Happy Trails Unholy Seeding and Bio-Superhighways

Humans have been creating trails since before recorded time.

Since before we were a species, even. Modern adventurers see them as paths for mountain biking, hiking, trail running, climbing, or canoe tripping, but old or new, our endeavors usually follow lines on the map previously tracked by our species. Yet in some places, these dirt conduits are still used for their age-old purposes of reaching water, finding food, or making seasonal migrations.

If this sounds like what animals do, you’re right. Nor are they choosy. They readily use trails made by other animals and humans as easily as their own. This reciprocation sets up an interesting dynamic for all involved, one that’s seldom discussed but should be part of the conversation in the planning of any trail or trail network.

Movements are the primary behavioral adaptation of animals (and, once upon a time, all humans) to variability in time and space of resources. Categorized into functional groups such as foraging, dispersal and migration, among others, they are studied by biologists and ecologists using a range of methodologies. Through modern technologies like radio telemetry, satellite tracking, remote- triggered digital cameras and drones, we’ve learned much about animal movements.

The biggest takeaway is that trails of any kind are superhighways for a range of terrestrial—and even aerial—species, from insects to megafauna. And though we might expect frequent human use of forest trails to make other animals less likely to do so, research shows zero-to-low negative impact on most mammals (though ungulates like deer are a different story, as they can associate certain trails with hunting danger).

If the level of human activity is high enough to cause disturbance, however, it can lead to changes in animal behavior and distribution patterns. Most of us are familiar with the trails of larger animals (ourselves included), yet they also create space for flying insects, birds and bats to navigate the understory. Because trails allow sunlight to penetrate where it often otherwise wouldn’t, these become dispersal corridors for plants, which coopt animal travelers to move their seeds—whether as burrs sticking to fur, or berries consumed at one sunny spot and defecated at another. Herbivores are particularly attracted to these concentrations of plants, which, in turn, attract carnivore predators to hang around as well.

This is something traditionally trained trailbuilders keep in mind, but that many enthusiastic amateur builders don’t often consider—or are even aware of. And as the impact on ecosystems and wildlife increases, it’s something that needs to change. We need to remember how much biological industry and behavior our trails are subsidizing when we “suddenly” find them interfering with our own use—like coming across a bear munching on berries that wouldn’t otherwise grow there, or a rattlesnake using a nice, warm path to stretch out in the sun.

These trails’ role in spreading plants and seeds, however, has also led to a rapidly growing problem: They spread destructive invasive plants as easily as native ones, both via wild animals and humans. We might not have fur, but we easily carry plant seeds or fragments on our clothing, shoes and even tires (next time you start a hike or bike at a popular trailhead, take note of how far dandelions and other invasive plants follow you down the trail).

It isn’t only riding that leads to this unholy seeding, but trail-building itself—especially unsanctioned construction by nonprofessionals—given how easy it is to spread noxious invasives like thistle, knapweed, Scotch broom and orange hawkweed on clothing, as well as via transported soil or uncleaned tools. Let’s put it this way: Trail-building without keeping these biological impacts in mind can be like sending an IV drip of ecosystem-destroying plants deep into pristine backcountry.

Worst-case scenarios involve shade-tolerant invasives like English ivy, a plant brought to the Pacific Northwest by European immigrants in the 19th century. It remained docile until it erupted in the 1980s—and here you can finger a criticalmass like climate change—turning healthy, living forests into “ivy deserts.” Since 2005, the City of Seattle has spent more than $11 million and 400,000 hours of volunteer labor removing invasive plants, mainly ivy, from its parks, at a cost of $25,000 to restore each acre.

But, just as our ancestors did, humans and wildlife can coexist. We just need to be conscious and intentional. When building in or near sensitive ecosystems like south-facing slopes and meadows, open-canopy forest, and wetland, river and lake margins, biologists can help route trails so as not to come close to areas where small animals like ground-nesting birds or reptiles nest or den, or not to cut off these habitats from other areas utilized by these creatures.

A good example in the Pacific Northwest is the rare and highly endangered sharp-tailed snake, a burrowing, pencil-thin slug eater that is only a foot long in adulthood with a home range of about a 160-foot radius. When building trail near sharp-tailed snake habitat, it isn’t hard to simply go around. It just requires paying attention.

We tend to see trails we modify or create as our own, but they don’t remain exclusive. Whether they were in use before we found them or have become new routes for wildlife, it behooves us to treat trails as shared natural spaces with potential real impacts, and respect that while for us they may be a means to adventure, other organisms still count on them for their livelihood.

Stop the Spread:

  • Remove plants, animals and mud from your shoes, bike, tires, gear and pets.
  • Clean your gear—including trail-building tools— before entering and leaving the trail.
  • Stay on designated roads and trails, both for riding and for building.
  • Only use dirt from a trail’s immediate area, and only use local or certified wood.