research that nighttime is one of the last wild places. It’s accessible to almost all of us if we can get out of a place that’s permanent skyglow. We don’t have to drive to Yosemite or to the back country or take a flight to Tibet or something. Like we can just stay up at a time and be out at a time when a lot of humans aren’t out and there aren’t a lot of cars with headlights.

So that’s really neat. It’s almost an equal opportunity experience. Not quite. And it’s wild.

Sarah Beck: I love that. That’s a really nice insight.

I really loved how you cultivated in your article this appreciation of moths and you use butterflies as a contrast example, because I think there is perhaps a tendency for people to think of moths as maybe the less exciting, duller version of a butterfly, but that is not so.

Katherine Renz: Moths are incredible animals and incredible pollinators, too.

And none of this is to knock on butterflies. I love the butterflies, right? but there are 15 times more moths than there are butterflies, species of moths. So just by sheer numbers, the pollinating capacity of the work that they do is amped up, right? Yet about a third are severely endangered and the science is pretty new. Only over the last maybe 10 or 15 years have people really been studying moths and how light pollution is affecting them.

Sarah Beck: This is really a great point to make and it’s really exciting that we got a chance to talk to a scientist whose research is very broadly ecologically focused, but really, moths are a big component of that research.

We spoke with Dr. Shannon Murphy about her research on the impacts of artificial light at night on moths, herbivorous insects, and invasive plants. Dr. Murphy is a professor at the Department of Biological Sciences at the University of Denver.

Sarah Beck: I just want to start by asking you, are you a night person?

Shannon Murphy: No, not at all. I used to be, when I was a grad student. I’d stay up really late working every night in the lab, but ever since I had a child, that’s over, and if it were socially acceptable to go to sleep at 7 p.m., that would be me.

Sarah Beck: I can totally relate.

Although I have to say, this is my unscientific polling, but most people that I’ve ever interacted with in the garden and horticulture industry, I mean, we’re talking about morning people, generally.

So in a way, it’s really interesting at this time of year, because I’m noticing I actually experience the night more, the darkness more. It’s getting dark in the early evening and I might still be outside and I’m looking a little bit at the sky, or very early in the morning. I’ve had some mornings very early recently where, yeah, I was really enjoying seeing planets and the moon. It’s so beautiful.

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As we’re thinking about the fact that light pollution has negative impacts on many organisms, starting from this idea that, okay, light pollution can be a problem, I’m just wondering if you can give us some orientation as to how long research around this has been going on.

I totally had this memory the other day of, maybe it was a National Geographic years ago, when they first started getting those really great satellite images and you could see, “Oh wow, everything’s so lit up.”

Shannon Murphy: I don’t really know exactly when people started pursuing it as a dedicated area of research, except to say that it really has seemed to ramp up in the last 10, 15 years. Because when I first started here at DU, it was harder to find a lot of research on light pollution, that was almost 15 years ago.

There were a lot of papers, it was interesting, that were about what wavelengths of light to use to attract insects.

So we as insect ecologists use a lot of light traps as ways to catch nocturnal insects and moths. And it was interesting to see how papers from the ‘60s and ‘70s were, “How do I attract more insects to my light trap and what frequencies of light would be more attractive to those insects?” And now I think the research has completely shifted of, “How do we create lights that don’t attract insects or how can we avoid that?”

There’s lots of research looking at how lights along coasts were damaging to sea turtle populations. And I think that really started to ramp up in the ‘90s, but I would say that for insects, it’s like the last 20 years, maybe, at max, that people have been really thinking about it for problems with conservation. The last 10 years, it’s really ramped up.

And I think the whole idea of the insect apocalypse that people started worrying about in the late 2010s is really when we started thinking, “Oh. There’s probably a lot of problems out there, not just light pollution.” Temperature, heat waves, sound pollution, nutrient pollution, and light pollution.

And it seems to me that the field is growing almost exponentially right now.

Sarah Beck: That’s fascinating. You’re really in a new frontier of a field, it seems like.

Shannon Murphy: It is. It is exciting that we’re learning so much. Unfortunately, what we’re learning is how bad it is for insects, but it is exciting to be in a field where we’re discovering new things.

Sarah Beck: I want to mention that gardeners have such an interest in this topic now. Thinking about supporting food webs within a garden is really important to a lot of people. I’d like to ask you about your most recent publication, which is a really exciting paper: “Does artificial light at night alter moth community composition?” And so going into this research, I’m just curious what impacts you’re investigating.

Shannon Murphy: When we first went into it, I had a graduate student start with me in 2010. He was really interested in moth communities and also light pollution.

And we thought this would be really interesting because the research that was out there about light pollution and insects was actually, surprisingly, not really about moths when we started it.

What we were also interested in, though, is teasing apart the effect of direct street lighting—so the direct effects of the streetlight near where the moths are living—and what we call skyglow.

So skyglow is the effect of light pollution that’s like an indirect light source. And I think the best way to think about it is if you go out on a winter evening outside your house—even if you’re not in the city, usually there’s some skyglow going on—and if it’s cloudy, it all looks a little orange. It almost feels sometimes almost like daylight, even though you might not be near any streetlights. And that’s skyglow. And so that type of light pollution affects people who aren’t even in cities. If you’re even near a city, you’re probably getting some of that.

We were studying shortgrass steppe prairie fragments that are left over in the cities of Denver and nearby.

My student—her name was Kylee Grenis—she was amazing, and she very industriously set up this experiment where we went out and sampled moths at night all over these different counties. And I think almost surprisingly to us at first, we found an increase in diversity of moths at sites with a lot of streetlights and direct streetlights, and then a decrease at the sites with skyglow.

Then we started reading the ecological trap literature, the literature about animals that have adapted with cues in their environment to do a certain behavior.

And then now with human impacts, that cue is no longer adaptive. It’s maladaptive. And we can’t say for sure whether or not street lighting is a ecological trap for insects, but the way I think about it is that these streetlights are attractive to moths. So they are drawing them into these patches, almost like a sink with the water draining in.

Sarah Beck: So you conclude that artificial light at night can significantly alter composition of an entire taxonomic community of nocturnal moths, or Lepidoptera.

So what is the significance of this? Are there some long-term implications for the health of the urban ecosystem that can be implied as you’re unraveling your understanding of this?

Shannon Murphy: So a lot of our light pollution research that we have is looking at how individual species respond to light.

I think there’s still a lot of species that have never been studied or investigated, and we really need to know how these species do respond to lights.

But even if we know how one species responds to light, or one population’s responding to light, we also have to think about how those species are interacting with all of the other species. And then something I think a lot of gardeners are familiar with is the idea of what we call ecosystem function, or how is that ecosystem functioning?

We think of pollinators as a really important thing for our gardens. So how are the pollinators being affected? And then when they’re affected, how does that affect the whole functioning of our garden ecosystem, so to speak?

We need a lot more research on individual species, but we only have an idea of what’s happening to that one species by itself, or a few species. So what was really great about this work is to see how an entire community’s composition is changing because of the lights.

Something we want to look into in the future is, what parts of that community are changing? Are we getting different species that have different importance to the environment or functions in that environment? We haven’t delved into that, but it would be interesting to know what’s happening with the really important pollinator species, or what’s happening with the ones that are agricultural pests as caterpillars?

And so we need to delve more deeply into that.

Sarah Beck: It just seems like there are endless possibilities, especially when you’re talking about all these different sites as well. I mean, you’ve got urban, periurban, suburban, edge of agriculture.

Shannon Murphy: Kylie worked really hard to find sites that differed in size, because we know that a lot of patterns that you see in community composition of species depends on how big that habitat is. She had a lot of sites spread out all over the Denver metro area, so it was logistically really challenging work to do, for sure.

Sarah Beck: She was going out at night as well to check all these?

Shannon Murphy: Yeah. So we had a crew. Two of the other authors on the paper, César Nufio and I, went out, too, and then we had a crew of really amazing undergraduates who helped us out. We would go out and sample these moths and then at a couple sites for a few years, we would collect them every hour so that we would get an estimate of like when species were coming out at night and when the lights were most affecting them.

That was one of the most challenging things about this project was actually just the working at night. So everyone who worked on this project—almost everybody—was a woman or an underrepresented minority. We started to think about how dangerous it was for us personally to be at these sites at night.

We had some kind of scary encounters, both with people, but then also with coyotes.

Sarah Beck: That is such a fascinating element of this. And we talk a lot about the urban-wildland interface. I think living in the West, you especially experience this sense that a lot of the animal life is accustomed to having these spaces when we’re not there, in the dark.

Yeah, you must be really sort of developing these new protocols for this type of work.

Shannon Murphy: The National Science Foundation actually has a new push where every grant that is an ecology grant that’s going to have field work has to have a statement about how you’re going to ensure safety of the researchers involved, and I 100 percent support that.

Sarah Beck: It just brings up such a fascinating component of urban ecology in general, too. This is a world that we’re moving into, and as garden futurists, we’re thinking a lot about the fact that populations of the West are getting much more urban-centered.

Shannon Murphy. That’s why we have streetlights, is to increase our safety, right?

Sarah Beck: Right, right. I really want to ask you also about the work you’ve done on how light pollution can alter plant-insect interactions, because I think this is where it gets really interesting in this food web conversation.

Could you talk about your findings on artificial light from streetlights having an impact on plant toughness? Now, when I read the word toughness, I’m assuming you’re not talking about resilience.

Shannon Murphy: No. So there’s toughness and hardness. And if you think of a coconut, it’s hard to crack into a coconut, but once you crack into it, it actually splits quite easily. So that’s hardness.

But then toughness is if you think about ripping a leaf, it’s tougher to rip the leaf, or you can get it started, but then like, it’s still tough to get through it. So we were measuring toughness as a physical property of the plants.

This is actually also Kylee Grenis’s work. So she did a greenhouse experiment where you grew different plants in the greenhouse and measured a lot of different things about it. But the one that we looked at with caterpillars, we grew this invasive plant—smooth brome (Bromus inermis)—in the greenhouse, and a caterpillar that we found pretty commonly in the field.

And then she fed them plants that were either from under streetlights or not from under streetlights. And then we did what we call a complete factorial design, where we crossed every of all the factors that you could be thinking about in this experiment. So, we have streetlights in our greenhouse and they’re sodium-vapor greenhouse lights up there that are basically just streetlights.

So we were able to have half the greenhouse under streetlights and half of it not under streetlights. And then we were feeding caterpillars either under streetlights or not under streetlights plants that either had been picked from under streetlights or not from under streetlights.

So we had very real situations of caterpillars feeding on plants but not under streetlights and the plant had never seen a streetlight, or we’d have a very real situation where you have caterpillars under a streetlight feeding on a streetlight plant. But then we also had things you would never find in nature, where we’d have a caterpillar under a streetlight but eating plants that had never seen streetlights, or a caterpillar that’s not under streetlights but eating a plant from streetlights.

So those are things you wouldn’t find in nature, but it helps us understand what the factor is that’s affecting insect growth. And what we found, which was really interesting, was that there was a very negative direct effect of being under a streetlight. So the caterpillars that were under streetlights grew more slowly and didn’t gain as much mass.

Then the indirect effect was that the streetlights were negatively affecting the plants, and then that somehow was negatively affecting insect growth. So even the caterpillars not under streetlights but were eating streetlit plants had slower growth and less biomass.

And so then we measured everything we could think of that people say is important for caterpillar growth. So we looked at carbon and nitrogen and how much biomass there was on the plants. And the only thing that came out significantly different between our streetlit and non-streetlit plants in that experiment was toughness.

The plants were tougher under streetlights. So we presumed, then, that the caterpillars were just having a harder time eating it and maybe it was taking them longer to eat that food.

Sarah Beck: Wow. They were like, “this salad is terrible.”

Shannon Murphy: Yes, it’s a terrible salad.

Sarah Beck: That is such an incredible story.

And I love hearing sort of how you reduced all the factors down to figuring that out, too, because obviously you can’t really ask a caterpillar, like, “What is the problem here? Why is this plant not helping you gain weight? You’re not looking so good.”

Shannon Murphy: So we started growing a lot of different plants in a greenhouse, either under streetlights or not, just to see what happened. When we were doing that research, we did find that some of the plants change what we call a carbon to nitrogen ratio, where they ended up having more carbon and less nitrogen. So in some ways that’s making it like junk food, like snack food, like a Cheeto for the caterpillars.

Other plants change their allocation of resources to aboveground biomass from belowground. So we had more plants above ground and fewer roots.

But then what really blew us out of the water was another terrible invasive plant, cheatgrass (Bromus tectorum). It grew like seven times bigger under streetlights aboveground than when it wasn’t under streetlights. And it just went nuts. It just loved streetlights and was growing so big. And that really surprised us because we were like, “Wow, check this plant out. It loves streetlights.” And since it’s a terrible invasive, that’s not a good thing.

Sarah Beck: This could have incredible implications. I’m assuming that there are other plants yet to look at here, but if this were to be a common trait of a lot of invasive plants, this could be a real problem, right?

Shannon Murphy: Yeah. So we didn’t find it with the smooth brome, another invasive plant, it’s also a brome just like the cheatgrass is, but again, this was a greenhouse experiment. So everything was controlled except for the streetlights. But we wondered then, well, is this happening out in the “wild”? So in the alleys of Denver?

I noticed when I was walking my dog, just anecdotally, I started to notice there was cheatgrass everywhere in Denver alleys. I just wondered, “I wonder if this is happening out in the field—or the wild and urban settings—similar to our greenhouse.”

I helped run a science camp with two of my colleagues, Jennifer Hoffman and Robin Tinghitella. We have a science camp that we do for middle school girls every summer. We had these girls help us design an experiment to test whether or not cheatgrass was thriving under streetlights outside as well as in the greenhouse.

So we did this experiment where we walked up and down alleys, and we did poles that had streetlights or poles that didn’t have streetlights because along with the girl campers, we realized that the pole itself might be just cracking into the cement might be something that’s helping the plants to grow in an alley.

We also did intermediate between the poles to see where there were “not as much streetlight,” although you still have a lot of skyglow, but it’s not right under a streetlight. We also measured plants there and we taught the girls how to recognize cheatgrass. We sampled alleys all over Denver, around the University of Denver.

Sarah Beck: Wow, big data project. That’s awesome.

Shannon Murphy: It was great. We had them help us analyze the data and they learned how to do that. And then they were involved in the publication process. So nine of the campers ended up being published authors on the paper, which was really fun. They’re all in middle school.

We found that we were more likely to find cheatgrass under streetlights than not. We were also more likely to find plants in general under streetlights. And then the cheatgrass, I think it was three times more likely to be found under a streetlight than not under a streetlight.

Sarah Beck: Are there any benefits from cheatgrass as far as habitat or food for insects?

Shannon Murphy: Not that I’m aware of.

But what we started to wonder was if we have eradication programs where we’re getting rid of cheatgrass in more natural areas around cities, but we’re not thinking about what’s happening in the cities, this almost could be a colonizing population to recolonize areas where they’ve eradicated it, or tried to. And so I think that’d be really interesting to think about what’s happening with cheatgrass in urban settings, since it is clearly thriving under streetlights and how that might be affecting populations in more natural areas.

Sarah Beck: Oh, it sounds like there’s just so much more to know on this.

I mean, invasive plant issues are huge, just thinking about all of these spaces in cities. We talk a lot about how even just having connectivity between small ecological patches in a city for pollinators or to benefit insects, thinking of those spaces getting filled with something that is in no way beneficial and is becoming super dominant. From a garden perspective, if you are in an urban environment, you probably want to reduce the amount of artificial light on plants that you’re hoping will be attracting those caterpillars, right?

Shannon Murphy: I wonder for garden plants, I haven’t actually studied garden plants and how they react to streetlights, so that would be interesting to know how they’re changing, too.

But there is research showing that plants senesce later if they’re under streetlights. And I’ve sort of anecdotally noticed this in my own yard. I unfortunately live right underneath an alley streetlight and I have noticed that that part of my garden seems to senesce later than the part of my garden that’s around the garage and not near the streetlight, but there is other research showing that plants senesce later, or lose their leaves, or start to die back later if they’re under streetlights.

For the insect community that’s necessary to have your garden plants, it does seem like it’s not good.

Sarah Beck: It just makes me think of all the things they say about children and screen time. Like you’re not supposed to have your phone right before bed. It makes me think of the garden plants, like, “No, don’t stay up late!”

Shannon Murphy: Yeah, that’s true. I hadn’t thought about it that way. That’s a fun analogy. Are they up late reading?

Sarah Beck: You do have some research that looked at native plant traits. Is that right?

Shannon Murphy: When we did the greenhouse experiment where we first discovered how much cheatgrass seems to like streetlights, we also looked at four different native grasses, and they didn’t react the same way as cheatgrass did, so none of them grew significantly bigger under streetlights than not under streetlights, and none of them had significant differences in toughness. I think one of them had an increased carbon to nitrogen ratio, so it did become a little bit less nutritious for insects.

Sarah Beck: It sounds like there’s just so many more potential things, questions to ask yet, in terms of plant species. You’re talking about just really a few things here. You’re talking about a particular invasive grass, right, and then also some native grass.

Shannon Murphy: Yeah, and we even noticed that when we were doing it with the camp. We wished that we had better abilities to identify all the plants that we were seeing under the streetlights, because we started to notice, we’re like, “Well, this one seems like it’s here a lot, too.”

There’s another example, I study a moth species called fall webworm (Hyphantria cunea) from a completely different perspective, we’re looking at the evolution of diet breadth.

We had started to notice that on nights when we forgot to turn the lights off in the lab—they mate during twilight, and they really need that twilight signal in order to mate. So, to maintain our colony, we turn the lights off when we leave during the day, so that they’d get the twilight through the windows, and then the next morning we come in and they’re all mating.

But we noticed that if we forget to turn the lights off, or if our safety light in the lab stays on, that our mating doesn’t seem to happen. So then this summer with the camp again, we started to think, well, maybe we can look at how streetlights might affect moth mating.

So the campers helped us design an experiment again, where we put mating moths, and we keep them in these plastic shoeboxes that we get from Home Depot that are clear plastic. That’s where we put the moths into mate. We put the clear shoe boxes either under the streetlights in the greenhouse or not under the streetlights in the greenhouse.

I thought there’d be a difference and there would be fewer matings under streetlights than not under streetlights. But what we found was that no moths ever mated under streetlights, not one.

So now I’m starting to wonder, especially with the work we found with the community composition changing, is that if we’re drawing moths into these streetlights, but then they’re not necessarily mating under the streetlights or their offspring, the caterpillars, are experiencing negative effects from feeding on plants under streetlights or just being themselves under streetlights, this change in community composition that we’re seeing is probably manifesting through all different parts of the life cycle in the field, and that’s something we haven’t investigated either. So that would also be interesting.

So we’re analyzing those data right now. And one of my current graduate students right now, ​Mykaela Tanino-Springsteen, is writing that up as a paper, so that’ll be exciting because now the campers from this year will be on that paper, too.

Sarah Beck: The impacts of artificial light have been explored for few invertebrate systems and not at all for plant communities that are surrounded by urban areas.

As we have emerging scientists coming into this field, and as you mentioned, this is really a new frontier, can you speak a little bit about just where you think this field needs to go?

Shannon Murphy: So I think there’s lots of things that would still be extremely valuable for us to know.

I talked earlier about how there’s a lot of studies looking at how one insect or maybe one plant is affected by light pollution. And I think that’s still really valuable, though, because there’s so much we don’t know about how other species are interacting with light. So I’ll continue doing that research, too.

But I will also say that I think where we need to be headed is to be looking at what I call a community perspective.

So in ecology, we think about populations of the same species, but then when we have all the species that are living in an area interacting there, that’s called a community. And we really know very little about how communities are responding to artificial light at night. And so it’s really important to know not just how individual species are responding, but then as we know how those species are responding, how is that affecting all of the interactions within a community?

So are we losing pollinator species? Which functional groups are being most affected? Is it the predator insects? Is it the decomposer insects? Is it the herbivorous insects or is it the pollinators? And then how are those individual species changes affecting the rest of the community?

And that I think is wide open. There are very few papers that look at entire communities of organisms and how they’re responding to light pollution.

And indeed, the paper that just came out last week was in a special issue of the Proceedings of the Royal Society. That was the theme of the issue, is that we need more community work and there’s other community papers in that issue, which are great, but that seems to be something that many of us are thinking is that it’s also time to move past individual species interactions and be thinking about community-wide impacts and how that’s affecting the function of our ecosystems.

Sarah Beck: You mentioned a couple of times, just the individual gardener experience. I’m really curious how this field might be able to impact broader urban planning. I mean, could you imagine a day in which recommendations might actually be given?

Shannon Murphy: Some urban areas are already doing that. So for instance, one of them that I’m the most familiar with is Boulder, Colorado, which is near here in Denver. They actually made a mandate that everybody needed to swap out their porch lights for lights that shine only down.

So some communities of humans are already doing this and figuring out—and I know there’s other instances too, where some cities have made rules about how bright the streetlights can be and where they’re shining and whether you need to cap them so that they only shine down.

So you still have the safety component of the light, but that it’s maybe not going to be affecting organisms that are flying above the lights as much.

There’s somebody I was talking to who studies this, but from Germany, but they always look at the satellite images. It’s Experimenting with Tucson Night Lights, and Christopher Kyba is the person who did it. They brightened then dimmed some streetlights for a few nights using satellite images to observe changes in Tucson’s radiance. I remember hearing about it thinking, “Wow, that’s really cool,” because they got a whole city to do like an experimental design where we’re going to dim these streetlights.

Sarah Beck: There’s so much opportunity, it sounds like, for citizens to be advocates and for people who live in cities to be paying attention to this issue.

Shannon Murphy: And I think it is something that we as citizens can be intimately part of.

So I know I personally keep my porch light off as much as I can and don’t leave my lights on outside and try not to light up the night sky as much as possible. But tempering that with the understanding that we do need streetlights in order to be safe in an urban area, and I totally understand that. We don’t want students walking home at night in dark alleys.

How do we maintain our own safety, but without impacting the ecosystem as much as possible?

Sarah Beck: It sounds like, to keep it simple here, if you’re a gardener, lighting that goes down and not up is probably a great place to start and is simple, and as you mentioned, turn off the porch light or turn off the unneeded outdoor lights, right?

Shannon Murphy: Yeah, if you can install lighting at your house that isn’t on all night and shines down, that’s the best we can do right now, I think.

I personally don’t have extraneous lighting out in my garden that I don’t need. I don’t have any lights in the back and then I have my porch light off all the time just to try and be a friend to a friend to the moths.

Sarah Beck: And embrace the darkness, right? Go out and experience the beauty of the night and that darkness experience.

Shannon Murphy: Yeah, and it’s fun that that has become a theme for the camp that we run every summer, because there’s two of us who are ecologists who run it. And then the third person’s an astronomer—

Sarah Beck: Oh, wow!

Shannon Murphy: And they clearly have interest in light pollution too, but for different reasons, because we can’t see the stars at night anymore.

And so all three of us realized that even though we bridge fields from biology to physics, we’re all three very interested in artificial light at night and how it’s negatively impacting our areas of science. So it also is bridging different scientific areas, which is really exciting, too.

Read Next: The Night Garden

By: Katherine Renz

As we fall our clocks back an hour in November and the night creeps ever longer through December’s winter solstice, gardeners are presented with an opportunity to connect to the dark. After a nine-to-five workday and sundry obligations, it is often evening or later by the time one can make it into the garden. Introverts may thrive in the peace and stillness that descends once most of their loud fellow humans head indoors. In our relentlessly optimistic culture, it can be a relief for some of us to get in touch with our dark side, appreciating the free, subtle gifts of the twilight.

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Sarah Beck: This is an area of research that is pretty recent in its importance, because the globe was so covered with bright light up until fairly recently in human history. And now we have this burgeoning field of study around light pollution and impacts of artificial light at night.

Katherine Renz: Thinking about how many insect species there are and then how many plant species and how many relationships in that web, the permutations of that. Then doing that research and then using that research to actually take concrete civic or political action to start changing this urban infrastructure. And just on our own scale, how we garden and what we can do as gardeners?

Sarah Beck: Let’s talk about that. Just how much artificial light is impacting our ecology is really incredible. It’s such a human problem, or rather a human-created problem. And this is also what makes this research feel hopeful, I think, in the sense that, as we’re becoming more urban, as humans are living in cities even more, we have this opportunity to take action and to do something about this.

Katherine Renz: It’s surmountable. It’s not like some of these other grand problems that are also from the last hundred years and human induced.

I mean, you look at Flagstaff, a city where over 20 years ago, in 2001, they were designated a Dark Sky City. And you look at the work that’s been done in Tucson in the same way and experiments that they’ve been doing. And simple solutions like directing light downward rather than up into the sky or turning off the lights at night.

It is hopeful. It’s exciting to see that there are models happening in cities more and more each day, I think, and it feels concrete and relatively simple.

Sarah Beck: I think this is a fascinating conversation about city design and planning as well. I love when we get into things like this, because when we think about change we can make in a microcosm such as our own garden, that’s really cool, this idea of downlighting and really thinking about what light needs to be there. But then we think about just that large-scale sense of design and could we be designing our cities in a way that creates space for all of the other ecological processes that need to happen?

If a park was set up, obviously for humans, for people to walk through and feel safe in the dark, but also, wow, is there a place for the moths to mate?

Katherine Renz: We just need more ecologists and entomologists in the city planning and board of supervisors.

Sarah Beck: I think this is a fascinating space we’re getting into with just the urbanness of life. Actually, the urban conversation with Dr. Murphy I thought was very interesting. I feel like she was saying that the fact that all of these plants that she was studying were not in a wild nature environment. They were in an urban setting like an alley.

Katherine Renz: I mean it’s sort of that other side of the nature connection coin, right? Of how even if you live in an urban environment, you can still get connected to nature, and the nature in an urban setting is still getting affected by things and how so and how do we manage that?

Yeah. New campaign: Design for Bugs. I love the moth mating garden.


Murphy Lab

DU SciTech Summer Camp

This conversation references several initiatives for light pollution mitigation. Flagstaff, Arizona, became the first International Dark Sky City in 2001. Boulder, Colorado, adopted an outdoor lighting ordinance in 2003. Christopher Kyba led a citywide streetlight experiment in Tucson, Arizona, summarized in the 2021 NASA Earth Observatory article, “Experimenting with Tucson Night Lights.

Grenis, Kylee, César Nufio, Gina M. Wimp, and Shannon M. Murphy. 2023. “Does artificial light at night alter moth community composition?Philosophical Transactions of the Royal Society B 378 (1892).

Murphy, S.M., D. K. Vyas, J. L. Hoffman, C. S. Jenck, B. A. Washburn, K. E. Hunnicutt, A. Davidson, et al. 2021. “Streetlights positively affect the presence of an invasive grass species.” Ecology and Evolution 11 (15).




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