What is the most common form of human infrastructure in the world? It could be the fence though. Recent estimates indicate that the total length of all fences around the world is 10 times the total length of roads. If the fences of our planet are stretched to the end, they will probably bridge the distance from the earth to the sun several times.
On every continent, from cities to rural areas and from ancient on modern people sometimes built fences. But we know almost nothing about its ecological effects. Border fences are regularly in the news, but other fences are so ubiquitous that they disappear into the landscape and become rather a subject.
In a recently published study, our team tried to change this situation by presenting a set of findings, frameworks and questions that could form the basis of a new discipline: fencing ecology. By compiling studies from ecosystems around the world, our research shows that fences produce a complex range of ecological effects.
Some of them affect small-scale processes such as building cobwebs. Others have much broader effects, such as Accelerates the collapse of the Mara ecosystem in Kenya. Our findings reveal a world completely reorganized by a rapidly growing latticework of fences.
Connect the dots
If fences are strange for ecologists to study, keep in mind that until recently no one had thought much about how the roads affect the places around them. Then, in an explosion of research in the 1990s, scientists showed that roads – which have been part of human civilization for centuries – had narrow footprints but had tremendous environmental effects.
Roads can, for example destroy or fragment habitats on which wild species rely to survive. They can also promote air and water pollution and vehicle collisions with game. This work has a new scientific discipline, pathology, which offers unique insights into the staggering scope of humanity.
Our research team was interested in fencing by watching animals. In California, Kenya, China and Mongolia, we have all observed animals behaving strangely around fences – gazelles taking long detours around them, or predators that follow “highways” along fence lines.
We reviewed a large amount of academic literature in search of explanations. There were many studies on individual species, but each one told only a little on its own. Research has not yet linked the points between very diverse findings. By linking all of these studies together, we have discovered important new discoveries about our enclosed world.
Reconstruction of ecosystems
Perhaps the most striking pattern we found was that fences are rarely unequivocally good or bad for an ecosystem. Instead, they have a myriad of ecological effects that produce winners and losers, determining the rules of the ecosystems where they occur.
Even ‘good’ fences designed to protect endangered species or restore sensitive habitats can still ecosystems shatter and isolate. Fences built in Botswana to prevent disease transmission between game and livestock, for example stopped pulling wildebeest in their tracks, which produces ghostly images of injured and dead animals scattered along fencelines.
Closing an area to protect one species may injure or kill others, or create access paths for invader species.
One finding that we think is critical is that fences usually yield multiple losers for each winner. As a result, they can create ecological ‘no-man’s lands’ where only species and ecosystems with a narrow range of characteristics can survive and thrive.
Regions and continents change
Examples from around the world demonstrate the powerful and often unintended consequences of fencing. The boundary wall between America and Mexico – most of which fit our definition of a fence – is genetically isolated populations of large mammals such as large horned sheep, leading to declines in populations and genetic isolation. It even had surprising effects on birds, like iron-like pygmies, flying low on the ground.
Australia’s dingo fences, built to protect livestock from the iconic canines of the country, are one of the longest man – made structures in the world and stretch for thousands of kilometers each. These fences started with ecological chain reactions called trophic cascades affects an entire continent’s ecology.
The absence of dingoes, a top predator, on one side of the fence means that populations of prey species such as kangaroos can explode, which can cause categorical shifts in the composition of plants and even deplete the soil’s nutrients. On either side of the fence there are now two different “ecological universes. “
Our review has shown that fences affect ecosystems on every scale, leading to changes that in the worst cases can result in what some conservation biologists have already described.ecological collapse. “But this danger is often overlooked.
To demonstrate this point, we took a closer look at the Western USA, which is known for large open spaces, but also the homeland of barbed wire fences. Our analysis shows that large areas are considered by researchers to be relatively untrapped by the human footprint is quietly entangled in dense networks of fences.
Do less damage
Fences are clearly here to stay. As fencing ecology develops into a discipline, practitioners need to consider the complex roles that fencing plays in the social, economic, and political systems of man. However, there is still enough evidence to identify actions that can reduce its harmful effects.
There are many ways to change the design and construction of the fence without affecting their functions. For example, in Wyoming and Montana, federal land managers have experimented with game-friendly designs that allow species of antelope to move through fences with fewer obstacles and injuries. This type of adaptation shows great promise for wildlife and can have wider ecological benefits.
Another option is to align fences along natural ecological boundaries, such as watercourses or topographical features. This approach can help limit its impact on ecosystems at low cost. And land agencies or non-profit organizations can provide incentives for landowners to remove fences that are abandoned and no longer serve a purpose.
Nevertheless, once a fence is built, its consequences are long lasting. Even after removal, “ghost fencescan survive, and species continue acts as if a fence had been present for generations.
Because we know this, we believe that policymakers and landowners should be more careful about installing fences in the first place. Instead of considering only a fence’s short-term goal and the landscape nearby, we would like to see people see a new fence as another permanent link in a chain that often surrounds the planet.
Alex McInturff, Postdoctoral Researcher, University of California Santa Barbara; Christine Wilkinson, Ph.D. Candidate in Environmental Science, Policy and Management, University of California, Berkeley, en Wenjing Xu, PhD candidate in Environmental Science, Policy and Management, University of California, Berkeley