Pollinator Confidential
The Arbornet
Just in time for Arbor Day, Lisa and Pam are joined by Penn State Extension educator Cathryn Pugh, who guides us through the underground maze of mycorrhizal networks, revealing how trees and other plants share resources and communicate distress. Before you plant that free sapling, tune in to learn the untold stories of tree communication!
Just in time for Arbor Day, Lisa and Pam are joined by Penn State Extension educator Cathryn Pugh, who guides us through the underground maze of mycorrhizal networks, revealing how trees and other plants share resources and communicate distress. Before you plant that free sapling, tune in to learn the untold stories of tree communication!
Hello everyone and welcome to Pollinator Confidential, a podcast featuring the untold stories of native plants and the pollinators who love them.
Pam:I'm Lisa Schneider and I'm Pam Ford and we are Penn State Extension Master Gardeners from the Snetsinger Butterfly Garden Habitat Project located in Tudek Park in State College, PA. At the SBG, we're all about the stories, tales of those fascinating interactions between plants, pollinators and people.
Lisa:Well, Pam, spring has sprung and Arbor Day is just around the corner, and our listeners might be thinking about planting a tree to celebrate, because that's what we're supposed to do, and I know there are several events just here in our region which are featuring free tree giveaways.
Pam:We've done that at the SBG. We've given away some trees in the past and it's really a great way to raise awareness of the importance of native trees in our habitats. Trees offer so many benefits to the ecosystem, from filtering our groundwater and preventing runoff to sheltering all those untold creatures in their leaf litter and well, they do so much more right.
Lisa:They sure do. And I think we often think of trees, if we think of them at all, as like specimens, isolated, individual plants, and if one gets cut down, or a bunch of them are cut down, we can just plant some more and it will all be just fine.
Pam:But when you start to understand the life of trees, you realize it's really not that simple. Just like people, trees thrive in communities.
Lisa:And to learn more about that. We are so pleased to be speaking today with Catherine Pugh, a forestry and wildlife educator with Penn State Extension, specializing in non-timber forest products, agroforestry and native plant education. Cat holds regular native plant walks for the community and extends her reach statewide through webinars and other speaking appearances, which is how we came to hear her, as she presented a great webinar recently on tree communication. Welcome, Cat, thanks for being with us today. So maybe we should start by talking about all the ways that trees benefit our ecosystems. I think if you were to ask the average person why we should plant a tree, they might say well, it sequesters carbon or it provides shade and cuts my energy bill. And since we're all about pollinators here, we're always promoting native trees as being so important for pollinators, for example, like bees, who really need that early spring pollen and nectar from trees like maple or willow or oak when they're just emerging at this time of year. But trees do so much more, don't they?
Cat:Yes, so much more so. Trees are great at helping to filter water, allowing that water to get back into the groundwater for drinking. They also provide habitat for all kinds of critters, insects, mammals, birds, you name it. Most organisms rely on trees in some kind of way. Trees, of course, produce oxygen. We're really grateful, as humans, to have plants in our life to be able to give us the oxygen we need to breathe.
Cat:Trees are also wonderful because they provide leaf litter. Our deciduous trees, I should say, provide leaf litter, which are a habitat for all kinds of organisms, and we're, on the pollinator confidential, so often thinking about pollinators. For that leaf litter and sequestering carbon is a great example of something that we're often thinking about, especially in the time of climate change, and most of the time we think about sequestering carbon, and what we're really saying is, when we look at a tree, the structure that you're seeing is all made up of carbon. So that's what's happening. We hear term sequester, but what you're looking at is actually a structure of carbon, and so when plants are actively growing, they're actively taking in more carbon dioxide and so they're sequestering more carbon than they're there. As a grandfather oak tree, providing the best habitat and place for your local squirrel family to live.
Lisa:So young or old, trees have much to contribute to our ecosystem in so many ways.
Pam:In the webinar you talked about leaf litter, and we're always talking about the importance of leaf litter as shelter for chrysalides or cocoons or even food for some caterpillars. Can you talk more about the value of leaf litter?
Cat:Sure, yeah.
Cat:So when you have leaf litter on the ground, it will decompose over from when those leaves have fallen off the trees in the fall until the springtime, and so during that time period those leaves are starting to decompose.
Cat:Sometimes they have helpers with that decomposition, which could be decomposers as organisms that you can see with your eyes, but other times these are decomposers that are actually in the ground, in the soil, and this is where we have this connection called the common mycorrhizal network.
Cat:These are fungi. Mycorrhizae translates to mean mushrooms or fungi on roots, and so these fungi are associated with the roots of plants and they create kind of an underground network connecting various different plants, trees of different species, even all underground, and these fungi and plants are in a symbiotic relationship. So the plants are again taking up that carbon from the atmosphere and creating usable sugars, the energy sources, and then moving those into the roots, where the fungi are able to access them as a food source, and the, on the flip side, the fungi are able to access them as a food source and, on the flip side, the fungi are able to kind of mine these nutrients out of the ground, from those leaves that were previously on the surface that have decomposed into the soil. The fungi are able to pull those nutrients out and pass it back to the plants.
Pam:Say, I just planted five trees close to each other, how can I encourage fungal growth that will help the tree community?
Cat:Well, you don't have to do much. Just leave the leaves and that'll go Well the thing is that these mycorrhizal networks are already existing in the landscape, and so, especially if you already have some established plants in your landscape, those networks are probably already there, and so if you're planting trees near something else that you've already had in your yard, it's likely that there's a network that already exists, and at some point, the network will extend to those plants.
Lisa:So how about, in a typical suburban type scenario that I'm thinking of, say, I've got a little lawn of fill dirt and the turf grass and not much else around and I plant my little Arbor Day sapling in that lawn with a little ring of mulch around it? Is it going to be okay with no network that's nearby that it can hook into?
Cat:Well, good news is is that those trees were probably growing in some kind of soil that might already have some of those mycorrhizal networks, so in that case not much else would need to be done. There are some commercial products out there that are sold for mycorrhizal establishment. I've done a lot of digging into this and it's tricky to say how effective those are. In some studies it was found that, you know, something bought over the counter wasn't really establishing a network on the plants, but compared to a solution that was made in the lab, that mycorrhizal network was able to be inoculated into the plant. So perhaps it had something to do with the way that the product is stored, that it wasn't having a big impact on the plant itself.
Cat:In other cases it was just depending on the type of product and how it's being sold if it's sold as a suspension, so a liquid, or if it's sold in some other dried form and so found that various types of products and the way in which that they're sold might have an impact on how successfully those kinds of mycorrhizal networks will be inoculated into the plant. So, all that to say, I haven't found any studies that had negative impacts from those products. If anything, maybe you'll see some positive responses, Maybe you'll have more vigorous growth in those plants or nothing will happen, and so, yeah, it's tricky. Most of the time, those networks are already established, especially if you're getting plants that are coming from a nursery setting and you mentioned free plants. But if you're getting something, say, at a nursery, and it's much larger, those plants are typically grown in the ground, and so in those cases, the mycorrhizal networks are probably already well established.
Pam:Well, that's good news to know that if you create the right conditions, it's just going to happen naturally. I think sometimes, as humans, we feel like we need control.
Lisa:Right, we have to do something. We have to do something to make it better when actually nature pretty much has a handle on it.
Cat:Yeah Well, and this is such a still new area of study, the person who kind of came up with this and discovered this underground network, her name is Suzanne Simard and she published her work just in the early 2000s. And her book Finding the Mother Tree talks all about this, and so you know there's a lot to still learn on this topic, and so maybe 10 years from now, we'll come back to this podcast and say, oh man, Cat was so wrong. I guess we'll find out.
Pam:Well, we have found that about pollinator education how much it's changed.
Lisa:Just in the past 10 years.
Pam:Yeah.
Lisa:Yeah.
Cat:So to be continued maybe.
Lisa:Yes, bring it back in 10 years, so obviously we want happy, healthy trees around us and we want to do the best we can with planting them. So it's really great news that the mycorrhizal network will already probably be present there, and I think it would be helpful for us to know a little bit more about how they communicate their needs, and in your recent webinar, Cat, you described how trees are communicating all the time, both above ground and below ground.
Cat:Yes, and I talked about different ways they're communicating, based on a study that used this great analogy where plants are communicating wirelessly above ground, where they're sending chemical signals to one another through volatile organic compounds, and then they also compared it to below ground as the wired communication, and that's where that common mycorrhizal network, that combination of fungi and roots, are happening, where they're physically touching to send signals and nutrients and water and all kinds of things. So, above ground, that wireless communication, it's happening in the air and so these compounds are being sent in the air and often are happening in response to some kind of usually herbivory event. Something is coming and munching on a plant and there's some interesting debate about you know what is the motivation behind these signals being sent is being sent? Some folks think maybe it's happening as an altruistic case, saying one tree is being attacked by an herbivore and they're sending a signal to the neighboring trees to let them know hey, put up some defenses, I'm getting attacked as an act of altruism, with no expectation in quotes here it's plants but no expectation of returning that favor.
Cat:Perhaps the signs are also being sent as a mutualistic motivation, so if I'm a tree being attacked I might send a signal to my neighbors to let them know, and there's an expectation that in the future that favor will be returned. Or perhaps it's happening because it's just eavesdropping on neighbors, right? So if I'm the tree being attacked, I might be sending some signals just because my leaves are getting damaged and it's just volatile chemicals that are emitting in the air. In the air, no other motivation but a neighboring tree might just notice that these chemicals are in the air and recognize it as a stress scent, for lack of better words, stress chemical, and so that way the neighboring plants can get ready themselves for that attack.
Cat:So this is an example of just why maybe the signals are being sent, and that's kind of difficult to study when we're talking about communication. This is often happening in community, in a forest. If you were truly trying to just pinpoint the above ground communication, you'd have to eliminate any below ground communication and just imagine trying to isolate and make sure no roots and no fungi are touching each other below ground. So there's no signals being sent below ground and only above ground. So this is truly a difficult topic to study, to know deeply what's going on if we're thinking through the lens of motivation.
Lisa:Right and it's hard not to assign human motives to it.
Pam:So I have a question If there's, say, an organism munching on a leaf, like you were saying, would the communication be between the same species? Because usually that insect has evolved with a certain species. So is there communication among other species.
Cat:That's a great question. So it's been found that con-specific or same species plants are better at noticing those chemical signals for that reason that they do have the same herbivore predators. But it also has been found that maybe it's more important that the plants have similar info chemicals. So that means they produce similar kinds of essential oils as these defense chemicals, and so they don't have to be the same species. They just have to produce similar enough chemicals that it can be recognized so maybe in the same plant family.
Lisa:There's a lot going on out there. eople yes, there is.
Cat:Yes, it's all around us too, and we're just not noticing.
Pam:Well, you had said you lived in the woods. I do so? Do I s Since your talk? I just look out there and I think of everything that's happening, because the trees are so close together.
Lisa:or singing osomething like that. So that's above ground. Now tell us more about what's going on down there below the ground.
Cat:Yes. So this mutualistic relationship that's happening where both parties are benefiting the plant and the fungi and in fact, depending on which source you're reading, it's between 80 and 90% of plants have an association with mycorrhizal fungi. So most plants out there have these connections on their roots that are then creating communication mats underground. And what's happening is these fungal common mycorrhizal networks are able to share nutrients from one plant to another. They're able to share infochemicals, so they are able to share nutrients from one plant to another. They're able to share info chemicals, so they are able to send signals underground and they're able to share things like water and whatnot.
Cat:It's been found that some plants are sharing more resources with younger plants. So if you have a mature tree and underneath that tree is a sapling, it's been found that more nutrients are shuttled to the sapling. But it's interesting because I think in the webinar I might've posed it where it was the trees were doing the shuttling, like the mature tree to the younger tree. But I've recently talked with a colleague of mine who studies roots and she mentioned that perhaps it's actually the fungal network, like the fungus itself, that is pulling the nutrients and shuttling it to the sapling, because I mentioned earlier that those newer, younger plants that are vigorously growing are sequestering more carbon, and when that's happening they're producing more sugar, and so perhaps it's the fungi that are influencing the movement of the nutrients so that, in return, they're getting more sugar too.
Lisa:Well, see now, that really messes up our human perspective, you know of oh, the mother tree is helping the baby tree.
Pam:Such a nurturing activity yeah. So it's very complicated and unclear.
Pam:So living in the woods, it's fascinating to observe how a tree slowly dies, the branches on the top start falling down and then the bark comes off, the slow decay and then the wildlife that takes up residence in either a snag or a fallen tree. So what are some of the other benefits of decaying trees? Because we're trying to encourage people to leave snags for pollinators, because it is ollinator confidential. But as far as other reasons, why is it great to leave a tree if it's not going to fall on your house?
Cat:Right, that's what I always say too. If you can leave the snag, please do so. Any time a plant is decomposing, those nutrients are going back into the soil, so that's great For wildlife. I know you mentioned it, but I want to touch on some of my favorite organisms that use snags. So there's all kinds of birds that will use snags. Certainly, woodpeckers create cavities, and after the woodpeckers create the cavity, other organisms will come in and use that space too. You also have native bats to Pennsylvania that like to slip underneath loose bark and use that as a roosting site, and there are all kinds of insects that will live in those snags and use it as food and cover.
Lisa:And you mentioned bats, just so our listeners know, that's your best mosquito control ever is bats. So we want to encourage those bats.
Cat:Yes, and certainly owls will use snags as well as roosting sites and also it's just a great place for a perch for all kinds of birds. So we want to leave different structures in our forest. So I always am talking about forest layers when I'm, you know, explaining what a healthy forest looks like. And so within that forest layer you have the herbaceous layer on the ground. Above, that is the shrub layer Above, that is the understory and then the overstory, and then you also just want some extra structure. So all organisms need food, water, space and cover. Organisms need food, water, space and cover, and a snag can be a lot of those things for a lot of different organisms. You know it's certainly cover, it's certainly space. You know, when we talk about vertical structure, space is something that I don't think people always think about, because we have organisms that occupy, say, the same snag, but it will only occupy the bottom of the snag and others will occupy inside the snag and others the very top. So having any kind of vertical space in your forest or landscape is great.
Lisa:It's like a multi-use high-rise, that's right.
Pam:I was at a Master Gardener conference in Portland and there was a gentleman there who talked about sculpting snags, and I love a good snag. They are so naturally sculptural and, of course, provide vital habitat. Of course you want to make sure it's not a hazard if you want to have a snag on your property. That means removing trunk and branch portions in danger of falling on people, structures, power lines and so on, and you can even take those trunk and branch portions and put them in another area of your property. As a matter of fact, the arborists at the Mount Cuba Center in Delaware make an art of trimming dead trees to create these safe, natural-looking snags dead trees to create these safe, natural-looking snags. And you can blend it into the landscape by even training some native Virginia creep or another native vine to climb it. So we are not only going to leave the leaves, we're going to save the snags.
Lisa:I think we need a t-shirt that says that, okay, there's somebody out there and there's a business opportunity just waiting to happen. Yeah well, we're always preaching the layered landscape for pollinators, of course, because each layer has something to offer different pollinators, and it is the same for all wildlife, really, in landscape, and even each layer, and level of historic disturbance in a forest is pretty important too, isn't it?
Cat:Yes. So when we talk about forests, I always advocate for mixed age stands, meaning you have trees of different age classes. So in that case you have plants that are saplings growing into the forest and will eventually take over as the overstory trees. Then you have mature trees that are already in the canopy, and the reason you want these mixed age stands is because it creates even more habitat for diverse communities. So there are certain bird species that rely on those mature overstory trees. Without that type of tree, they would not be able to live in that space. But likewise you can say this for every layer below. So there are certain organisms that need that shrub. Then the shrub layer is so important because it creates a food source, diversifying food source, but it also creates different structure and cover. So if you think of all kinds of our small mammals, that's a great place to hide from predators and then be able to scurry out to get food somewhere else and then come back for cover. And so we want to think about forest management in a way that we're creating these diverse stands of different age classes, and so we don't want to do a clear cut. Certainly, there are times when small clear cuts are appropriate and I can talk about that in a minute. But we want to be mindful to have different age classes within a stand and a diverse group of plants within a community within a stand and a diverse group of plants within a community. And so that also goes back to the common mycorrhizal network, because there are two types of this underground network that exist and they kind of come together in a lot of ways.
Cat:But there are what's called ectomycorrhizal fungi and, as the name suggests, ecto means on the outside and mycorrhizal means fungi on roots. So these are the fungi that are only on the outside of plant roots, and this kind of mycorrhizal fungi has the ability to extend far. Certain species have more of a network than others, but anyway that group is able to mine nutrients out of the leaf litter in a more efficient way and that's great for the plants. But then you also have this other type of mycorrhizal fungi called arbuscular mycorrhizal fungi, and this is intercellular, so those fungi get into the plant cells in the roots and that group is able to colonize.
Cat:A lot of times herbaceous plants will have that type of association and they cannot mine the nutrients out of the soil, so they have to rely on anything that's already in the soil, and what's important here is that there are certain plants that can only have ectomycorrhizal fungi and others that can only have arbuscular, and so when you have a diverse plant community, they're able to link up in interesting ways and benefit the whole forest community, and so thinking about these mixed age stands means that you have more opportunities to have more underground network connections, more communication can happen and they're able to take up nutrients in different ways. So you want to be thinking about having those different layers and, like I said, herbaceous plants often have the arbuscular mycorrhizae, which aren't very good at mining the nutrients. So if you have them in combination with those plants that, like a lot of trees, have ectomycorrhizal fungi, they can benefit and share those nutrients better.
Pam:Another reason to have layers Exactly.
Lisa:We're always preaching layers, layered landscape for pollinators, but this gives us a whole other reason that layered landscapes are a good idea.
Cat:Yes, and I mean when you have diverse plant communities, then you can support more organisms in general, more pollinators, and so there's more food sources available. So if you think about all of the early spring flowering trees in Pennsylvania, you want to make sure you have a diverse community so you can support that group of insects. And then as you go down the chain, the more insects you have, the more food sources. You have a diverse community so you can support that group of insects. And then as you go down the chain, the more insects you have, the more food sources you have for everyone above them in their food network. So insects are the, and caterpillars in particular are the most important food source for new birds. You know young birds coming up this spring.
Pam:We talk about that a lot, I be.
Cat:.
Lisa:So below-ground communication is happening all the time between lots of plants, and it's not just trees that benefit, but the above-ground chemical communication that's going on also all the time and we have no idea that it's happening. Is that only happening between trees?
Cat:No, it's happening between trees and understory plants as well, done by some Finnish researchers, looked at a sub-Arctic forest community and found that there is an interesting communication happening, or chemicals are being transferred from this marsh Labrador tea. It's a type of rhododendron, it's a shrub, and the chemicals are coming off of the rhododendron and are sticking to the underside of the leaves of the mountain birch trees in the same forest community. Just for some context, these Rrhododendrons like our native rhododendron in Pennsylvania. It's not used by many insects as a food source. It's not palatable. It has some toxic compounds that deter organisms from eating it, and so that's the chemical that's attaching to the undersides of these leaves of the mountain birch. And so that's the chemical that's attaching to the undersides of these leaves of the mountain birch. And it's happening at low temperatures. So once it starts to warm up in those locations, those chemicals are then being emitted into the air as volatile organic compounds.
Cat:And when that's happening, the herbivores of the mountain birch, its usual predator, is then not able to recognize the plant as a food source because it's getting the signal that it's a toxic plant. Right, it's? That organism doesn't eat rhododendron and it sure doesn't want to eat this camouflaged rhododendron here. So that is an example of chemical camouflage. So it's a benefit to have communities, forest communities, with diverse groups of plants, shrubs and trees, and especially paying attention to groupings of plants that can benefit one another. So in this case they found that those mountain birches experience less herbivory than other mountain birches in the absence of rhododendron.
Pam:It really is amazing how they are cooperating all the time.
Lisa:So, listeners, we hope you're thinking of planting a tree in a whole new way now. Learning how trees interact in forests can help us have more success in our own landscapes, and even if we don't live in or near a forest, we want to keep in mind the importance of layers, and it's easiest to start building those layers when a tree is first planted. So, rather than just planting that tree all on its own with a ring of mulch around it, why not start with a community by adding more than one tree?
Pam:or maybe a shrub or two, or some ground level perennials or ground cover to start building up those layers. For example, you could add some eastern ninebark or one of my favorites, spicebush, or virginia sweet spire, and you can add some herbaceous layers like tall penstemon or wild geranium and golden ragwort. Oh there's, there' so many. It's like trying to pick your favorite child. There's so many to choose from, because you want to provide food and shelter for so many different wildlife species. So something I did when I moved into our house in the woods is I walked along the stream to see what was already growing here, what were the plants that were here in this area, and that was very helpful. That's where I started, because if they succeeded along the stream, they probably would succeed in my place. So that's a good way Take walks, become inspired.
Lisa:Although avoid the invasives.
Pam:Oh yes, of course we have a lot of those too Slowly removing those.
Lisa:So if it's green in the very early spring, probably not one that you want to propagate.
Pam:Get a good plant app so you can identify what you're looking at. It takes time, but you finally get it and consider using leaves or compost to retain moisture and inhibit those weeds, rather than mulch. I don't like the word weeds. We call it editing instead of weeding. Remember just one inch of hardwood mulch is as impermeable to ground nesting bees as pavement and it doesn't support the life cycles of countless creatures the way leaf litter does.
Lisa:So there you go, some good ideas to get you started on your very own richly diverse layered landscape, because planting a tree is a great idea and planting more than one is even better. So thank you so much for being with us today, kat, thanks for having me. And listeners, be sure to check out the Penn State Extension website for the Forestry and Wildlife Newsletter, and you'll find more about how to create your very own layered landscape on our website, snetsingerbutterflygardenorg.
Pam:And there is the Cente County Master Gardeners Plant Sale at the Ag Progress Day site May 18th, and there will be a selection of native trees and shrubs that you can purchase for your landscape.
Lisa:Thanks for tuning in today. Now get out there and plant some trees, preferably more than one, and join us next time for more Pollinator Confidential. https://extension. psu. edu/forestry-team-sign-up