An aerial view of a green bridge in Girona, Spain, where wildlife can safely cross the main road. Photography: Artur Debat/Getty
The human road has completely fragmented the wildlife world, but the project to reconnect the fragments is in our hands
An aerial view of a green bridge in Girona, Spain, where wildlife can safely cross the main road. Photography: Artur Debat/Getty
Emeritus Professor of Ecology at Griffith University in Queensland, Australia. His books include "Birds on My Table: Why We Feed Wild Birds and Its Importance" (2018) and "Clouded Leopard in the Middle of the Road" (coming soon in 2022). He lives in Brisbane.
As Harvard landscape ecologist Richard TT Forman described, it is almost certain that you have recently interacted closely with an invisible giant. Others call roads "the most destructive factor in the process of habitat fragmentation" and claim that "there are very few powers that are more influential in changing the planet than transportation." However, you may not even notice. A broad feature that can capture the world but is actually invisible: a huge transportation infrastructure network-all railways, canals, and most importantly roads. Roads are everywhere, forming an almost unimaginable complex system, an endless, expanding, and interconnected grid that promotes the flow and exchange of people and goods in vast areas. This huge structure may be the greatest cultural artwork in history, and it is a necessary and prerequisite for human development. For us, roads are essential connectors, connecting places and purposes. But, almost everywhere, these networks have been imposed on environments that people have overlooked.
Despite its extraordinary scale, this huge, inevitable, and indispensable network has been largely ignored. When we shuttle between the places where we live, shop, study, and entertain, we are unlikely to think about the road we travel. (Of course, the traffic situation we encountered is another matter.) It is even less possible for us to regard the road we are driving on as consisting of all the roads spread over the region and the entire continent.
If we imagine a road, it is probably the shortest distance travel from A to B, as shown by the map application on the smartphone. What is even more difficult to imagine is the interconnected road network, a literal network, sometimes densely gridded in places where many people live, and sometimes forming scattered ribbon-like structures around sparsely populated difficult terrain. Of course, this is not only the most effective connection we should consider to people, but also the resulting fragmentation of the landscape into land bounded by roads in all directions. These parts may be urban blocks, farms, or national parks, but to some extent, they are all restricted by the surrounding roads and traffic. Unsurprisingly, there is a strong and obvious relationship between population density and road density. This is most obvious in small countries with large populations. For example, the Netherlands is compact and crowded, with a road density of 1.55 kilometers (0.96 miles) per square kilometer. However, even in a significantly spacious country like the continental United States, there are few places that are only a few miles away from paved roads.
Why is this important? Imagine any large animal, perhaps a deer or a wolf, that needs to travel for any typical but compelling reason: looking for food, finding a mate, and migrating regularly. No matter where it lives or where it moves, it will be on the road sooner or later. What happens next depends on many different factors. It may take this route regularly and is very familiar with sudden changes in the landscape. Or it may have never encountered a road before. It may even be attracted to graze on the side of the road, taste edible garbage, or remove dead animals found nearby. On the other hand, traffic noise or lights can be disturbing, so that the animals will stay as far away as possible. If there is no vehicle, the animal may cross or enter the traffic flow directly inexplicably. Despite the risks, it may have enough power to cross, or after learning to judge the safe interval between moving vehicles, it may delay crossing until the quietest time at night. All these reactions happen almost every day.
Crossing roads is usually dangerous for wild animals, especially for slow-moving ground dwellers. Collisions with vehicles almost always result in death or serious injury to animals, and the numbers involved are almost unbelievable. For example, about 1 million people are killed on American roads every day. Throughout North America, the cumulative scale of all these road killings now exceeds hunting and is the main cause of death for larger species. It is now regarded by researchers as an "evolutionary fiction threat." Although certain types of mammals, such as deer (more conspicuous) dominate the statistics, the number of smaller, less obvious groups, such as birds and amphibians, is huge.
Of course, not every road is dangerous. Some nights have little or no traffic. Certain species have learned to avoid vehicles and cross when safe. Even the shockingly high number of road deaths does not mean that a certain species or local population is threatened. There are many visible road deaths that may just indicate the abundance of species in the area. Of course, a large number of white-tailed deer in North America or roe deer in Europe died as a result of collisions with vehicles, and the impact on their numbers is minimal. However, there is strong evidence that collisions with vehicles can push species to the brink of extinction. Notoriously, in the 1980s, approximately 10% of the Florida panther population was killed every year. In Tasmania, a simple road upgrade led to the extinction of a rare marsupial carnivore.
Although seeing animal carcasses on the roadside is disturbing, other effects may be far more important. For many species, traffic is not a problem: the roads and related spaces are important. In extreme cases, some animals-such as small birds or rodents that inhabit the forest-will not even cross a small road, whether there are cars or not. For these species, the gap may be a complete obstacle to their movement. This so-called "barrier effect" is one of the most important recent discoveries made by scientists studying roads.
These insights add a new and shocking dimension to our understanding of the ways in which habitat destruction affects biodiversity. The cumulative effect is that the once continuous natural landscape is ruthlessly subdivided piece by piece and divided into smaller and smaller patches. The most obvious is that the resulting landscape becomes a series of discrete islands, each of which is isolated from each other by a completely different and usually hostile environment around it.
The challenge is daunting and incredibly complex, but the hybrid field of roads and landscape ecology that is just getting started offers realistic hope: "Perhaps just right," Foreman in "Road Ecology" (2002) Wrote, "A solution seems to be in front of us. The basic knowledge includes transportation, hydrology, wildlife biology, plant ecology, population ecology, soil science, water chemistry, aquatic biology, and fisheries. Combining these fields should lead to scientific expansion, which contains useful applications.
These words were written 20 years ago and have proven to have extraordinary foresight. Of course, roads continue to decompose and isolate, bringing degradation to some of the most remote places on the planet. But in Borneo, Brazil, India, and Idaho, and other diverse places, unexpected allies are uniting to find ways to reconnect long-cut fragments and provide safe passage for various creatures.
It was early morning, and a ghostly mist rose from a thin meadow. It is cool, moist, and clear. A frog called for an emergency from somewhere above and suddenly broke the silence. On the edge of the dark forest, a pair of roe deer, gray figures, quickly raised their heads, but soon continued to eat grass. A lone bat passed by, and then returned peacefully.
We slowly crossed the wet grassland on the border between Belgium and the Netherlands, where non-stop cars and trucks drove along the large highway (E34/A67) connecting Eindhoven in the south of the Netherlands and Antwerp in Flanders, sending out continuous The buzzing sound. Although there is no clear international border, the region is one of the most ecologically fragmented in the world, the result of thousands of years of intensive agriculture, logging, and countless conflicts (including the catastrophic effects of the two world wars). In this special place, many important species and ecosystems are very susceptible to human disturbance, and some are on the verge of extinction, and there are still promising numbers.
This may be a place as perfect as any place where the uneasy embrace between human behavior and the natural world can be firmly considered and redesigned. When we walked slowly along a stable slope onto the broad and flat grass and exposed sandy substrate, the rising sun had dissipated most of the fog. I thought that these vacant lots were bare for the time being, and shrubs and trees would eventually be planted, but I soon learned that this barren appearance was deliberate. One of the most important species found here, the smooth snake, prefers open sandy habitats. These long, bare areas are managed intensively to maintain this state; snakes thrive under the exposed sky. On the broad slopes to the south, the sand belt transitions to eventually become a dry acidophilic oak forest, suitable for hummingbirds and black woodpeckers. Finally, a strange grated doorway hidden in a steep ravine points to the entrance of a damp underground concrete labyrinth designed for another important local species, Geoffroy's bat.
From Sweden to Romania, animals from salamanders to revived brown bears are safely crossing busy roads
We continued on, past rows of exposed and inverted tree roots and broken trunks (a habitat for reptiles and small mammals), and then walked down steeply, leaving traces on the sand with our feet. A series of small reservoirs were installed at the bottom of the slope to collect runoff and provide breeding grounds for amphibians. As we walked around the corner of the long wing, an overpass designed for wild animals-known as an "ecoduct" in Europe-came into view. A huge bridge-like structure extends above the road and far beyond the edge of the highway, providing ample space on both sides of the road. The shape of the huge curved wings circling on both sides is inspired by the undulating patterns of sand snakes on the loose substrate.
From the side of the road, it is finally possible to see the grandeur and hugeness of this structure. Known as Ecoduct Kempengrens (meaning "on the border of the open field"), this is an amazing building. It is 60 meters (65 yards) wide at the top and extends to 200 meters (220 yards) at the bottom of the wide slope. Right above the road, the weight of steel bars used only for earth bridges is 1,325 tons (1,460 US tons). It is one of the most complex and ecologically complete wildlife crossing structures ever designed. Many bats and more than 15 mammals have been detected using this structure.
In some respects, the most extraordinary achievement of this structure is the cooperation between people from jurisdictions on both sides of the border. Although the laws, funding, procurement and design processes of the Dutch and Flemish authorities are quite different, the relevant personnel believe that the goals are too important to allow simple bureaucratic obstacles to become obstacles.
This extraordinary structure is impressive, but it is only one part of the EU's comprehensive defragmentation project. Throughout Europe, on the road (and rail line) from northern Sweden to eastern Romania, animals from salamanders to resurgent brown bears are safely crossing busy roads. In each case, important consultation and cooperation are essential.
Although the highest-level authorities are also involved, the key driving force for such projects often comes from local community groups or citizens who unite to oppose the proposed road project. The spectacular wildlife overpass on Interstate I-90 in the Cascade Mountains in inland Seattle is one such example.
The Washington State Department of Transportation (WSDOT) finds itself facing a large number of well-informed groups filled with determined and experienced people who are eager to come up with other ways of thinking about upgrading through Cascades. WSDOT started the mandatory public consultation process with a plain “we are just building roads” and soon found itself at the end of a failed public relations campaign. It is commendable that the institution is willing to listen and learn. Opposition groups openly acknowledge that escalation is necessary—a clever disarmament strategy—but forcefully describes the major impact that will occur unless changes are made. Negotiation was difficult at first, but as many participants got to know each other, suspicion and hostility decreased. The result is a structure of inestimable value to land, people and animals, and an important symbol of where real cooperation can take us.
O Overpass is undoubtedly the most effective of all wildlife crossing structures. Their large size allows a wide variety of species to hybridize, especially if additional vegetation is included. Although these large buildings are traditionally built for large animals (elk, bears, deer, reindeer, kangaroos) and are usually similar to grassy mountains, for example, adding trees, bushes, or collecting water can attract a variety of Species. A well-studied, fully vegetation-covered overpass near Brisbane, Australia now has more amphibians and reptiles living on the building than in the surrounding forest.
A successful crossover structure does not need to be large or complex. The busiest passage for animal traffic is almost certainly the amphibian tunnel, which has been installed in many places to help amphibians move safely from the wintering site along the slope to the breeding pond. Every spring, hundreds of thousands of toads, frogs and salamanders use these small culverts. Locals often provide help. They will transport buckets of goods across the road and guide (human) traffic at key locations. These "frog tunnels" are simple and inexpensive to install, just slightly modified versions of the countless pipes and culverts under almost every road on the planet. Since the installation of these ubiquitous pipes was first started in the 1990s, countless organisms have been using these ubiquitous pipes. But there are some obvious limitations, such as being often filled with water (as expected), and of course the size.
Today, underground passages dedicated to wildlife can be seen everywhere and can accommodate species of various sizes, literally elephants (such as those built in Kenya and Malaysia about 10 years ago). As a version of the concrete box culvert, diversity can be increased to encourage wider animal use: along wall ledges or elevated on poles, sand, soil and even shade-tolerant moss, rocks, logs and piles Wood chips. All of this turned the cold, bare tunnel into a seemingly safer and less artificial passage. But only one thing: they are still long, dark places, completely different from anything that most species encounter in their natural environment.
There are some species that need another approach. If possible, it is understandable that those dedicated to living on the treetops are reluctant to descend to the ground. For larger animals, such as koalas or monkeys, a broken canopy means that climbing and walking are inevitable, but there are risks, especially if you have to cross the road. Now, there are many structures connecting the trees above roads all over the world. There are many rope ladders, which can help possums, squirrels, reptiles and possums to move safely to the tree on the other side. In India and Madagascar, slow loris, langurs and lemurs use simple and cheap bamboo bridges every day.
A set of diversified innovative cross structures is completely changing the way roads are designed and constructed
Other species avoid the ground by "flying"—actually gliding—from tree to tree. For example, flying squirrels, marsupial gliders and gliders can now traverse some narrow roads in the air, but any wider roads will become a serious challenge. In Australia, appropriately spaced "glide poles" allow sugar gliders and other species to cross major highways in a series of steps, rather than a huge gliding.
This diverse and innovative cross-structure kit is revolutionizing the way roads are designed and constructed. They provide real hope for the cut-off population and try to fragment the landscape everywhere. But let us also be realistic about the scale of this challenge. At the time of writing, it is estimated that another 25 million kilometers (15.5 million miles) of roads will be built in the next 30 years, most of which are planned for Central and South America and Africa.
In 2013-14, China launched two ambitious and large-scale initiatives: the “Belt and Road Initiative” (formerly known as the “Belt and Road”); and the 21st Century Maritime Silk Road. These interconnected projects envision a global transportation infrastructure network that spans most of the earth, effectively connecting China with the rest of the world. The scale of these plans—involving ports, railways, and extensive road projects—makes them by far the largest and most expensive infrastructure construction project in the world.
These and other large-scale transportation plans are being rolled out in many parts of the world, especially in poor countries in the tropics; usually, where political decisions are made in the capital, the impact of local infrastructure projects has little connection or consideration. The planning and construction standards set on paper usually bear little resemblance to what actually happens. Funding for ongoing maintenance is a key factor in the long-term operation of these roads, but it is rarely sufficient or simply disappears.
More worrying is the unplanned development of the area near the road. From local expansion of bushmeat hunting and opportunistic slash-and-burn cultivation to complex large-scale illegal timber smuggling, the impact of the new invasion can spread to neighboring forests in an almost organic, disease-like pattern. In Brazil, 95% of the tropical rainforest lost in the past ten years was within 5 kilometers (3 miles) of legal roads, which triggered the spread of "expanding illegal secondary and tertiary road cobwebs," according to road researcher William Lawrence and Irene Burgess Areia. The neat lines printed on a professionally produced glossy proposal may only be a small part of the actual affected area.
In 1998, the motivation to meet the challenge was so low that Forman and his co-author Lauren Alexander described road ecology as a "sleeping giant" waiting to be awakened. Three years later, we can say that this giant is now fully awake. Timely: There is a lot to do now.
Part of this article is adapted from Darryl Jones' "Clouded Leopard in the Road: New Thinking on Roads, Wild Animals, and Humans" (2022) by Darryl Jones published by Cornell University Press.
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