Hillary Rosner is a contributing editor at BioGraphic. Her work has appeared in National Geographic and The New York Times.
Nonhuman species are facing a loss of connectivity that threatens their daily and seasonal movements.
To get from his house on the eastern side of the St. Lawrence River to his lab at Montreal’s McGill University on the flanks of the city’s namesake Mount Royal, Andrew Gonzalez has an easy commute. He takes a subway line that runs beneath the river, and then he walks or bikes from the station to the university. Sometimes, though, during the roughly 30-minute trip, he imagines what it might be like for another species to travel through this environment. Could a rabbit make the journey? A salamander? A deer?
Gonzalez thinks a lot about this sort of thing. An ecologist who studies the causes of biodiversity loss and how to prevent them, he has spent much of his career researching landscape connectivity—the degree to which animals are able to move within and between patches of habitat. Every species has a daily and seasonal pattern of movement, and distinct methods of crisscrossing a landscape to find food, water, shelter, and mates. But the myriad ways humans have sliced up, paved over, and otherwise radically reorganized Earth’s terrain impact species’ ability to get where they need to go to survive. Now, climate change is raising the stakes while throwing up new obstacles: Some species will need to migrate increasingly long distances to find suitable homes. One recent study found that in the United States, only 41 percent of existing “natural” areas are sufficiently connected to enable species to follow the environmental conditions they need.
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Back in the 1600s, what is now the urban metropolis of Montreal was a vast forest teeming with wildlife—including deer, moose, and beaver—whose presence was partly what enabled humans to thrive there. Today, though, few nonhuman species can cross—much less inhabit—this concrete island. Even far outside the city itself, forests and wetlands are giving way to suburban sprawl. The same is true in fast-growing cities around the world.
Gonzalez, who is tall and reedy and speaks with an accent from his native England, has spent the better part of a decade studying how his Canadian home appears from the viewpoint of other animals. Since 2011, he and members of his McGill lab have been assembling maps of “how each creature perceives the landscape”—which patches of land a bear, a nuthatch, a marten, or a frog can and cannot use.
Gonzalez, like most ecologists, believes keeping landscapes connected, and reconnecting isolated fragments, is crucial to safeguarding the planet’s biodiversity. Over the past few decades, a “connectivity” movement has been building momentum, slowly and quietly. The most audacious and high-profile North American project is the 25-year-old Yellowstone to Yukon Conservation Initiative, or Y2Y, an effort to protect the ecological health of a vast, rugged slice of the United States and Canada. In Europe, Natura 2000 is a network of protected areas stretching across roughly 18 percent of the EU.
The movement is beginning to gain the attention of lawmakers, too. A group of six northeastern U.S. governors and five eastern Canadian premiers recently signed a resolution recognizing the importance of landscape connectivity. This fall, a working group will meet to discuss how to prevent further forest fragmentation on a regional scale.
But while many efforts to link natural areas and create “corridors” for animal movement focus on large swaths of land, and the large mammals, such as bears and wolves, that use them, Gonzalez is concerned about areas more densely populated by humans—cities, suburbs, exurban expanses of advancing asphalt. He argues that protecting and restoring linked areas of green space, around and even within cities such as Montreal, is key to saving species from extinction, to enhancing the quality of urban life for humans, and to improving our understanding of how the natural world is shifting around us.
In an effort to move connectivity to the core of urban and regional land-use planning, his lab has built a computer model that uses data on species movement, climate change, and future patterns of development to show which areas are most crucial to conserve or restore.
As a steady spring rain fell outside a café near McGill, Gonzalez sipped a cappuccino and opened his laptop to a map of the St. Lawrence Lowlands, a network of forested areas surrounding Montreal, between the Appalachian and Laurentian mountain ranges. The map was colored in varying shades of gray, with a series of red and yellow splotches, some of which formed a band to the city’s northeast. The colored patches on this particular map represented the most important habitat for the ovenbird (Seiurus aurocapilla)—a migratory warbler that breeds in eastern North America and spends winters in Central America and as far south as Venezuela.
Researchers at McGill University are using computer models to identify critical habitats within the St. Lawrence Lowlands for each of 14 species, based on the habitat requirements of those species, and the connectivity of the habitats. This map indicates patches of habitat the scientists consider high priority for the conservation of a small songbird called the ovenbird.
Ovenbirds eat insects, which they typically find by rustling through piles of leaves on the forest floor. That type of “leaf litter” builds up over time and is more plentiful in older forests with larger trees. “There’s a very clear corridor to the northeast of the city—large woodlots, pristine forests, biosphere reserves,” Gonzalez says. Those areas are the ones that glow red on the map; even if it’s not contiguous forest, it’s a region of stepping-stone patches, farthest from the city’s suburban development, whose conservation is crucial to ovenbird survival.
Gonzalez’s model makes maps like this for each of 14 species, selected to represent a range of habitat and movement requirements. The American marten (Martes americana), for example, requires conifer forests, rather than deciduous forests—very different than the ovenbird and several other animals in the group. The 14 species are intended to represent an “envelope of diversity” that captures most, if not all, of the region’s vertebrate species.
The model considers a range of different future scenarios for climate and land-use change, and then ranks the importance of every forest patch to the region’s overall connectedness for all the species. It divides the landscape into pixels, each one representing a 30-meter by 30-meter area. Using a concept known as “between-ness,” the model evaluates how central any given pixel is to a larger network. In this case, the model calculates what happens for each species if a particular pixel—a tiny square of the landscape—were removed from its network. Each time a pixel is removed, an algorithm calculates the change in connectivity. Ultimately, the maps show color-coded priority areas for conservation.
For the ovenbird, the research shows that conserving just the most important 12 percent of pixels would actually protect 57 percent of the bird’s habitat. That’s a pretty good return on a relatively small conservation investment. Overall, for the 14 species represented in the model, protecting 17 percent of the most essential existing forest would maintain nearly three-quarters of the region’s connectivity. In other words, a little bit of foresight and conservation planning can go a long way.
Without any action to protect or reconnect these areas, though, by 2050 the forest cover will have shrunk by another 12 percent, says Gonzalez, with fewer, smaller, less-connected patches of habitat. By that point, it becomes much more difficult to undo development and protect the species occupying the scant forests that remain.
Back in the 1960s, biologists E.O. Wilson and Robert MacArthur developed the theory of island biogeography, a way to explain the distribution of species around the world. The theory also explained why splintered habitats tended to have higher extinction rates than those left intact. When you carve up an ecosystem with roads and farms and industrial areas, leaving behind disconnected fragments of nature, those fragments function like islands, leaving populations of animals and plants there marooned and vulnerable to everything from disease to localized environmental disasters to inbreeding.
Since the 1970s, research has repeatedly demonstrated that habitat fragmentation does in fact lead to huge losses of biodiversity. Beginning with a study in the Brazilian Amazon in the late ’70s, Thomas Lovejoy and a team of scientists set out to answer a question known as “SLOSS,” which stands for “single large or several small”—a debate about whether it’s better to protect a few giant chunks of land or many smaller patches. Over the years, their research has shown that there is a direct relationship between the size of a reserve and the long-term stability of species there, and that areas at the edge of forests are most susceptible to ecological damage.
The more fragments you have, the more edges there will be. In a paper published in 2015, a group of scientists, Gonzalez among them, looked at the effects of habitat fragmentation on ecosystems around the globe. They concluded that 70 percent of the forest that remains is within a kilometer of the forest’s edge—the most vulnerable region. “These findings indicate an urgent need for conservation and restoration measures to improve landscape connectivity,” they wrote.
But despite the bad news, there’s at least a sliver of hope. Evidence is mounting that it’s possible to recreate links. The Brazil study also demonstrated that secondary forests taking root on abandoned ranchland can serve as corridors for wildlife—everything from ants to monkeys to big cats. Given half a chance, nature can, it seems, bounce back.
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As an undergrad at the University of Nottingham, Gonzalez took an ecology course and became “intrigued by the idea that one of the things you can see humans doing from space is fragmenting landscapes.” He was fascinated by both the theoretical and mathematical approaches you could use to study habitat fragmentation, and also by the pressing, real-world challenge of solving the problem. It was the early 1990s and, according to Gonzalez, not much research had been devoted to understanding “how entire communities and ecosystems might undergo cascades of extinctions,” and what would happen to those ecosystems as a result. He began with an honors thesis project, studying not city-size landscapes but far smaller ecosystems: patches of moss.
“Lumps of moss form little islands,” he explains, still enthusiastic about these elfin ecosystems more than two decades later. “And inside is a plethora of microarthropods”—tiny invertebrates, sometimes hundreds of different species of them. “The moss patches are like a miniature rain forest; they’re fascinating.” For several months, Gonzalez tested island biogeography theory, studying whether bigger islands of mosses contained more species, and if you cut islands in half whether the loss of connectivity triggered extinctions. It was the SLOSS question, writ tiny. He was hooked.
But he also knew he wanted to apply ecology to help protect the planet’s biodiversity, not just study moss in a lab. So he went to his advisor and told him, “‘I want to save the world; I want to reverse forest fragmentation,’” Gonzalez recalls. “And he goes, ‘Here’s my advice. Go and train to be the best possible scientist that you can, and then come back to the problem of saving the world. Then you’ll be ready.’ At the time,” Gonzalez says, “I thought that was a bit frustrating because I wasn’t going to be able to get to the problem-solving for quite a long time.”
Still, he complied. He continued his moss experiments as a Ph.D. student under British ecologist John Lawton, who, Gonzalez says, “was also fascinated by this idea of patchiness, connectivity, fragmentation, and how could we better predict what will happen in the future if we had the right theory.”
Using the mosses, Gonzalez tested whether linking the patches with corridors could slow extinction. He built corridors between some patches, left some isolated, and broke the corridors between others. He found that the corridors did indeed stave off species’ demise.
Eventually, he took a job at McGill, where he continued to study biodiversity declines, this time in the taiga of Canada’s boreal forest. There, he warmed the ground’s mossy layer to see if it altered how insects and other arthropods moved through the environment. The idea was to understand how climate change might intersect with fragmentation to drive extinctions. And then one day in 2009, his phone rang.
An employee with the Quebec Department of Sustainable Development, Environment, and Parks was on the line. “He said, ‘I’ve heard about your work on corridors. We’re worried about urban sprawl; climate change is coming; and we’re losing our forests. Could you have a think about using your research to design corridors for Montreal?’” It was the opportunity Gonzalez had been preparing for.
The region’s population was growing quickly, and was expected to add a million more people by 2050. The city wanted to explore building a greenbelt, based on the most ecologically sound design. Climate change’s impacts were already becoming visible—not least in the rapid spread of Lyme disease, in part because the disease-carrying tick can now survive over the winter here. Inspired by the chance to do real conservation, Gonzalez set about building computer models to help city planners decide which areas were most important to protect or restore.
Working with the David Suzuki Foundation, a Vancouver-based environmental nonprofit, he helped answer questions like how best to reduce urban heat islands while also maintaining biodiversity corridors. Jean-Patrick Toussaint, who oversaw the Foundation’s greenbelt work at the time, used Gonzalez’s model to assess a proposed development west of Montreal. The project was being sold as environmentally friendly, recalls Toussaint, but in fact it threatened a number of important, and rare, plants and animals that lived there. The model showed that removing the habitat would cause losses in connectivity, which would ultimately have impacts on a much larger scale. “That sort of work really raised eyebrows,” Toussaint says. “It led to a discussion about how to integrate Andy’s science with the planning tools of city officials at the highest level.”
Since then, though, Montreal’s greenbelt effort has lagged, and sprawl continues. Ecology, as scientifically compelling as it may be, still wages an uphill fight against development’s money and momentum. But now that word of the mapping tool has begun to spread, interest in its potential is growing at the grassroots level, where so much of the work on sustainable cities is happening.
In a low-rise, ultra-green office building in Montreal’s arts district, a sustainability group funded by both the city and the province is working to create a neighborhood greenbelt one tree at a time. Projet ILEAU (Interventions Locales en Environnement et Aménagement Urbain) is trying to turn a heavily industrialized, heavily asphalted, disproportionately poor area called Anjou into a model for how to build a green-and-blue-belt (incorporating both greenways and waterways) on a scale as localized as the plants in your backyard.
Gonzalez’s maps provide an overarching framework for Anjou’s renewal effort—which includes an attempt to minimize urban heat islands. “Without the idea of connectivity, we wouldn’t have a vision for our project,” says Michelle Craig, ILEAU’s project manager for the environment. Having the science to back up their effort helps ILEAU’s staff be more convincing when talking to local officials. The group is working with residents on tasks like ripping out asphalt “yards” and replacing them with plants, calling on citizens to become bûcherons de l’asphalte—asphalt lumberjacks—“replacing the gray concrete of cities with the colors of nature.”
They are also assembling a small green corridor between a school and a church, linking existing parks, and opening to the public a cordoned-off, 247-acre forest called the Bois D’Anjou. “The idea is that slowly there will be corridors,” Craig says. “It’s definitely tough. You have to start small. Long-term, this is what we want people to dream about.”
ILEAU envisions not just connected parks but corridors, for wildlife and humans, constructed from existing infrastructure—the space beneath power lines, for instance. Much like New York’s High Line, built on abandoned elevated train tracks, or Los Angeles’s ongoing effort to transform its concrete-encased river into a thriving ecosystem and a blue-and-green corridor for city residents, ILEAU is trying to turn blighted urban infrastructure into assets.
Gonzalez is tapping into the same zeitgeist. One project underway involves working with a new overground Montreal rail line that will soon be built, trying to make it “a net positive for biodiversity” by viewing the area beneath and around it as a green corridor. That idea dovetails with a nascent campaign in the United States to use power-line rights-of-way—long derided for slicing across forests—as migration corridors, particularly for some birds, bees, and butterflies. (The Right-of-Way Stewardship Council even issues standards for utilities to maintain the vegetation under their power lines; seven utilities have been certified under the program.)
The McGill team also hopes its work might help prevent locally at-risk species from disappearing. They’ve identified 10 sites around Montreal with ideal habitat for the western chorus frog (Pseudacris triseriata) or rainette faux-grillon (literally, “fake-cricket frog" in French)—a species that, while common across much of Canada and the United States, is endangered around Montreal due to urbanization. The frog has very specific habitat needs: young forests, wetlands, and high humidity.
“It’s quite possible that it is a living fossil, that the frog will go regionally extinct,” Gonzalez says. But if he can show that areas where the frog and other rare or threatened species can persist are also crucial nodes in the connectivity network more broadly, then the local chorus frogs just might have a chance.
Saving a species that’s only regionally at risk may seem like small potatoes in the overall conservation game. Surely it would make more sense to focus on creatures that might vanish entirely. At a local level, though, losing even a single species can have outsize impacts on ecosystem health. In places where only small patches of forest remain, “seemingly minor decisions can have a big effect,” Gonzalez says.
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Of course, connectivity presents its own set of challenges in a world where all kinds of species are on the move. If you build a bridge, you can’t really control who—or what—crosses it. Since the 1980s, some scientists have been warning that linking landscapes via corridors opens the door to invasive species and disease.
In the case of Quebec, Lyme disease illustrates the problem. The disease is carried by ticks, which are carried by mice. “It’s a climate story but also a connectivity story,” Gonzalez says. Preliminary research by a McGill colleague suggests the mice are using rail tunnels to cross the river. Much like the humans that rely on underground corridors, the white-footed mice, and their piggybacking ticks, are migrating via the paths available to them.
In our increasingly fragmented world, the benefits of maintaining or recreating the natural connections among ecosystems clearly far outweigh the costs. But the mouse story is a good reminder of the need to consider all different kinds of corridors, and to think about how those can shift over time. Before the subway was built, Gonzalez’s commute might have involved crossing the St. Lawrence River by boat or perhaps, in the winter, on skates across the ice. (That’s no longer possible though; as the climate has warmed, the river no longer freezes.)
Standing atop Mount Royal in the pouring rain, his shoes soaked from the long walk up a series of steep wooden staircases, Gonzalez looked west across the St. Lawrence River and into the fog hanging over the region. Through the mist, he pointed out small remnant patches of woods and even tree-lined streets whose canopies of green serve as corridors for all manner of birds and insects.
His goal, he said, is to build his connectivity models into something people can access and use in real-time. Just as you might now pull up a website showing the local weather forecast, he envisions a tool where everyone could see how the connectivity of their local landscape is changing. “What’s the heat island prediction? What’s the runoff? Are you likely to see that cardinal in your garden this year, because that forest patch has been cut down to build the hospital?”
Even through the fog, it was possible to see down to the old port of Montreal, where French colonists landed hundreds of years ago to find woodlands filled with moose, deer, bear, beavers, porcupines, and scores of other creatures. Today, a museum sits on the waterfront spot where the city was founded in 1642. Visitors there can walk on Plexiglas flooring above the ruins of the original city foundations, as a wall-size screen displays dappled sunlight penetrating the expansive forest that still stood. From space, one would have seen a vast, unbroken canopy.
The museum also houses a historic tunnel. City engineers built it in the 1830s to channel a small tributary of the St. Lawrence, called the Little River, underground. Early European settlers once used the Little River as an open sewer, and by the late 1700s, the stream was so polluted it was making people sick—a corridor for disease. Today, that water travels through a modernized sewer network, and the sealed-off tunnel functions only as a museum exhibit. It’s a testament to shifting corridors, and to the ways in which humans are constantly altering nature’s paths, for better or for worse.