Sarah Dunn, GSA 2022 Science Communication Intern
Dr. Emily Fairfax, an associate professor at California State University Channel Islands, spends a lot of time looking for beaver dams. Walking along a creek, you might recognize a beaver dam as a wall of sticks with ends gnawed to spears, held together with mud and stones. These constructions slow water and create deep pools that provide beavers with protection from predators. Beavers are persistent dam builders, yet these dams can be challenging to systematically locate if you aren’t able to walk up every creek.
Researchers have typically used photos taken from planes or space to find beaver dams and ponds. A researcher might search through thousands of images on their computer. Fairfax explains that this approach “takes a lot of time and a lot of effort, and it makes your eyes tired.” She also notes that dams can look drastically different from place to place. “Beavers are not just a physics-based process… this is a structure built by a rodent with an agenda we don’t understand entirely.” Depending on the site and the individual beaver, their dams might be sinuous and long, impounding a series of blue splats surrounded by bright green, or their dams might be short and straight, crossing small streams and hardly creating a pool.
Beavers are recognized as ecosystem engineers for the role they have in shaping river corridors. Their ponds store water, their dams split rivers into multiple channels, and the increased subsurface water storage allows lush green vegetation to thrive in otherwise dry landscapes. The rodents have become icons in a movement spanning river science and restoration, in which “beaver believers” tout their ability to transform landscapes with little help from humans.
Since the European fur trade decimated the North American beaver population, the large rodents are slowly reinhabiting their historic range. Research into the impacts of beaver recolonization shows promising results. Beaver dams can reduce stream incision, provide fish habitat, promote nutrient cycling, and increase water storage during drought. Indeed, Fairfax’s early research found that “just having beavers being beavers can make landscapes more resistant to those types of disasters” (drought and wildfire).
Despite beavers’ growing recognition and popularity, most beaver research has remained limited in scope due to the difficulty of locating, accessing, and tracking beaver ponds through time. Scientists often study one pond in detail, or perhaps a collection of ponds within a single watershed. The inefficiency of finding beaver dams hampers scientists’ ability to understand beavers on the landscape scale. “We don’t have time to just spend mapping out all the beaver dams,” Fairfax explains. “Climate change is not waiting; we need to do bigger studies to help inform management decisions. This is perfect for remote sensing.”
Fairfax decided to enlist computers’ help to find all the beaver dams. Her research team built a convolutional neural network, cleverly called the Earth Engine Automated Geospatial Element Recognition (EEAGER) Model. The model uses high-resolution images and topographic data to find beaver dams. “It can be really creepy,” jokes Dr. Fairfax, noting that “this is the same model type as facial recognition… it learns patterns, shapes, and textures, not just pictures.” Her team gave the model thousands of known beaver dam locations, as well as tens of thousands of locations where there were no beaver dams. The model then searched for beavers.
So far, EEAGER’s results are promising. The model can find dams in areas both near and far from the training data, as well as in urban environments. It can also process historical images, allowing scientists to track how beaver populations are changing over time, especially as climate change expands their range. Additionally, finding dam locations will help managers more effectively evaluate beaver conservation efforts.
Fairfax encourages everyone to put the beavers on iNaturalist, a community-science application. By recording where you see beavers and their dams, you can help scientists verify the model results.