What is Forest Fragmentation?

Dan Herms, vice president of research and development at the Davey Institute, discusses what forest fragmentation is, how it affects wildlife and your community, and what can be done about it. 

In this episode we cover:

• What forest fragmentation is and the impacts (0:33)
• What can be done? (3:59)
• Connecting of the fragments (7:21)
• Urban planning (8:45)
• How Dan started learning about forest fragmentation (9:27)
• Wooster Memorial Park (10:52) (19:04)
• Invasive species (12:05)
• Garlic mustard (14:14)

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Transcript

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Doug Oster: Welcome to the Davey Tree Expert Company's Podcast, Talking Trees. I'm your host, Doug Oster. Each week, our expert arborists share advice on seasonal tree care, how to make your trees thrive, arborists favorite trees, and much, much more. Tune in every Thursday to learn more, because here at the Talking Trees Podcast, we know trees are the answer.

This week, I'm joined again by Dan Herms. He's the Vice President of Research and Development for the Davey Tree Expert Company in Kent, Ohio. Today we're talking about something that I know nothing about, and I am looking forward to learning about it called forest fragmentation.

Good morning, Dan. How are you? Tell me a little bit about what that is.

Dan Herms: Well, good morning, Doug, and I'm doing well. Thank you. I'm glad to be here this morning. When forests are cleared for agriculture development, so forth, that often leaves small pockets or islands of the remnant forest, isolated patches of forests. We call these forest fragments.

Doug: From your standpoint in your studies, what does that mean for the forest?

Dan: Well, fragmenting the forest has a multitude of impacts that change the nature of the forest from what it was as a large intact forest. For example, one of the biggest and maybe most obvious effects is that there's a lot more edge habitat to a forest fragment and much less interior deep forest habitat. The ratio of forest edge to forest interior is much greater in a forest fragment. This has a lot of important implications for the habitat, the biodiversity, the environment. At the edge of a forest, there's more light.

The temperatures are higher, soils are drier. The ground vegetation is different. Often more chubbier, more woody vegetation. In the interior forest, it tends to be more open, it's cooler, moisture environment. It's very different. These have really important implications for biodiversity and wildlife. The forest edge, for example, is much more susceptible to invasion by exotic plants. Invasive plants for the most part don't tend to be shade tolerant.

They need more lightings like multiflora rose, honeysuckle, these kind of things we're probably familiar with. There's more generalist animals: deer, raccoons, blue jays, these kind of things. The species that are adapted to the interior forest don't do as well. Think salamanders, flying squirrels, these kind of things are just not going to find on the edge and as abundance.

Then there's more predators of birds and things around the edge. Domestic cats, raccoons, cowbirds. Cowbirds parasitize the nests of native songbirds and that has a negative impact. The cowbirds don't tend to be deep in the forest, but they're an edge species.

Doug: It just makes sense that when you change a big expansive forest in that manner that it's going to certainly affect the environment, affect the wildlife in there. What do you think can be done about it though? Is there something we can do? Should we plan differently? Would that help? When you hear the word clear cut, you think Amazon forest, but that's what you would do here. You'd probably clear cut the forest for a new development or something. I guess, right?

Dan: Well, that's what's happened over time. Think about the urban environments. Over years and years, the forest has been cleared away for buildings, and it leaves these woodlots and isolated forest patches, and you see those on the agricultural landscape too, where you'll see a woodlot that's surrounded by large agricultural fields. It's a process that happens over time. What can be done? There are things, and I will say that forest fragments do have benefits, especially in urban environments for biodiversity and so forth.

If these fragments can be connected, studies have shown that this enhances the biodiversity, the number of species that reduces the risk of local extinction. Forest fragments can be connected by corridors, say riparian corridors, even utility right away. Corridors can serve as a connection that animals and plants can disperse along. They can be connected, it can reduce inbreeding as the populations spread. The shape is really important. Let's say a 20-acre woodlot, if it's long and narrow, all of that will be edge.

If it's round or square, there'll be a acre or two in the interior that is really characteristic of an interior forest habitat. Trying to reduce the amount of edge is important and the more a forest fragment resembles and has the characteristics of an interior forest, the more benefits it will have for things in the urban environment, reducing urban heat, purifying rain water and reducing runoff, storing carbon, providing a refuge for biodiversity, insects, plants, birds, small mammals, these kind of things. In the urban environment, woodlots provide a really important refuge for migratory birds, a way station where they can rest and feed as they're traveling to and from their breeding grounds, for example.

Doug: You mentioned a lot of interesting things in there. I was wondering about the connecting of the fragments. Is that done by tree planting, or how is that done? If you connect them, does it have to be like a solid forest? Just fill me in on the connection part how that works.

Dan: There are different ways that fragments can be connected, but the ideal would be a forest corridor, say something that's preserved along a stream or something that could connect one corridor to another. It could be a planned corridor, a rail trail that maintains, for example, a tree environment that's wide enough to provide a corridor of sorts for birds and butterflies and things. Maintaining a utility corridor in such a way that it has some habitat, tree habitat on the edges, native plants growing in the corridor, in the right of way, these kind of things. Linear parks could be designed in such a way to provide a corridor.

Doug: I have to think that in city planning, urban planning, even suburban town planning, that this is something that should be considered and is it being considered?

Dan: Increasingly, it is. The importance of corridors, wildlife corridors is recognized and is being incorporated into habitat management. Was at a conference and there was a whole symposium on establishing corridors to link habitats, for example, and creating a network of corridors and fragments.

Doug: Is this something that you started to study? How would this come into your realm?

Dan: I'll say I started studying it when I was a child, and I think that's another benefit these urban woodlots, there was one close to my home, and we explored and played and looked for creatures. To us, that was the wilderness, and then in college I studied forest ecology, and fragmentation was a big part of that. When I was a professor at Ohio State University, we did a lot of research in forest fragments. For example, studying the effects of emerald ash for ash mortality and forest fragments, what impact that had on amphibians, what impact that had on birds, on invasive plant species.

I've had a connection with forest fragments for a while. My wife and I are involved in a local park that is a green space, a green island of forest in our city, and trying to enhance the benefits of that, reducing invasive species, looking at butterfly conservation, and so forth.

Doug: If you could, I know a little bit about the town that you live in. Explain, if you could, just what size town that is, and then how big is that area for that town?

Dan: I live just outside of Worcester, Ohio, and it's a town of about 23,000 people. The park that I'm referring to is called Worcester Memorial Park. It is now over 400 acres in size. It's a large green area. If you look at Google Earth, you see it's one of the largest green islands in this part of the state. It is big enough that it has some really nice interior forest habitat and the wildflowers, the wildlife, and so forth that you might expect the owls, other species. It's a really nice habitat. It's isolated. It's an island, but it's a large island.

Doug: I'm glad you mentioned that because I'm just picturing a one acre square in the middle of the town, but 400 acres is huge. Talk a little bit about the invasive species and getting them out of there. Is that important?

Dan: It is really important. The volunteers, the friend's of Worcester Memorial Park, have been very active in removing invasive species. In cooperation with the city that owns the park, the volunteers have engaged in campaigns to pull out the garlic mustard, for example, which is an important invasive species, eliminate the multiflora rose, the honeysuckle, the autumn olive. Those are probably the biggest problem species in that park. The garlic mustard is an interesting example because it is invasive species.

There's an endemic butterfly in the park called the West Virginia White. The West Virginia White exists in these isolated patches. Most of its large forest habitat has been broken up and fragmented. There's a really nice population of the West Virginia White. West Virginia White's native host plant is a plant called cut leaf toothwort. It's a native wildflower, but it lays its eggs also on garlic mustard. This is not a good thing because the larvae cannot survive to adulthood on garlic mustard. The butterfly gets tricked into laying its egg on a bad host plant. It's an ecological trap. Eliminating the garlic mustard has been really important for conserving this species. It's a species of concern. It's not endangered, but it's a threatened species.

Doug: Let me see if I have this right. That's not the right plant for the butterfly to lay its eggs on, because when the larva emerge, they can't eat it, right? They wouldn't want to eat garlic mustard. Is that right?

Dan: They'll eat it, but they get sick. This is work that a friend and colleague of mine, Don Cipollini, Professor at Wright State University in Ohio, has studied with his graduate students.

Doug: This is one thing that people could do to help in their own communities to find an area like that, or any area you could find, and work on getting rid of something like that garlic mustard. You guys down there need to have a garlic mustard festival when they're in the rosette stage, and turn that into something you can eat, get it all out of the forest, and make pesto out of it?

Dan: Garlic mustard is an edible plant, and it's thought that it was brought to the United States originally as a garden herb. I have seen recipes for garlic mustard.

Doug: I hate to say this, but I've made it into pesto before. It's such a pain in-- I just live on a four-acre patch of forest, and I spend a lot of time pulling that stuff out, because I don't want it in the forest, and especially now, after hearing that it's fooling that butterfly. I spend a lot of time, especially at that first year when it makes the rosette. If I see it, I want to get rid of it. If you don't mind, talk a little bit about its life cycle so that people know how to deal with it. In my opinion, I love to get it at that rosette stage. You don't always get them at that stage, but I got to get to it before it's at seed.

Dan: Garlic mustard is an herbaceous perennial, very shade-tolerant, moist soil. It does very well in the interior forest. It's an invasive plant. It can crowd out the native wildflowers. The life cycle is that has a typically a two-year life cycle. The first year it germinates and grows into a rosette, and it will overwinter. You go out in the forest, and you'll see the green rosettes during the winter time if they're not covered by snow. Then the following spring, they'll bolt.

By that, I mean they'll grow very fast, a long stalk with white flowers happens very early. They're already blooming in Ohio. They produce seeds and they wither away pretty rapidly. That's the problem. You have to weed them very quickly in the spring, oftentimes when you're busy with other things.

Doug: Exactly. You're overwhelmed with the garden. This is me. I'm overwhelmed with the garden, but if I see those blooms, I'm after it. If I just spend an hour or two pulling, it will save me so much the next year.

Dan: Yes. For those folks that are not averse to using herbicides, you can actually treat the rosette during the winter time when it's green and the other plants are not present. The wildflowers are gone. Studies have shown that you can treat with glyphosate as long as the temperature is above freezing, so it doesn't freeze in your sprayer. Spray in February, January. You won't see any real effect until the following spring. The plants will wither away rather than bolting. That can be an approach for clearing large areas. One of the advantages, and to get back to your original question about the small woodlot, is that you can make a difference pretty quickly in terms of eliminating invasive plants.

If you have four or five acres, you can get in there. You can eliminate the invasive plants. You can reintroduce new plants. You have a very tractable, manageable chunk in which you can have some real benefits in terms of enhancing biodiversity, restoring some of the natural, ecological interactions and species.

Doug: With your park there, why you to be part of that project? You have a lot going on. You're a scientist. You're studying this. You've got working for Davie. Why you to be part of that project on that 400 acres?

Dan: That's just a really good question. My wife is the President of the Friends group.

Doug: That helps.

Dan: That helps. She's actually written six grants to the state of Ohio. It's called the Clean Ohio Grant Program, which has purchased about 250 acres that has increased the size of that park dramatically. It's just a wonderful place to hike and we have just felt it's a valuable and worthwhile thing to be involved in.

Doug: Well, Dan, I'm going to leave it right there. That is so awesome. That is so good. As always, thank you so much for the information. I love picking your brain. I was worried about this topic because I don't know anything about it. I knew if anybody could put it into perspective for me, it was you, Dan. Thanks again for being part of the podcast.

Dan: Oh, you're welcome. It's always a pleasure, Doug.

Doug: I always learn something new when talking to Dan and good for him and his wife for helping their local park. My brother lives in Columbus. That might give me an opportunity to actually see that forest. I'm intrigued.

Tune in every Thursday to the Talking Trees Podcast from the Davey Tree Expert Company. I'm your host, Doug Oster. Do me a favor, subscribe to the podcast. We have a lot of fun as we cover these important topics. As always, we'd like to remind you on the Talking Trees Podcast. Trees are the answer.

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