How Forests Support Bees (Ep. 9)

One of the greatest threats to bees is the loss of land. Open meadows and grasslands are disappearing, being swallowed up for agriculture or turned into developments. One natural landscape that isn’t gobbled up as quickly is forests. And it turns out forests have a lot to offer bees.

Forests play a crucial role in bumblebee biology, particularly during early spring when understory spring ephemerals bloom before the canopy emerges. This concentration of resources provides an essential food source for bumblebees. Additionally, forests serve as potential sites for overwintering and nesting, making them even more vital for the survival of bumblebees. Understanding the importance of forests in supporting bumblebee populations can help us better protect these important pollinators.

Many thanks to Dr. John Mola from Colorado State University. Learn more about his research into the importance of forests to bumblebee conservation. John mentioned another researcher looking into wild bees and forests. This webinar is a deep dive into how bees use a forest’s resources.

Did you know?

The rusty-patched bumblebee (Bombus affinis) has been listed as federally endangered in the US since 2017. We could say John was cautiously optimistic about what he and his colleague were finding on their cross-country bee-hunting road trip. But the numbers are still out. 

The rusty patched bumblebee is a social species. Its annual cycle starts in early spring when colonies are launched by solitary queens emerging from overwintering sites. The process continues with the production of workers throughout the summer and ends with the production of males and new queens in late summer and early fall. Reasons for their decline include an introduced pathogen and exposure to pesticides, but also habitat loss, non-native and managed bees, and the effects of climate change.

Transcript

[00:00:00] When we think about planting for bees, fields of flowers and gardens planted with a variety of floral shrubs and other nectar rich plants spring to mind. But these aren’t the only habitats that contain rich food and potential nesting places for bees. Forests are full of good stuff for pollinators and may be a bit more immune to the challenges that other habitats face.

Let’s take a wooded walk with Dr. John Mola. He’s an assistant professor at the Department of Forest and Rangeland Stewardship at Colorado State University in the US. Thanks for being here John. Before we go deeper into the forest, so to speak, I want to start with a seemingly obvious, but actually very important question.

How do you define forest? Yeah, that is a good question. So, [00:01:00] you know, I remember preparing for a forest ecology class not too long ago, and, I forget the exact number, but there’s something like 700 different definitions of forest. I might be getting that off by an order of magnitude, but quite a large number of different definitions of forest.

But typically it’s an ecosystem that is dominated by the presence of tree form vegetation. So that’s kind of vague and jargony, but it’s a landscape where some portion of the overstory contains and is, you know, the ecosystem processes are sort of defined by the presence of those trees. So some definitions kinda suggest about 30% canopy cover or more others would call that a woodland.

But for the purposes of how I think about it with kind of bees and bumblebees, specifically, landscapes where trees are important to bee biology and ecology. So why did you become interested in looking at the role for play in supporting bumblebees? [00:02:00] Yeah, that sort of arose both from working with this species called the Rusty Patched Bumblebee, which is the first federally listed bumblebee species in the United States.

And so it’s kind of like this lightning rod of bee, and specifically bumblebee conservation in North America. And as we were doing field work with the species, we were doing a population genetic study. And kind of traveling around the Midwest collecting genetic samples from this bee, and we really felt like in the literature, in natural history writings and things like that, the species is kinda described as a generalist.

Um, but we, we were going to so many sites looking for this one particular bee, that eventually it started to feel like, well, there’s no, there’s no woods around, there’s no, uh, forest around this site, I really feel like we’re not gonna find this bee here. Uh, and then we go to another site where we felt like, oh, okay, we’re in this meadow.

[00:03:00] You know, we’re collecting from these plants that are blooming in an open habitat in the middle of summer. But I can see that forest, you know, that we’re right next to, or I see a nice riparian area a couple hundred meters away. I really feel like we’re gonna find Rusty Patched Bumblebee here and then we would, and you know, it wasn’t perfect and that’s anecdotal or whatever.

But then started kind of long drives of hours between sites and going across the Midwest. Me and my colleague and co-author Ian Pearse were just kind chatting in the car like, oh, it really seems like these forests are super important. We did some other analyses that sort of suggested that floral resources were declining in Midwestern forests.

And those floral resources were particularly important for queen bumblebees. And so kind of like those two things. Plus, you know, talking and realizing like, oh yeah, there sure seems like there’s a lot of papers where the amount of forest [00:04:00] in the surrounding landscape seems to matter, but the studies are actually done in meadows or open habitats in the middle of summer.

And so, you know, are we overlooking that importance of forests and our studies kind of collectively as a research field, are we coming to the same conclusion that forests typically are important, but we’re never directly studying them or, or rarely directly studying those forests. So just that sort of observational and, and discussion kinda led to

you know, it would be cool to explicitly study forests rather than just have it be this kind of conclusion that we come to while looking at other things. Can you share a little bit about what forests provide bees and why timing is so crucial when we think about the different needs bees have throughout their lifespans?

Yeah, so I’d start by saying that I have my own bias, and then there’s kind of a [00:05:00] bias in the literature. Which is often when we’re talking about forests in this context, we’re often thinking about temperate, deciduous forests, and so in that case, the timing of in the year, in the season when forests are particularly important to bees is really stark.

So I’ll give an answer about that in a second, but I just want to point out that, you know, in, in some other forest systems like mixed coniferous forests, for example, if those forests are healthy, if the density of trees is kind of within the historic range of variation, then oftentimes they might have floral resources that are available in the understory, kind of continuously

throughout the season and not have this really pronounced spring effect. But most of the research, most of our understanding and possibly, you know, that reflects the relative importance comes from these kind of temperate deciduous forest. Whether that’s, and a lot of those studies have been in, been done in, in [00:06:00] Japan, in the eastern United States, and a little bit in Europe as well.

And yeah, and in that case, again, especially for bumblebees, because they kind of have these long flight seasons where they grow through these annual colonies early in the year. These forests may have a particularly outsized kind of importance in bumblebee biology because understory spring ephemerals can have these blooms early in the year before the canopy leaps out, and so that provides a really concentrated set of resources, especially when those forests are healthy.

We can come back to what forest health means in a minute uh, but you know, there’s also overstory resources. So black cherry, red bud, things that are maybe typically more thought of as flowering trees. But also things like maple, which are typically described as wind pollinated, but bees will also forage on them.

There’s that big importance of floral resources in the [00:07:00] understory and overstory, and there’s some great work by Kass Urban-Mead for her dissertation. She actually kinda hoisted herself up into the canopy of trees to do observations and collections of bees, and so it has some really great work. And then there’s also the potential importance of forest as, uh, sites of overwintering and nesting.

And this tends to be a little bit harder to study, but we have various observations, including some of our own, where we find bees, overwintering, preferentially in forests compared to other habitat types, but also indirect measures like from genetic mark recapture studies, finding things like higher abundances of,

higher estimates of colony abundance when there’s higher proportion of forest in the landscape. So yeah, forest can be really important for bees in a variety of ways, and in some agricultural systems, probably in [00:08:00] some wildland systems as well. These forests can be, it’s especially important kind of indirectly modulated through bees by increasing pollination services or, uh, increasing the presence of beneficial insects like bees, but also parasitoid wasps.

And sometimes that happens through abiotic means where these forests set up wind breaks for the crop that make a more favorable environment for flights and therefore for pollination. So sometimes it’s these direct effects on bees and sometimes it’s these effects on pollination indirectly through the bees.

So can you say if there’s a certain type of forest that is more beneficial to bees, or does it really, a lot of it depend on how healthy the forest is. I wouldn’t say that there’s like one forest type that is best for bees, because you know, bees, as y’all are aware, have this, you know, that’s a big group, right? There’s over 20,000 species with a lot of [00:09:00] variety and diversity there.

So that’s one thing me and some collaborators have been kinda toying around with is like, I’m interested in bees and bees and forests and now situated within kind of the center of North America. And then we have collaborators on the East coast, collaborators on the West coast. And surely collaborators internationally as well.

But you know, as we kinda started, like a forest isn’t, a forest isn’t a forest. There are all these different things. Some forest types, their historic state is incredibly dense with basically no understory flowering resources, and that is healthy in those forests. In other forest types, they have become very dense.

Outside of the historic range of variation, and certainly outside of our desired range of variation. And so we would consider those forests unhealthy. So yeah, this idea of forest health is very subjective. So yeah, I think that that’s also been kind of an interesting part of this kind of [00:10:00] journey of merging bees and forest ecologies, that we get trained as entomologists or we get trained as forest ecologists,

and so now I’m kinda trained as an insect ecologist and kind of learning more and more about forest ecology. And that’s really kinda shaping how I think about these issues. I don’t know if that answers the question, but, uh, that’s where my mind went. No, that’s great. That’s great. That brings me perfectly to my next question.

So are there any landscape and forest management practices that we should encourage or on the other hand be wary about? Yeah, so this is one of those areas where I think there’s really kind of a win-win opportunity. You know, my knowledge is very North American biased, but largely if we’re talking about deciduous forest or we’re talking about evergreen forest, that’s gonna translate to whichever specific tree species we might be talking about across continents.

But here in the Western United States, for example, one of the big issues is our forests are outside of this [00:11:00] historic range of variation in terms of stand density. So because of these really dense forests with a lot of what are called ladder fuels, which are basically understory trees that are either alive or dead, that can cause fires that would kinda controllably or in a desired manner in the understory, it can cause those fuels, can cause that fire to ladder up into the canopy and then get these really high severity uncontrollable fires.

There’s some forest types where those high severity fires are kinda the natural state of fire in those systems. But there’s a lot of forest types, especially the ones that might be particularly important to bees in this region where that is not the historic state of fires. So typically fires in those systems would burn as surface fires.

And the large mature trees would survive those fires. So there’s a lot of effort, including led, much of it led by folks in my department, uh, to thin forests, remove those ladder fuels [00:12:00] and enact prescribed or controlled burns onto those landscapes. Those things are done primarily for fuels management, but the win-win here is that those same things tend to have positive effects on bees kind of across the board.

You know, assuredly there’s winners and losers, but there’s more winners than losers in the bee community when that kind of thinning occurs. And there’s some work showing that those high severity fires are actually quite beneficial to bees so, this fire management and the reintroduction of fire on the landscape, um, you know, is desirable for forest health and management kind of broadly.

But it has these positive effects on bees as well. We can pull other examples in the East where there’s some issues with invasive sub canopy species of plants. Their removal and management can often be, uh, also have these positive knock on effects for bees as well as other animals of particular [00:13:00] interests.

There’s kind of a cool example with the red woodpecker. Where the same management practices that are done in southeastern pine forests for that species also have positive effects on bees as well as butterflies. You know, I think this kind of forest health and management, these same things that we might do for fuels treatment or we might do for these large charismatic megafauna,

they tend to have these positive effects on these insects of interest as well, which, you know, perhaps is not surprising because if that’s the historic kinda state of those forests, then those are the characteristics and stand structure that all of those organisms sort of evolved and are adapted to.

What’s your favorite bee? I always say a Frisbee. Oh, good one. Yeah. I dunno if the camera will pick that, but let’s see. Oh yeah, I have a few on the wall over there. Are you a professional? No, but, [00:14:00] uh, couple of those, well, two of them have a Rusty Patched Bumblebee artwork on them, and the other has a Franklins Bumblebee artwork on it.

So, blend the two whenever possible. That’s true. Okay, so then what is your second favorite bumblebee? Or is it even a bumblebee? Doesn’t have to be a bumblebee. Okay. If I have to choose a, a favorite actual, bee species, entomological bee, yes. My heart probably does belong to the Rusty Patched Bumblebee right now.

Just spending so much time kinda getting to know one species and. Yeah, so I, I’d say Rusty Patched, but I really, you know, can’t decide. Since you have spent so much time studying that bee and I know it is quite endangered, what have you learned? Is it thriving in areas? Is it making a comeback? How’s it doing?

Yeah, so, uh, the Rusty Patched Bumblebee seems to be, you know, it’s kinda interesting, I’m trying to wrap my head around this right now because, that same [00:15:00] genetic study that we were driving around collecting specimens for we’re, now we have that data and we’re now analyzing it, and what we’re finding is that colony abundance for the species is really low and much lower than we might expect. Right now

I’m analyzing that same data that I mentioned collecting before, where we traveled across the Midwest and got a bunch of genetic samples. We also had collaborators send us genetic samples from the Midwest as well as one population in the Appalachians. What I’m trying to wrap my head around right now is that there’s these sites and areas in the Midwest as well as the Appalachians.

Where it seems like we can go year to year and very reliably find Rusty Patched Bumblebee. At the same time, when we look at the genetic data, you know, there’s not a lot of evidence of not super strong evidence of, you know, a lack of genetic diversity or something like that. But [00:16:00] basically, when you have this genetic data from bumblebees, you can ask, well, I caught one individual over here and I caught another individual over here.

Are these two siblings, and you can do that with dozens of samples, and that allows you to say, okay, we caught 20 individuals, but how many colonies do those individuals come from? We don’t know where the colonies are located in the landscape, but we know, okay, we caught 20 individuals and they’re from 15 unique colonies.

So a few of them in the data set are siblings of each other. Typically when you do that with a common species, what you find is that I caught 20 individuals and 20 is not a very big sample size. So we detected 20 unique colonies, meaning every single individual in the dataset is not a sibling of each other, or maybe we get two siblings and so we detected [00:17:00] 19 colonies or something like that.

What we’re finding with the Rusty Patched Bumblebee data is, when we collect 20 individuals, they’re coming from something like eight or nine colonies. So even at these sites where we’re seeing lots of individuals year to year, and we can kind of reliably observe them, we’re finding that there’s not a huge number of colonies there.

And I should say this is still all preliminary and we’re kind of working through it, and there’s some issues of spatial scale and there’s some nuance to it. But right now, it kind of seems like, well, those populations are consistent, but we don’t have a good sense of, well, are they slowly declining over time?

Or are they holding steady or are they even increasing? So right now, I would say that’s kind of the active question, you know, is are these populations of Rusty Patched Bumblebee in the upper Midwest that we sort of view as the stronghold for the species, are they [00:18:00] truly doing well? Or are they slowly declining and they just didn’t decline as rapidly as the populations in the East did.

What do you believe is the biggest threat to bees and what can we do to help? The way you phrase that, for some reason makes me want to say education and misinformation. I think the other big threats are loss of habitat, loss of floral resources, pesticides, and competition with non-native or introduced species.

And of course climate change, which I often forget to list because to me it just seems like the background of everything. So, but for some reason, the way you phrased that question made me think of education and misinformation, and I think we live in a strange world, maybe we always have, but if I do a Google search right now for bees, you know, the first thing that comes up for me are like interesting facts, National Wildlife [00:19:00] Federation, et cetera.

If I open a private window that doesn’t have my user history in it, and I type in bees, you start to get like how to get rid of bees from my attic, pests world for kids, and you start to get these things that show these much more kinda negative perceptions of bees. And so you sort of have that where I think a lot of us are very sold on the idea that bees are interesting creatures in need of conservation, but that’s not a necessarily a broadly held view.

Maybe it’s growing and much better than say for how people perceive wasps, which are also these critically important organisms, and most people reduce them to a couple nuisance species compared to the hundreds of thousands of beneficial species. But the other issue, especially in North America and in other parts of the world where the European honeybee is not native.

Is this sort of misplaced good [00:20:00] intentions, which is this idea that, you know, we can save the bees by becoming beekeepers ourselves and as listeners, and you are likely aware, at least in North America, and again, other parts of the world that are not Northern Africa and Southern Europe, honeybees are not native to these areas.

And we keep ’em in these boxes with tens of thousands of individuals. And so they can certainly outcompete other species, but they can also spread disease to those species. Is that particular issue the biggest threat? No, I don’t think so. But is kinda a, just a lack or a concern for the natural world,

bees being part of that an issue and, and I certainly think so. For some reason the phrasing of your question made me go with this kind of education and cultural perspective rather than the typical things of pesticide and floral resources, but I think that’s all kinda wrapped into that same issue. Have you found any good sources or [00:21:00] ways of kind of fighting against this misinformation?

Yeah, I’m not sure that I would say good other than just, you know, you just gotta keep doing it. And I have that kind of perception or perspective. But at the same time, you know, in Colorado where I am, our governor is quite interested in policies that are favorable to pollinators. So at the same time, we’re beginning a new project that is geared at providing policy recommendations and applying what we know scientifically to things that are legislatively possible.

So, but there are also lots of folks that are more and more interested in pollinator gardens. I mean, there’s this podcast, for example, and things like it that sort of suggests a greater awareness. At the same time, bees, yeah, you can search and some of the results will be pests oriented, but they’re also incredibly popular organisms used in tons of artwork.

And so I think there is a change [00:22:00] in that as well. Just perhaps not where we ultimately would like it to go.

I learned a lot about forests there. Did you? Healthy forests don’t just impact the trees and other flora living in them, but all the species that rely on its resources. And we got a bonus update at how the endangered Rusty Patched Bumblebee is doing in the US. Be sure to go to the website, that’s the bees knees.website and check out the show notes.

We’ve got a link to John’s research plus a video featuring Cass Urban Mead talking about wild bees and forests, and of course, some images of John’s second favorite bee, the Rusty Patched. John also said that he’s worried about the lack of information and sometimes misinformation out there about bees and other pollinators.

So for the love of bees, share some good bee news. A great start would be sharing this podcast. We thank you for telling your friends, leaving a review, and signing up for our newsletter. Thanks again for listening. Do get in [00:23:00] touch with your good bee news. And do join us again in two weeks for the next episode of The Bee’s Knees.