paved trail

Whenever the issue of paving Bolin Creek comes up, the Friends of Bolin Creek (FOBC) flood the zone with unfounded environmental concerns about paving alongside Bolin Creek.

Of course, there are always trade-offs with projects, but paving a 10-foot-wide path along an existing 30-foot-wide sewage easement seems like a no brainer: It uses an existing corridor devoid of trees, will make it easier for people to get to school, provides a safe and comfortable mechanism for people to enjoy nature, and connects Carrboro with the already existing (and paved!) Bolin Creek Trail in Chapel Hill. (To learn more visit Carrboro Linear Parks Project and sign up for their mailing list!)

Bolin Creek missing greenway

In fact, there are many examples of sewage easements across the country that have been turned into paved paths next to streams, including the Bolin Creek in Chapel Hill, Riverwalk in Hillsborough, and paths in Durham and Raleigh. And there is evidence that placing small paved paths next to streams actually helps erosion — right now, people walk all over the place to avoid puddles, and putting down a paved path keeps them in one place.

I reached out to Paul Taillie, a wildlife ecologist and professor at UNC, to talk through the issues that FOBC has raised.

Q: Thanks for taking the time to chat with me, Paul. What do you do?

A: I’m an Assistant Professor at UNC in the Geography Department where I study the effects of urbanization, invasive species, and climate change on the distribution, habitat use, and movement of animals.

Q: Before we begin, can you tell me if you’ve ever been paid by Friends of Bolin Creek or have a backyard facing the Bolin Creek? I ask because some of the environmental experts they frequently cite either live directly next to the creek or were paid for their work.

A: Nope. I used to live very close to the section of creek in question, and during those years I spent lots of time there looking for animals. The proximity to the trail was probably my favorite thing about that house.

Q: Cool. Can you tell me why greenways are important?

A: In general, greenways serve as critical elements of urban infrastructure. In addition to providing space for recreation and transportation, they also provide accessible opportunities for interaction with nature, which is increasingly in short supply for many urban communities. Some of my colleagues joke that every single research article about urban ecology these days starts with the same sentence: “For the first time ever, most of the world’s population lives in cities.” To me, this illustrates that providing opportunities to engage with the natural world in cities is more important than ever.

Regarding animals specifically, even narrow greenways can support a surprising richness of species; however, some previous research has found that a forested corridor 100 m wide or more can support interior forest birds like wood thrush, hairy woodpecker, and Acadian flycatcher. Beyond supporting a diversity of plants and animals themselves, greenways serve as important connections and corridors for movement between other urban forest fragments.

Greenways are often established along creeks and rivers, which can help to limit development along these waterways. These riparian (i.e. streamside/riverside) corridors play an important role in buffering waterways against pollution and other impacts that would otherwise degrade water quality. It’s quite common to see semi-aquatic species like turtles and amphibians crossing greenways as they access adjacent waterways and forest.

Q: Even in locations where there’s already stuff built up, like the single family homes we see all around Bolin Forest?

A: Absolutely! Even when single family homes are on large lots with huge trees, like many neighborhoods in Chapel Hill, there are things animals are looking for that they don’t typically find in our yards. Things like snags, which is a term for standing dead trees. Homeowners typically remove trees as soon as they die because of the risk they can pose to property. Similarly, downed logs and other coarse woody debris provide important cover for lots of ground-dwelling animals, but these are typically absent from our yards. So greenways and other urban forests play an important role in providing habitat for animals even when there are lots of trees around otherwise.

Q: I see a lot of Friends of Bolin Creek citing birds that they see in the unpaved Bolin Creek area as a reason that the creek should remain unpaved. But I also see that eBird counts show the same birds in the same numbers on the paved sections of Bolin Creek. So I’m curious: How are greenway characteristics related to bird habitat quality?

A: Alright, so there’s a few things going on here, so let’s address them one by one.

First, it’s important to note that when we look at raw counts of animals, whether from eBird or elsewhere, we’re going to find more birds if we spend more time looking. Thus, it can be tough to disentangle whether there are truly more birds, or if more were simply detected. What this means is that we should really account for differences in survey effort (i.e. time spent birding) if we’re going to make meaningful inferences about differences in bird abundance between two places.

Ok, so researchers have done this. Raleigh is well known for its extensive greenway system, making it a great place to investigate how greenway characteristics might be related to animal abundance and community composition. One of the key take-home messages from this work is that wider forested corridors increase bird diversity. Along stretches of greenway with narrow strips of forest or vegetation, urban-adapted species like mourning dove, house wren, and house finch are most abundant. But when a greenway is contained within a broader corridor of forest, specifically wider that 100 m, the bird community more closely resembles that which you’d expect to find in a forest outside of town.

In regards to the particular stretch of trail in question, the “forested corridor”  is huge because its adjacent to Carolina North Forest. As a result, it is some of the best birding in Carrboro. Hooded warblers, wood thrush, northern parula, and other species associated with riparian forests are pretty easy to find here. In addition, scarlet tanagers and blue-headed vireos can be found breeding in the upland pine forests, which is notable given that these mountain species are at the edge of their breeding range here in Orange County.

As far as I can tell, not even the most sensitive interior forest species would be impacted by paving the trail. Granted, few if any studies of forest bird habitat quality in urban environments have identified the extent of pavement as a driver of bird habitat use. However, there are several other spots in the triangle where you can easily find wood thrush, barred owl, and pileated woodpecker without leaving pavement.

So the amount of forest is more important than whether or not the trail is paved?

A: Yes, the width of the forested corridor adjacent to the trail is way more important to birds and other wildlife than the characteristics of the trail itself (e.g. paved or not). Sure, pavement and extent of impervious surface are often negatively correlated with forest bird diversity and abundance in cities; however, building a paved trail through a forest has a trivial contribution to the extent of existing pavement throughout town.

The other key factor affecting forest birds and wildlife in urban environments is invasive species, which are often more problematic in urban areas when compared to forests in less-developed areas. Most notably, cats are one of the biggest threats to wildlife in America where they kill billions of birds and mammals every year (Keep your cats inside, I do!). Aside from invasive predators, invasive plants like chinese privet, japanese stilt-grass, and autumn olive readily outcompete native shrubs and forbs, which decreases diversity. Granted, some birds do consume the fruits of these invasive plants, but these foods are only available during a certain time of year. In contrast, a forest with a diversity of native shrubs provides essential food and cover resources throughout the calendar year. Similarly, arthropod food resources are more diverse and spread more evenly across different times of year in urban forests of eastern North America that have diverse, intact native plant communities compared to those dominated by invasive species.

Q: But controlling invasive species is notoriously challenging, right?

A: If you asked me five years ago about the feasibility of controlling invasive privet along Chapel Hill’s greenways, I would have said forget it, too hard. In fact, that actually happened. Jeanette Bench and Michael Everhart had a radical vision for transforming the Booker Creek Greenway from a tangle of low quality urban forest dominated by privet, to a haven for native plants and animals, as well as people. All types of people. Their first step in this vision was to eradicate privet, which in my experience, is a near impossible task, even for organized land management agencies armed with drip torches, chainsaws, and herbicides. Jeanette and Mike asked me what I thought about achieving this vision with an army of untrained volunteers. I was skeptical.

Amazingly, they proved me very wrong. For several years they have coordinated various partners including the Town of Chapel Hill, New Hope Audubon Society, and the North Carolina Botanical Garden. And with the help of all sorts of volunteers from youth groups to retirees, they have transformed much of the Booker Creek Greenway,

Thus, there exists a great deal of experience and momentum to make meaningful changes to the Chapel Hill/Carrboro urban ecosystems that benefit native wildlife and these changes would more than compensate for the effects of the paved connection. Apologies if this discussion of invasive species took the conservation in an unintended direction, we can get back to talking about paving the trail.

Q: So it sounds like you’re for paving the corridor. I’m curious what you think of the arguments against paving made by a stream ecologist who lives right next to Bolin Creek and who serves on the FOBC board. They frequently cite his letter, which says riparian buffer zones along creeks aren’t great for greenways and that paved roads have profound effects on ecosystems. Your thoughts? 

The author (Dr. Paul, not to be confused with myself, a doctor named Paul) makes a lot of great points! I would certainly agree that riparian ecosystems provide a number of important hydrological and ecological services, making them valuable environmental assets. As a result, their development should be avoided whenever possible.

With regard to animals specifically, I also agree with Dr. Paul that greenways aren’t teeming with wildlife “because of the pavement.” This observation is likely an artifact of the fact that more people have easier access to these areas with paved trails, and so find more animals. There could certainly be negative consequences of paving the trail, particularly for salamanders and other fossorial animals, but I think these consequences would be trivial, given that the vast majority of forest would remain unaffected. For birds and mammals, I think it’s extremely unlikely that there would be any noticeable impact from this project.

More broadly, I simply don’t think many of Dr. Paul’s points are relevant to this discussion of paving the existing trail. We’re talking about converting an existing, heavily-trafficked trail that exists next to a highly altered urban stream whose watershed consists of A LOT of impervious surface. Paving the section of trail in question would not involve razing the forest or grading a new road bed. In my view, it is unlikely that the proposed project would have a noticeable effect on wildlife. Though I’m not a hydrologist, I would even be surprised if paving the trail had a measurable impact on water flows or stream morphology. (Ed note: We’ve talked to a hydrologist and spoiler alert: no measurable impact.)

While the potential impacts of this project to wildlife are minimal, the benefits to our community are great. Aside from the aesthetic, health, and climate benefits that result from a more walkable/bikeable town, paved greenways provide access to nature for people who might not find it elsewhere. I experience this all the time because I want to go look for birds, but my two young kids get tired of walking after about 20 seconds. Greenways like the Bolin Creek Trail have been such a gift for me because my kids can sit in the stroller instead of up on my shoulder pulling on my binocular strap. Sure, there are also days when I can leave them at home and want to get away from the greenway traffic, but Carolina North has plenty of opportunity for that, which would be unaffected by the paving of the connection.

Melody Kramer

Melody Kramer (@mkramer) serves on the OWASA board and lives in Carrboro with her family. By day, she leads communications for a large academic research center and recently obtained her MLIS degree focusing...