Episode 13: Plants and Wildlife Occupying Utility Rights-Of-Way w/ Penn State’s Dr. Carolyn Mahan

Welcome to the 13th Episode of Trees & Lines: Fresh Perspectives on Utility Vegetation Management!

Trees and Lines Podcast – Episode 13

A conversation with Dr. Carolyn Grace Mahan – Professor, Pennsylvania State University and researcher at State Game Lands 33.

Tejpal Singh, COO, and Dr. Phil Charlton, Principal Advisor, at Iapetus Infrastructure Services


Philip Charlton: Welcome to another episode of the Trees & Lines podcast. Today, Tej and I will be speaking with Dr. Carolyn Grace Mahan, a professor at Penn State University and a leading researcher in the study of the effects of management on plant communities and wildlife occupying our utility rights-of-way. Dr. Mahan leads the State Game Lands 33 research project, which has guided our industry for 65 years. Have a listen. Hope you enjoy. 

Welcome Carolyn. We really appreciate you joining us for the podcast. Why don’t you start us off by telling us a little bit about yourself and about the research there at Game Lands 33.

Carolyn Mahan: Well, it’s nice to be here, Phil. My name is Carolyn Mahan. I’m a professor at Penn State of biology and environmental studies and I research a wide variety of ecological issues, including anything from squirrels to powerline rights-of-way that I have been working very closely with since 2014. This project started in the 1950s and I’m just one of the latest in a long line of researchers who have worked at State Game Lands 33 in central Pennsylvania.

Managing ROW Habitats to Increase Biodiversity

What we’re trying to understand is how can the industry manage habitat under rights-of-way to increase biodiversity and allow wildlife to persist in those types of environments. The electric transmission industry manages the actual habitat and has provided research funding over the past 65 years. In addition, there have been matching funds provided by the universities in which the researchers are located. For example, we always have students working on these projects.

There is now a growing interest in these societal environmental goals that industries (e.g., power industry, habitat management industry) like. They are interested in showing that they are beholden to the public and how they manage habitats.

I think that is why the interest has moved away from just hunters, who are becoming a smaller and smaller part of our population, to this overall idea of biodiversity and how habitat has provided for biodiversity, which is the diversity of all living things (e.g., plants, insects, mammals, and birds). And that is of more general interest to the public.

There has been very good cooperation and interest from the funders moving beyond game species.

Origins of State Game Lands 33 with Hunters’ Concerns

Philip Charlton: For 65 years, this is by far the longest ongoing research project.

Carolyn Mahan: Yes, we’re just passing 65 years and the research project started.

When powerlines going through state game lands, which are publicly owned lands here in Pennsylvania, were getting constructed in 1950s, hunters who used the game lands were concerned about the effects and how maintaining the habitat under the power line would affect game animal populations.

Hunters were concerned that perhaps herbicides needed to control vegetation growth would hurt populations of game animals. When the project originally started, the focus was on game species like deer, Eastern Cottontails, and Wild Turkey. We’ve since expanded that research looking at non-game species, including pollinators and, most recently, ground beetles.

Key Takeaways

Philip Charlton: 60 years nets a lot of results.

Carolyn Mahan: Yes. There’s a lot of data with this project.

Philip Charlton: For you personally, what are the big takeaways?

Carolyn Mahan: When you manage habitat in these human landscapes, there are two objectives. The first objective in this case is for safety.

There are regulators who make sure that the area underneath rights-of-way is cleared of trees. Your listeners understand that as trees grow up into rights-of-way, they can interfere with the transmission of electricity and harm the transmission lines. So, you need to ask the question, what is happening with the habitat in terms of power transmission. But then also, how is the habitat managed? Is there a way that we can manage the habitat, that also can improve the landscape for wildlife? And my big takeaway is, yes, we can manage that landscape for wildlife, particular species of wildlife, particular groups of wildlife, and we can do it successfully.

It requires professionalism, dedication, and knowledge of the landscape to do it properly, but it can be done.

Management Strategies

Philip Charlton: What are the management strategies you’ve looked at? Herbicide use, mowing, and mechanical?

Carolyn Mahan: I’ll try to explain the study design, Phil, because it is one of the things that makes this so special from a research perspective (beyond the fact that we have 65 years of data). If you can picture, this transmission right-of-way is almost three miles in length and about 200 feet, at least, in width. These are the big towers that carry electricity over long distances. And the right-of-way itself runs through a forested landscape, an Appalachian forest. It’s wide and two miles long and within that we have replicates of different types of vegetation management strategies.

We are able to replicate these strategic approaches that have been tested on State Game Lands 33 including hand cutting (where you just take down the vegetation using chainsaws by hand), mowing (i.e., larger mowers than people would use in their yards), and different types of integrated vegetation management approaches that use herbicides.

We use high-volume herbicide application where it’s non-selective (i.e., you just spray the area with herbicide when the plants are getting too high and might interfere with the power lines) and other approaches that are very selective.

Of the two selective herbicide approaches that we are looking at, one is called low-volume folio where the leaves of non-compatible plants are sprayed during the growing season. They’re sprayed and removed. If you see a red oak seedling emerging, you spray that red oak seedling and remove it from the rights-of-way.

The other selective approach is called basal low volume, where instead of just spraying the entire plant, the woody plant is cut and then herbicide is applied directly to the stem. In my opinion, the basal low volume is the most selective application type of habitat management that we perform on the rights-of-way.

Philip Charlton: Relate that now to your biodiversity studies and impacts.  

Carolyn Mahan: Okay, so I always have to make this very clear to listeners or researchers who I work with. Each technique can promote different types of wildlife.

I’m going to start with hand cutting first because hand cutting is a great method for developing brushy woody habitat. And there are species of wildlife that really like brushy woody habitat, for example, Appalachian cottontails and red-eyed verios which is a type of bird. They thrive in that habitat. That habitat, however, is not compatible with rights-of-way because we have oak trees that grow over time and have to be cut. It costs a lot of money to maintain.

From a biodiversity perspective, if you’re managing for those woody vegetation species, it’s fine, but it’s not compatible with the rights-of-way. What we have found, however, is that instead of woody vegetation that regrows, these selective herbicide applications create a field-type environment dominated by forbs and low-growing shrubs.

So instead of the woody trees and oaks, you have a field of goldenrod, Astras, and rubus blackberries coming back. And they support a different assemblage of biodiversity, like native bees, grassland breeding birds, and snakes that need access to sunlight for basking along with rare species of forb plants like yellow loosestrife and woodland lily.

So as far as biodiversity, all those approaches support wildlife, but it’s what is most compatible with the powerlines and also can support a diverse native community.

There is one approach that is the least beneficial for biodiversity, and that’s the non-selective herbicide application. When herbicides are applied at high rates, non-selective, they remove all vegetation, whether it be woody or forbs. Of course it, it reduces the diversity of the native plants To tie it back, the selective herbicide approaches promote the most biodiversity. That is also compatible with rights-of-way.

From a practical perspective, if I was working for the industry, I can make conclusions from my research area, which is an Appalachian forest. I’m not quite sure how there’d be other challenges managing another habitats, especially places like the South where they have a very long growing season or the West coast where they have to deal with fires.

The Cost of Resetting the Habitat

I will talk from our perspective. One of the greatest costs to this type of approach is the initial cost when a company initially moves from mowing to a selective herbicide regime because they will have to reset the habitat.

They may have to go in and do a selective herbicide spray first and knock back the vegetation. Then it’s very important over the next five to seven years to have trained crews who can go in, target, and remove the non-compatible vegetation. It’s all about identifying non-compatible vegetation.

I keep using oak trees. They’re a great example in our part of the world of letting compatible vegetation grow (e.g., Mountain Laurel, Allegheny Azalea, Witch Hazel). You need some level of expertise.

Then what we see after about seven years is the habitat starts to stabilize. You start to have this more stable environment of shrubs and forbs that you don’t need to treat as often. And those plants help keep the non-compatible trees from growing through.

So the initial cost can be high and that’s one of the challenges with this approach. To start, you have to put in higher investment but over 60 years, your investment is quite low. When the industry comes back to our study sites to treat them, they use very little herbicide because the selective sites have stabilized into this early successional shrub for habitat that you don’t need that much effort to maintain.

But the beginning is going to require an investment. Money is related to this in expertise. You need people who can identify the plants. My research and others’ work has shown that, after that initial period of time, the costs decline dramatically because you have achieved that early successional, native habitat that can be maintained with much lower costs than yearly or every other year.

Philip Charlton: You said seven years. Is that based on three treatments or truly seven years?

Carolyn Mahan: Every site is different. I’ll use our research as an example. In the beginning, if removing woody vegetation, you may have to go every other year, every two years.

In the beginning, it might be quite a bit of investment. You might be using quite a bit of herbicide to reset those plots from mowed or hand cut. But after that five-to-seven-year period, you only need to go back every five years. This is really the rotation they’re following on state game lands 33.

They just go back every five years and in our selective herbicide sites, they spot treat.

In the beginning, it’s going to be much more intensive because you have to knock back those species that are non-compatible with the powerlines to permit the compatible vegetation to fill in and grow.

It does become a partnership with some of these plants. If you have thick shrub cover or very thick forb cover, like a thick cover of goldenrods, for example, those plant communities will help keep the non-compatible plants out of your right-of-way.

Increasing Native Pollinators and Pollinator Diversity

Philip Charlton: You mentioned the Appalachian hardwoods but there’s only one State Game Lands 33. What other research is taking place around the country and how applicable is your research to those areas?

Carolyn Mahan: We just had a conference in October, with a plenary session with faculty from New York State, New Jersey, Jackson State University (MS), Sonoma State (CA), and Ohio State. We were focusing on how to best manage rights-of-way for pollinators. Some of the simple things that came out of the seminar were, if you can increase your cover of forbs, you will increase your native pollinator communities. Goldenrod, Astras and things like Queen Anne’s lace are really good examples of that.

These other sites where they’re doing this type of research are very new. They don’t have 60 years of work, but some of their initial conclusions are similar to what we see at State Game Lands 33. Selective integrated vegetation management is best for maintaining and initiating those forb communities is necessary for high pollinator diversity. It requires training and commitment. One of the biggest problems all researchers have is the disconnect between theory and practice. In theory, from our research, we know that selective integrated vegetation management, and the use of herbicides, for example, to remove non-compatible plants, works.

When we go out outside of our research plots, we all have stories of people coming in and saying they’re doing integrated vegetation management, when really all they’re doing is moving from a mowing regime to a high herbicide, non-selective spraying regime, which removes all vegetation. That is not what we are talking about.

We’re talking about professionals who can identify plant communities and apply herbicides very selectively on a several-year rotation. We see that disconnect between theory and practice at all of our study sites. But the one commonality is that this effort to increase forb cover, flowering plant cover, will increase native pollinators and it works through targeted, selective, integrated vegetation management is a practice in which you can achieve that type of habitat.

Industry Sponsors of Right-of-Way Biodiversity

Philip Charlton: Tell us who your sponsors are.

Carolyn Mahan: I’m very happy to talk about the sponsors. The sponsors of the research are FirstEnergy and FirstEnergy has a lot of subsidiary companies—one of which is PECO in the southeastern part of Pennsylvania.

We also work with Asplundh, which has really been the leader in this project since the 1950s. The Asplundh family has been involved in this research at one level or another, and we’re also working with Corteva Agriscience. We use many of their herbicide products when we do the selective herbicide application.

I do want the people listening to this to understand that at Penn State University, we measure the response to the management. We do not do the management. The management is overseen and paid for by these industry research partners.

Right now, we’re also working with the TREE Fund. They are helping us manage the funding. The industry funding can get managed into a particular account at the TREE Fund, which is a nonprofit organization. Then they work between Penn State and the industry to make sure that the funding happens each year.

Academic vs. Industry Interests

To be honest, as you move through the work from an ecological side, it’s very interesting.

When I present the findings of our work at academic conferences versus industry conferences, industry asks the questions:

  • What is this going to cost?
  • Why should we do it?
  • What benefits will it get us?

Academics are a little bit suspicious that you’re actually saying that herbicides can work. Corteva is funding you and maybe Corteva is making you say that herbicides work. There is that little bit of pushback that I sometimes get from the academic side. But having said all of that, Penn State is very good at setting up agreements whereby, as the researcher, I direct the research and I put into those agreements the freedom to publish and put our work into peer-reviewed journals.

Nothing is hidden, and no one’s ever asked me to hide anything. For industry credibility, the fact that our work is published in very good peer-reviewed journals, and has been for 60 years, gives them the credibility that they need (vs. internal documents, glossy brochures, or PowerPoint slides).

That’s why I like working with industry. I like working with these particular partners in an industry. I’ve never considered leaving academia because I think the fact that I’m in academia gives my work the way that it needs to help industry. If I worked for industry and did this research, I don’t think it would have the same credibility, even though it might be exactly the same.

I also like bringing students in and getting them involved. Every year, we’ve had undergraduates or graduate students involved with the project, and that’s something that I truly enjoy. I also incorporate my research into my classroom.

I think I have expanded students’ minds because a lot of students go into ecology or environmental sciences. They’re dreaming of working for the Nature Conservancy or the Park Service, not Corteva Agriscience to be honest. But then when they see the research and they see the fact that industrial lands make up a big part of our landscape—and the difference they can make if managed properly—I think their mindset changes.

I have mentored students who have graduated from Penn State and are now working for industry, not necessarily in the rights-of-way area. I have students who are working for pharmaceutical companies and helping them increase their sustainability footprint by how they buy plastics for medicine bottles. I had a student who did an internship with FirstEnergy and now he’s working with energy companies not in a direct environmental way but indirectly by improving their sustainability footprint.

And, I’ve had students go on to work for several companies, including Sheetz, which is located here in central Pennsylvania, to focus on how ecology and environmental graduates can work directly with industry to improve environmental impacts from the industrial side. It’s been really rewarding, and those students have made quite a bit of difference in the respective industries in which they work.

Data Collection: Vegetation, Breeding Birds, Pollinators, and Ground Beetles

Philip Charlton: I don’t know if I told you this Tej, but Carolyn got her early start with Drs. Byrnes and Bramble.

Carolyn Mahan: Yes, that was one of the first influences on me that made me want to do this project.

Philip Charlton: One of the first rights-of-way I was ever on was sitting early in the morning with Dr. Bramble listening for birds. And he could hear them. I always shook my head. Did he make that up? No. Birders are a unique group.

Carolyn Mahan: Yes. And we have that aside from vegetation. As far as datasets go, we have the longest data set on vegetation. Vegetation collection goes back to the late 1950s.

The second longest is on breeding birds. We have data on breeding birds at State Game Lands 33 that go back to the early 1980s, I think 1981. We can look at changes in bird communities through time: species distributions and reproductive success.

Philip Charlton: Most recently the focus has been on pollinators. So, what’s next?

Carolyn Mahan: In 2016, we conducted a project looking at native bees. I think most people are aware of the recent work that has indicated that pollinators are declining worldwide and declining very rapidly. And we’re really not quite sure why.

Part of it could be due to human use of chemicals, in particular insecticides that have been used to control agricultural pests which are sprayed often, maybe three times a month, for example, in certain crops.

In 2016, we proposed here at Penn State that we study native pollinators and see if rights-of-way, when managed properly, can be good habitats for native pollinators. Indeed, we found them to be excellent habitats for native pollinators. We found two new state records of native bees. We found the occurrence of the golden bumblebee, which is recognized as a species that may be extinct in 60 years, but it’s doing quite well up on the rights-of-way on our selective integrated vegetation management plots.

My research team presented and published that work. While we were presenting, we would often get questions from other academics who would ask, “What’s going on in the soil?” Maybe herbicides have been accumulating over time and the soil isn’t very healthy. Just because you have flowers and bees, maybe the soil isn’t doing well. We proposed to study ground beetles because they are really important and a viable indicator of soil health.

We started researching ground beetles in 2020 during the pandemic. Right now, we are in the process of identifying those species and looking at communities to see if there has been an effect on herbicides.

Initial data that is coming in indicates there has not been any effect of this integrated vegetation management on the ground beetle community.

Philip Charlton: Well, that’s going to be interesting to see in years to come.

Industry Funding Science

Carolyn Mahan: This research is funded by industry and there are particular objectives that industry has: what management approaches work best, and can they be compatible with biodiversity? But I also want to make it clear that industry, through their funding, is supporting pure science. We are finding really interesting information about distribution records in species of beetles and native bees that we did not know about.

We’re finding some interesting even results in some of the honeybees we’ve been collecting. Honeybees are not native to North America, but we still collect them on our study sites and we’re noticing some interesting anatomical differences in honeybees across the state. Even though that’s not the objective of this research, some very good pure science is coming out of our results and we’re really grateful for that.

For More Information

Philip Charlton: You have a great website where people can see summaries.

Carolyn Mahan: Yes, Transmission Line Ecology – Pennsylvania State. Transmission Line Ecology (

All our peer-reviewed publications are there and summaries of the work that we have done in the past is there. It’s where we put all our information. Very recently, I have been asked to expand our work into gas and oil rights-of-way which are managed differently than transmission lines for electricity.

We’re going to be initiating a project this summer with Shell on pipeline rights-of-way down by Pittsburgh. They are permitting us to set it up as a replica of State Game Lands 33 where we’ll take two miles of gas transmission rights-of-way divided up into different treatments and look at wildlife responses to those treatments.

Philip Charlton: Carolyn, are you willing to have people interested in your research or replicating your research reach out to you directly?

Carolyn Mahan: That would be great. On my website is my email. It’s publicly available if, if you just type in Carolyn Mahan, Penn State, you’ll find my email address:

Yes, people may reach out to me if they have specific questions. They may have questions about how to get a research project like this started. I also have faculty research colleagues around the country who are doing similar work. Some of their projects are just getting started, but I can also connect industry with researchers in other parts of the country if people are interested. People should not be shy about reaching out to me directly.

Philip Charlton: Carolyn, we want to thank you for your time. Very much appreciate it. Excited to see you again.

Carolyn Mahan: Oh, you too, Phil. Thank you very much.

Philip Charlton: That’s it for this episode of the Trees & Lines podcast, brought to you by Iapetus Infrastructure Services. If you like the show, please give us five stars on Apple or Spotify. If you have any questions or comments on any of our episodes, or ideas for topics or guests in the future, we’d love to hear from you.

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