Native vs. Non-Native: Examining the Effects of Pollinator-Friendly Plantings (Ep. 26)

With climate change impacting biodiversity and insect populations, including bees, finding solutions for their conservation is critical. Loss of habitat is a big bee stressor and we can support bees by making sure they have the floral resources they need. But should we plant only native flowers, or can some pretty non-native flowers get the work done too?

Today, we’re talking with Dr. Nicola Seitz about an experiment she conducted comparing the bee community composition between plots seeded with native and non-native pollinator-friendly plants. There were a lot of interesting findings and learnings here. For example, the non-native plots attracted more bee species overall, but some bees were exclusive to native plants, emphasizing the importance of both types in supporting bee populations. We also discuss the need to adapt to changing environmental conditions while prioritizing the preservation of intact natural systems whenever possible to effectively support bee populations. Get all the information she learned conducting her garden experiment here.

Good to know

Visitation networks are how foragers, like bees, distribute themselves within and among resource patches, like flowers. Different factors are at play as to how and where bees go to get their nectar and pollen. Flower patches with high levels of nectar, the distance between resources, the bees’ knowledge and experience of the environment and their interactions with other bees and potential predators all influence the decisions they make.

Transcript

[00:00:00] Welcome to The Bee’s Knees. I’m your host, Jacy Meyer. The Bee’s Knees is a podcast wild about native bees. Wild and native bees are under threat worldwide. In each episode, we look at actionable things we can do to support these adorable little guys whose pollination work is crucial for maintaining biodiversity. Thanks for being here.

When you’re thinking about your garden and yard, what to plant is a huge consideration. Suitability for your local environment. Garden size and the commitment and care different plants require will all factor into your decision. If you want to make sure you have a buzzing garden that attracts and keeps bees and other pollinators, you may also be considering planting native flowers.

Experts typically recommend planting native plants for pollinators, but are [00:01:00] non native plants bad for bees or just not as beneficial as native ones? Today, we’re going to dig into the research with Dr. Nicola Seitz, who published a study which strives to answer if native and non native pollinator friendly plants are equally valuable for native wild bee communities.

Thank you, Nicola, for joining us. I’m really interested to know what led you to look into native and non native plants and their comparable value to bees. Yes. Thank you for inviting me. Of course, we live right now in a world of change with climate change happening. We’re facing biodiversity loss, and we’ve also seen a strong insect decline and specifically bee decline over the past years.
So of course, that means that we need to find solutions for the conservation of the bees. I mean, a lot depends on the bees, so it’s very important. Obviously, our well being depends on [00:02:00] it, and in an effort to conserve bees. What we’ve also seen that many pollinator friendly plant mixes are being compiled, promoted and sold also.

However, very often these mixes contain both native and non native plants. And it was a bit unclear what that exactly meant for the bees or also the bee communities. And not a lot of research had been done in that regard, and that’s why I was interested in it. I mean, like I said, and I think it’s a very pressing question for us to find solutions for bee conservation.

Can you describe the garden experiment you conducted? Yes, of course. So I conducted my common garden experiment on farmland of the University of Maryland in the U. S. And there, I worked at three different sites. And at each site, I always had two [00:03:00] plots. uh, next to each other. One plot was seeded with a mix of native pollinator friendly plants, and then the other plot was with a mix of non native pollinator friendly plants.

And each plant mix contained 20 different species, and I tried to find a good mix of really very different species, so I tried to include flowers that would overall cover the entire potential flowering season. So spring to fall, I try to include flowers, plants with different flower colors, for example, or also plants of different plant families.

So to really have like diversity in those mixes. And then once I established these plots and these sites, I then Sampled the bees at those plots and recorded the visitation also to the specific plants. And I did that over the course of two years. Yeah, so that was [00:04:00] my basic setup for my experiment. Okay, so now I’m going to ask you specific questions about what you found because this is very, very interesting.

First, what were the main differences in the overall bee community composition between your native plant plot and your non native plant plot? Right, yeah, that’s a very good question. I mean, overall, we found a slightly lower number of bee species in our native plant plots compared to our non native plant plots.

So this was, in numbers, this was like 49 species on native plants versus 63 bee species on non native plants. However, at the same time, Although this number was a little lower on native plants, we still had, at the same time, bees that were only occurring, for example, in the native plant plot. So that was 11 species that we found only on the native plants.

And then on the non native plants, [00:05:00] there was, for example, 23 species that only occurred on the non native plants. But then additionally, We also found bees that would visit both plant types. However, they had a stronger preference for one plant type, let’s say. So, these would be generalist bees that visit a lot of different flowers, but they would more often choose one plant type over the other, one plant type plot, let’s say.

So, this was the case, for example, for One of the bumblebees that we recorded, which was Bombus bimaculatus, and this bumblebee was visiting both plant types. However, we found it a lot more often on our non native plants. And then the large carpenter bee, on the other hand, Xylocopa virginica was an example that also visited both plant types, however, was visiting the native plants a lot more often.[00:06:00]

So what did you think about that when you saw that? Generally are in the category of pollinator friendly or categorized like that. So all of these are supposedly attracting lots of bees and providing lots of nectar good resources for the bees. And of course, when we select only native bees, we have a lot.

Native plants, of course, we have a lot less variety to choose from. It’s much more restricted than available plants, let’s say. Now, if we go for the non native plants, we can really go for the ones that are known to produce lots and lots of nectar that are easy to grow also. So, in that sense, it kind of makes sense.

However, of course, there’s more details to this. In the end, it’s not just the number of bee species. Like I said, there’s different preferences. And then maybe one particular point that I would also like to point out here that deserves particular attention is the case of the so called specialist bees. [00:07:00] So these bees, also called oligolectic bees, they feed on very Specific pollen, and they need that pollen from very specific plants to feed and to survive.

And, of course, with specialist bees, everything becomes a bit more tricky. And in our study, we did not encounter a whole lot of oligolectic bees, but a few. And one example was, for example, the mason bee, Osmia distincta. So this bee is specialized on penstemon flowers. Penstemon, that’s a beard tongue plant.

And we did have penstemon also in our native plant mix. So this was a very specialized interaction that we observed. And we did not observe any specialized interaction of this. kind of like a really of an oligolectic bee with the specific plant that they need, non native plants, which of course also makes sense kind of that, uh, the local native bees are specialized [00:08:00] on the local native plants.

When you were talking about your experiment, you said you were quite conscious about planting flowers that would bloom through the entire season, right? So you had your early bloomers in the spring all the way through until the fall. Did the visitation networks differ between the early and the late seasons?

Yeah, good point. Maybe I should also add as an information that one thing that also happened, I mean, I seeded everything at the same time, um, nonetheless, the onset of flowering was, for example, a little bit different and the native plants actually started flowering a little later than the non native plants.

Nonetheless, we had those higher numbers. Of course, it makes sense when we don’t have flowers in our native plant plots, that we don’t have, uh, bee species. Yes, of course, that makes sense. But even taking that into account and looking only at the sampling dates for both kind for flowering. still had those higher numbers of bee species on our non native plots.

Not always, sometimes they were also similar, but sometimes they were higher [00:09:00] on our non native plant plots. And then, yes, you were mentioning something very important, the actual visitation networks that we also analyzed. And first of all, I would like to mention in that regard that also the visitation networks actually differed by plant type.

So, I mean, yes, you were already asking about the season and that’s another point. But first of all, just by the plant type, our visitation networks already differed. So overall, the networks of our native plants with our bee species were more specialized than our networks of our non native plants with bees.

So that was the first finding related to the networks. And then the second finding was that we also observed a seasonal difference. Exactly. So in this case, our early season, so spring networks between bees and plants, and this was across all plant types. were actually also more specialized than our late [00:10:00] season fall network.

So the specialization of the networks kind of decreased over time, over the course of the year. And also, just to explain a little better what I mean by specialization of the network, that basically means network is more specialized when. A bee tends to visit just specific plants and not all of the plants.
And the more often we have this case, that bees visit specific plant types, the more specialized the whole network is. So was there anything that surprised you in the findings? The seasonal difference, um, Yeah, that was something that I hadn’t anticipated that much, let’s say, so that was very interesting.

And I also have to say that there are not that many studies that span this entire flowering period from spring to fall, really, or that even differentiate between the seasons. So a lot of other studies that we see are focused on [00:11:00] summer as the time period with most bee activity, probably. And my study here shows a little bit, our study shows that there is, there can be differences in the season and this is maybe something we should pay more attention to and that we should maybe look into more in future studies.

So maybe I would like to add here because maybe now people are confused. Okay, what does that mean? So should I use non native pollinator friendly plants or not? And I think what the study shows is that non native plants, they can, in some cases, for example, buffer some flowering gaps. So for periods where native plants simply are very scarce, we can add additionally some non native plants in order to provide some food for the bees. I mean, of course, in general, native plants are always kind of the best option if they are available. So I wouldn’t shift from native to non [00:12:00] native plants. It’s really more like an complimentary thing. And additionally, I would always, when we use non native plants, we need to be really, really careful.

So I don’t want to promote that too much here. And in the cases that we do use them. Only be in landscapes that are already like, let’s say, heavily human dominated, where we already do not have natural landscapes anymore, because I mean, the first choice is always an intact natural system, and we do not want to bring any non native pollinator friendly plants in there.

Now, as I said, we’re living in a world of change with lots of land use changes, climate change happening. And we just need to deal with these different circumstances that we have now. So we often do not have that option of the completely intact natural system anymore. And for example, where we would have a natural meadow and then adjacent to the meadow, we have the forest.
And so the bees feed more in the forest in the spring, and then they move over to the meadow in the [00:13:00] summer. So we don’t have this ideal situation in a lot of cases. So that’s why we need to come up with solutions. And that’s why we have the pollinator friendly. Plantings in the first place that we add to our landscapes where it’s useful.

So why did you choose to work with bees? Well, I think bees are really, really cool creatures. They’re really fun to watch. They have so many different colors and they can be really, really furry and big, or they are really sleek and tiny. They have. Really interesting behavior also. I mean, some bees are social, others live solitary, some are even faculty of social.So I think they’re really an amazing group of species. So yeah.

It’s complicated, isn’t it? It seems like a given to go with native flowers for our native bees, but high quality pollinator friendly non native flowers do have a place in our gardens. I’m very grateful to Nicola for [00:14:00] breaking it down for us.

And of course, I’m grateful to you, fellow bee fans. Thanks so much for joining me, and do visit the beesknees. website to dig a bit deeper into the native versus non native plant discussion. Until next time, remember, flowers for all seasons.