EnglishBy Jason G. Goldman
This is the second article in a three-part series on connectivity. Click here to read part one: “Coexistence, Not Corrals” and click here to read part three: “Making Way for Monkeys.”
The natural world is being carved and sliced into smaller and smaller parcels. Forests and grasslands and deserts are becoming like individually wrapped fun-size candy bars of nature, each with its own fragmented community of wild plants and animals. The natural world is in many ways a collection of islands; where they’re not separated by water, they’re separated by pavement.
In 2015, a global team of researchers estimated that seventy percent of the planet’s forests lie within just one kilometer of an edge. One out of every five trees is rooted within just one hundred meters of an edge. That’s less than the length of an American football field. Fragmented habitats have lower species richness, lower nutrient retention, and lower animal movement.
Given how rapidly the Earth’s landscape has become fragmented in recent decades, the long-term impacts on biodiversity remain unknown. Depending on the animals or plants in question, it might take years or even decades before the effects of fragmentation begin to become apparent. Still, reversing those effects has, in many places, already begun.
Habitat restoration is one strategy to reverse the effects of fragmentation, but there are many places where this is simply impossible. In those places, researchers and conservationists have turned to mitigation strategies instead: if the habitat fragments can’t be fully reintegrated, perhaps we can provide opportunities for animals to safely move between them. It wouldn’t just help to maintain genetic diversity, but to perpetuate the movement of nutrients across a wider landscape.
Here are some of the ways that conservationists are experimenting with increasing connectedness, in Central America and around the world.
Living Fences
Starting nearly a decade ago, Paso Pacifico began working with landowners in Nicaragua’s Paso del Istmo region to reforest small areas of their farms and ranches. By prioritizing areas near rivers or existing forests, the idea was to increase the amount of space available to wildlife. In all, some 250 hectares were restored in this way. The problem for landowners was that any reforestation meant losing out on potential financial gains from working that land.
To circumvent that problem, Paso Pacifico began encouraging the cultivation of living fencerows, a mix of native tree species that could be planted alongside existing property lines or field boundaries. It’s a strategy that was already becoming widespread throughout Central America.
Fencerows can have a tremendous impact on biodiversity. One study conducted in Costa Rica and Nicaragua documented at least 167 animal species within fence rows, including birds, bats, beetles, and butterflies. Animals used fencerows to feed on fruits, flowers, and nectar. They used them for shelter. Some were even seen mating within them. Perhaps most importantly, birds, bats, and monkeys have all been documented using fencerows as travel corridors. Even so, at one site, at least a third of the birds observed in fencerows were considered “forest dependent.” It means that these corridors weren’t just used for travel but functioned themselves as suitable habitat.
It’s not just beneficial for wildlife. Farmers can use their living fencerows as well, sustainably harvesting fruit and firewood for sale or for their own personal use. As with most conservation strategies, the most productive ones benefit people and animals alike.
The Right (of) Way
Long rows of trees and shrubs can create travel corridors for wildlife even in the most heavily developed parts of Europe and North America. Some utility companies there have begun to treat their easements and rights-of-way, such as the space below aerial power-lines, alongside railroads and highways, or above gas pipes as potential wildlife habitats.
Like the fencerows of Central America, these corridors aren’t only a means of traveling between two larger, protected areas, but function as habitats themselves. According to a 2016 study conducted in Sweden, for example, power-line corridors were important habitats for butterflies, whether or not they were near larger forests. It turned out that power-line corridors increased butterfly diversity in an area ten times wider than the corridor itself.
Similarly, of all native ant, spider, and grasshopper species in the Netherlands, more than half have been recorded using these bits of habitat, including a number of threatened or endangered species. In North Carolina, rare toads, turtles, and snakes have been spotted in roadside patches, and in Australia you can find two rare types of pygmy possums alongside highways – if you look closely enough.
Rights-of-way are also helpful for conserving rare plants. In Australia, green corridors along highways are home to most of the remaining individuals for two rare types of Acacia; more than a fifth of 32 rare plant species in Sweden rely on rights-of-way for their continued survival.
To be sure, rights-of-way can only offer suitable habitats insofar as they are managed with biodiversity in mind. That’s why the Kansas Audubon Society consults with the state’s Department of Transportation, for example, to develop sustainable mowing practices and seeding disturbed sites with native vegetation. It’s why in Tennessee, the Department of Transportation now waits to mow until winter begins, allowing the vegetation growing alongside its 13,000 miles of roads to provide useful habitat all spring and summer. It’s also why an Indiana-based power company has begun cultivating wildflowers beneath some eighty acres of solar panels in an effort to aid pollinator conservation in tandem with a shift to more sustainable energy generation.
Bridges and Tunnels
The last remaining migration of pronghorn antelopes occurs in western Wyoming. The 150-mile “Path of the Pronghorn” is one of the longest mammal migrations left in North America, but the corridor intersects with roads and highways. Twice each year, up to two thousand pronghorn – and another three thousand mule deer – pass through the area. They’ve been using this stretch of what is now highway 191 for at least six thousand years.
Several years ago, the state of Wyoming decided to install eight crossings along twelve miles of US Highway 191: two overpasses and six underpasses, each with strategically placed fencing to funnel animals towards those spots. Before the crossings were built, there were 85 wildlife-vehicle collisions per year, on average. Afterwards, that number dropped by 70 percent. By the fourth year, every single pronghorn successfully avoided crossing the highway’s asphalt-covered surface
Elsewhere, Canada’s Banff National Park, through which passes the Trans-Canada Highway, has six wildlife bridges – and a whopping thirty-eight tunnels. That’s the highest number of crossings in a single area anywhere on the planet. According to one study, over the course of sixteen years, eleven species of large mammals, prey and predators alike, were recorded using them more than 150,000 times. The elk were so eager to use them that they didn’t even need to wait for construction to be completed!
Bridges can even be in the sky. In South India, lion tailed macaques – an endangered monkey found only in this part of the world – were too often killed trying to cross a highway that cut through their forest. To solve the problem, a group of NGOs worked together with the government to fund the installation of aerial bridges, connecting the tree canopy on either side of the road. It’s a fairly low-cost way to ensure that monkeys, and other animals that spend their time among the leaves and branches, can avoid the threat of becoming roadkill.