Credit: Troy Harrison / Moment / Getty Images Plus.
North American beavers are rebounding after centuries of hunting, habitat loss and disease, benefitting the broader natural ecosystem and humans alike.
Before European colonisation of North America, there were huge numbers of beavers on the continent. Estimates range from 60 to 140 million individuals. Today the population in North America is just 10–15 million.
New research published in the journal Communications Earth & Environment shows how reintroduced beavers have made the most positive impact.
The researchers say the results could inform decisions about land, wildlife and waterway management programs.
“Our findings can help land managers figure out where beaver activity will have the biggest impact,” says lead author Luwen Wan, from Stanford University, USA. “It gives them a practical tool for using nature to solve water and climate problems.”
Although cute, beavers aren’t universally loved. Their dams flood farmers’ fields and can block drainage from a busy highway.
But their dynamic and rapid dam construction is a huge boon for natural watershed management. Beaver dams create cool ponds which become homes for a diversity of other creatures. They also improve water quality and limit the spread of wildfires.
“Beaver wetland complexes” are networks of surface water and vegetation formed when beavers construct multiple dams in an area. These complexes recharge groundwater and are long-term freshwater stores. This is important in areas suffering from low surface and groundwater due to high use and drying from climate change.
“Beavers are naturally doing a lot of the things that we try to do as humans to manage river corridors,” says senior author Kate Maher, also at Stanford. “Humans will build one structure, leave it there, and hope it lasts for many decades. Beavers on the other hand, build little, tiny dams where they’re needed and flexibly manage what’s going on with the water in their environment.”
Maher and Wan joined with University of Minnesota beaver expert Emily Fairfax to try and map the impact of beaver dams where the industrious mammals have been reintroduced.
Traditional ground-based surveys don’t cover a big enough area while beaver dams and ponds are too small to be picked up by satellite imagery.
So the team used high-resolution aerial imagery from the US Department of Agriculture (USDA) National Agricultural Imagery Program to map more than 80 beaver pond complexes in varying landscapes across the US states of Colorado, Wyoming, Montana and Oregon.
They identified – with help from machine learning algorithms – key factors for the impact of the beavers which they linked to the topography, vegetation, local climate, soil and water flow.
For example, they found that longer dams led to larger ponds. These could increase ecosystem benefits like cooler air temperatures and more habitat for fishes.
Unmanaged beaver populations, however, can pose a flooding threat to homes, crops and infrastructure.
“There’s definitely a lot of exuberance around reintroducing beavers, and it may not be that every beaver reintroduction project is the right one to pursue,” Maher explains. “It’s important to understand those trade-offs and the risks and rewards from either intentionally reintroducing beavers, or just their natural return to watersheds.”
The team say their research will help in assessing where to introduce beavers as the population bounces back.