To hear the poet Robert Frost tell it, when two roads diverge in a wood they create a lifechanging opportunity. While this may be true for humans, for the plants and animals in the wood those roads can be deadly.
Roads, bridges and trails help people get where we want to go, but for many species of wildlife they do just the opposite. Even something as seemingly minor as a fence can disrupt a fragile wildlife corridor, a small nature highway that allows animals like birds, deer and insects to move from one piece of habitat to another. This movement is critical to many species’ survival, especially in the face of climate change.
Build wildlife habitat connectivity in your neighborhood or backyard
Plant native plants, and keep them healthy.
“Native bugs like native plants and native birds like native bugs,” says Lori Hennings, a Metro natural resource scientist. She recommends ocean spray as one of many insect-friendly native shrubs to plant at home.
Prevent bird strikes.
Window decals or external screens can help birds avoid collisions with windows, which can be deadly.
Be mindful of your pets.
Cats and dogs can make wildlife nervous and close off habitat connections. Consider keeping your cats inside – our furry feline friends can have a bigger impact on local wildlife than wild predators do.
This is especially helpful for pollinators like bees and butterflies, who are very sensitive to pesticides.
These wildlife corridors are at the heart of a years-long effort led by Lori Hennings, a natural resource scientist at Metro and cofounder of the Regional Habitat Connectivity Work Group with Ted Labbe of the Urban Greenspaces Institute. Comprised of more than 45 partner organizations, the group is focused on mapping habitat connectivity in the greater Portland area to preserve the connections that still exist, and create new ones whenever possible.
“Without connectivity, our wildlife species aren’t going to be able to adapt to climate change,” Hennings says. “We’re going to lose species over time.”
Animals and plants need ample food, water and habitat to survive, but they also need a diverse enough gene pool to reproduce. When a natural area is surrounded by roads, fences and people, the plants and animals that live there become stranded, with no way to get in or out. Eventually, many of those species will die out, especially if temperatures rise and they aren’t able to move to new habitat.
As Hennings explains it, sometimes a barrier can be as simple as a gap in vegetation or a recreational trail. When a barrier is present, none of the habitat on the other side of that barrier is available to the species that need it. Habitat becomes fragmented, then isolated over time. Studies show that isolated habitat patches lose wildlife species, and without connectivity there is no way for them to repopulate.
With careful planning though, small corridors of natural areas between larger habitats can be left undisturbed, or developed areas can be restored to create corridors. These connections greatly improve outcomes for plants and wildlife. In other words, connected habitats are greater than the sum of their parts.
That’s why Hennings and her colleagues in the work group have developed a series of user-friendly models to help developers, planners and other land-use decision makers learn how to preserve wildlife corridors and maintain the habitat connections that still exist. The models help identify the region’s remaining habitat and connecting corridors, and they’re designed to be specific enough to identify conditions at a small, site-level scale.
The project has taken years, first spent developing methods to study habitat connectivity, then using computer mapping to identify and map potential wildlife corridors in the greater Portland area. After the computer modeling phase, researchers venture out to verify the corridors found on the maps. There could be new homes and roads built, for instance, or an insurmountable barrier that certain wildlife species simply cannot cross.
The connectivity models use what are called surrogate species to identify wildlife corridors in a given area. These species represent three different types of habitat: forested, wetlands and oak woodland. By using information about how the surrogate species move within and between these habitats, the models can predict how similar species would fare in similar types of habitat.
For instance, the alligator lizard represents other small animals that like to take cover under the thickets and downed logs found in oak woodlands. And the Douglas squirrel, which moves by jumping from branch to branch, represents animals that need forested areas where trees grow close together.
“Let’s say you have a thrush that has specific habitat needs, and you identify two habitats for the bird,” says Hennings. “You can use the models to see where opportunities exist to improve connections.”
To see this concept in action, look no further than the large patches of upland forest from Gresham to Happy Valley known as the East Buttes. Metro and the City of Gresham own a significant collection of properties in the area, which spans two counties and bridges the Johnson Creek and Clackamas River watersheds. When making decisions about where to purchase land or restore habitat, the potential for habitat connectivity is a top priority.
“Wildlife and plants have to have a way to move around neighborhoods,” says natural resource scientist Kate Holleran, who oversees Metro’s work in the East Buttes. “If we want our common wildlife to stay common, and we want to keep those species here, they have to have a way to move.”
The East Buttes area is mostly conifer hardwood forest, growing up around a series of extinct cinder cones in the Boring Lava Field. Applying the habitat connectivity models, then, it’s a forested area with four surrogate species: rubber boa, Swainson’s thrush, Douglas squirrel and North American beaver.
Take the mighty beaver. North American beavers thrive in streamside habitats found in the East Buttes, but they’re shy animals who are often hit by cars in developed areas. Thanks to information from the models and fieldwork done by researcher Amanda Temple, Holleran knows roads are a major barrier to connecting beaver habitat.
Something as simple as widening a culvert to allow beavers to pass under a road, instead of over it where they might be killed by a car, can improve the lives of generations of affable, tree-chomping rodents to come.
Keeping these habitats connected is a daunting task, especially with a changing climate and a growing human population in the area. But Holleran is optimistic, and says wildlife corridors are coming up more and more in the conversations she’s having with partner organizations in the East Buttes.
“We’re keenly aware of the desire to protect some functional connectivity,” she says, “and we have the potential to do it.”
Later this year, the models from the Regional Connectivity Habitat Work Group will be available to the public. Anyone who’s interested can access interactive maps, or download data to show where the wildlife corridors are in a specific area. Hennings hopes the models will be used in planning everything from bridges to bus routes. Even in heavily developed areas, small changes can be made to increase connections, like removing barbed wire from a fence or leaving a row of trees intact to preserve the canopy.
“Narrow is better than nothing,” she says. And every bit of connectivity helps.